xref: /btstack/src/classic/rfcomm.c (revision 98451c7b102094e15e0a72ca2f7098d91aed2017)
1 /*
2  * Copyright (C) 2014 BlueKitchen GmbH
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  *
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  * 3. Neither the name of the copyright holders nor the names of
14  *    contributors may be used to endorse or promote products derived
15  *    from this software without specific prior written permission.
16  * 4. Any redistribution, use, or modification is done solely for
17  *    personal benefit and not for any commercial purpose or for
18  *    monetary gain.
19  *
20  * THIS SOFTWARE IS PROVIDED BY BLUEKITCHEN GMBH AND CONTRIBUTORS
21  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
22  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
23  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MATTHIAS
24  * RINGWALD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
25  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
26  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
27  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
28  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
29  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
30  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31  * SUCH DAMAGE.
32  *
33  * Please inquire about commercial licensing options at
34  * [email protected]
35  *
36  */
37 
38 #define BTSTACK_FILE__ "rfcomm.c"
39 
40 /*
41  *  rfcomm.c
42  */
43 
44 #include <string.h> // memcpy
45 #include <stdint.h>
46 
47 #include "bluetooth_sdp.h"
48 #include "btstack_debug.h"
49 #include "btstack_event.h"
50 #include "btstack_memory.h"
51 #include "btstack_util.h"
52 #include "classic/core.h"
53 #include "classic/rfcomm.h"
54 #include "hci.h"
55 #include "hci_cmd.h"
56 #include "hci_dump.h"
57 #include "l2cap.h"
58 
59 // workaround for missing PRIxPTR on mspgcc (16/20-bit MCU)
60 #ifndef PRIxPTR
61 #if defined(__MSP430X__)  &&  defined(__MSP430X_LARGE__)
62 #define PRIxPTR "lx"
63 #else
64 #define PRIxPTR "x"
65 #endif
66 #endif
67 
68 // ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE_FOR_RFCOMM requires ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE
69 #ifdef ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE_FOR_RFCOMM
70 #ifdef ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE
71 #define RFCOMM_USE_OUTGOING_BUFFER
72 #define RFCOMM_USE_ERTM
73 #else
74 #error "ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE_FOR_RFCOMM requires ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE. "
75 #error "Please disable ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE_FOR_RFCOMM, or, "
76 #error "enable ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE"
77 #endif
78 #endif
79 
80 #define RFCOMM_MULIPLEXER_TIMEOUT_MS 60000
81 
82 #define RFCOMM_CREDITS 10
83 
84 // FCS calc
85 #define BT_RFCOMM_CODE_WORD         0xE0 // pol = x8+x2+x1+1
86 #define BT_RFCOMM_CRC_CHECK_LEN     3
87 #define BT_RFCOMM_UIHCRC_CHECK_LEN  2
88 
89 // Control field values      bit no.       1 2 3 4 PF 6 7 8
90 #define BT_RFCOMM_SABM       0x3F       // 1 1 1 1  1 1 0 0
91 #define BT_RFCOMM_UA         0x73       // 1 1 0 0  1 1 1 0
92 #define BT_RFCOMM_DM         0x0F       // 1 1 1 1  0 0 0 0
93 #define BT_RFCOMM_DM_PF      0x1F       // 1 1 1 1  1 0 0 0
94 #define BT_RFCOMM_DISC       0x53       // 1 1 0 0  1 0 1 0
95 #define BT_RFCOMM_UIH        0xEF       // 1 1 1 1  0 1 1 1
96 #define BT_RFCOMM_UIH_PF     0xFF       // 1 1 1 1  0 1 1 1
97 
98 // Multiplexer message types
99 #define BT_RFCOMM_CLD_CMD    0xC3
100 #define BT_RFCOMM_FCON_CMD   0xA3
101 #define BT_RFCOMM_FCON_RSP   0xA1
102 #define BT_RFCOMM_FCOFF_CMD  0x63
103 #define BT_RFCOMM_FCOFF_RSP  0x61
104 #define BT_RFCOMM_MSC_CMD    0xE3
105 #define BT_RFCOMM_MSC_RSP    0xE1
106 #define BT_RFCOMM_NSC_RSP    0x11
107 #define BT_RFCOMM_PN_CMD     0x83
108 #define BT_RFCOMM_PN_RSP     0x81
109 #define BT_RFCOMM_RLS_CMD    0x53
110 #define BT_RFCOMM_RLS_RSP    0x51
111 #define BT_RFCOMM_RPN_CMD    0x93
112 #define BT_RFCOMM_RPN_RSP    0x91
113 #define BT_RFCOMM_TEST_CMD   0x23
114 #define BT_RFCOMM_TEST_RSP   0x21
115 
116 typedef enum {
117     CH_EVT_RCVD_SABM = 1,
118     CH_EVT_RCVD_UA,
119     CH_EVT_RCVD_PN,
120     CH_EVT_RCVD_PN_RSP,
121     CH_EVT_RCVD_DISC,
122     CH_EVT_RCVD_DM,
123     CH_EVT_RCVD_MSC_CMD,
124     CH_EVT_RCVD_MSC_RSP,
125     CH_EVT_RCVD_NSC_RSP,
126     CH_EVT_RCVD_RLS_CMD,
127     CH_EVT_RCVD_RLS_RSP,
128     CH_EVT_RCVD_RPN_CMD,
129     CH_EVT_RCVD_RPN_REQ,
130     CH_EVT_RCVD_CREDITS,
131     CH_EVT_MULTIPLEXER_READY,
132     CH_EVT_READY_TO_SEND,
133 } RFCOMM_CHANNEL_EVENT;
134 
135 typedef struct rfcomm_channel_event {
136     RFCOMM_CHANNEL_EVENT type;
137     uint16_t dummy; // force rfcomm_channel_event to be 2-byte aligned -> avoid -Wcast-align warning
138 } rfcomm_channel_event_t;
139 
140 typedef struct rfcomm_channel_event_pn {
141     rfcomm_channel_event_t super;
142     uint16_t max_frame_size;
143     uint8_t  priority;
144     uint8_t  credits_outgoing;
145 } rfcomm_channel_event_pn_t;
146 
147 typedef struct rfcomm_channel_event_rpn {
148     rfcomm_channel_event_t super;
149     rfcomm_rpn_data_t data;
150 } rfcomm_channel_event_rpn_t;
151 
152 typedef struct rfcomm_channel_event_rls {
153     rfcomm_channel_event_t super;
154     uint8_t line_status;
155 } rfcomm_channel_event_rls_t;
156 
157 typedef struct rfcomm_channel_event_msc {
158     rfcomm_channel_event_t super;
159     uint8_t modem_status;
160 } rfcomm_channel_event_msc_t;
161 
162 
163 // global rfcomm data
164 static uint16_t      rfcomm_client_cid_generator;  // used for client channel IDs
165 
166 // linked lists for all
167 static btstack_linked_list_t rfcomm_multiplexers;
168 static btstack_linked_list_t rfcomm_channels;
169 static btstack_linked_list_t rfcomm_services;
170 
171 static gap_security_level_t rfcomm_security_level;
172 
173 #ifdef RFCOMM_USE_ERTM
174 static uint16_t rfcomm_ertm_id;
175 void (*rfcomm_ertm_request_callback)(rfcomm_ertm_request_t * request);
176 void (*rfcomm_ertm_released_callback)(uint16_t ertm_id);
177 #endif
178 
179 #ifdef RFCOMM_USE_OUTGOING_BUFFER
180 static uint8_t outgoing_buffer[1030];
181 #endif
182 
183 static int  rfcomm_channel_can_send(rfcomm_channel_t * channel);
184 static int  rfcomm_channel_ready_for_open(rfcomm_channel_t *channel);
185 static int rfcomm_channel_ready_to_send(rfcomm_channel_t * channel);
186 static void rfcomm_channel_state_machine_with_channel(rfcomm_channel_t *channel, const rfcomm_channel_event_t *event, int * out_channel_valid);
187 static void rfcomm_channel_state_machine_with_dlci(rfcomm_multiplexer_t * multiplexer, uint8_t dlci, const rfcomm_channel_event_t *event);
188 static void rfcomm_emit_can_send_now(rfcomm_channel_t *channel);
189 static int rfcomm_multiplexer_ready_to_send(rfcomm_multiplexer_t * multiplexer);
190 static void rfcomm_multiplexer_state_machine(rfcomm_multiplexer_t * multiplexer, RFCOMM_MULTIPLEXER_EVENT event);
191 
192 // MARK: RFCOMM CLIENT EVENTS
193 
194 static rfcomm_channel_t * rfcomm_channel_for_rfcomm_cid(uint16_t rfcomm_cid){
195     btstack_linked_item_t *it;
196     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
197         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
198         if (channel->rfcomm_cid == rfcomm_cid) {
199             return channel;
200         };
201     }
202     return NULL;
203 }
204 
205 static uint16_t rfcomm_next_client_cid(void){
206     do {
207         if (rfcomm_client_cid_generator == 0xffff) {
208             // don't use 0 as channel id
209             rfcomm_client_cid_generator = 1;
210         } else {
211             rfcomm_client_cid_generator++;
212         }
213     } while (rfcomm_channel_for_rfcomm_cid(rfcomm_client_cid_generator) != NULL);
214     return rfcomm_client_cid_generator;
215 }
216 
217 #ifdef RFCOMM_USE_ERTM
218 static rfcomm_multiplexer_t * rfcomm_multiplexer_for_ertm_id(uint16_t ertm_id) {
219     btstack_linked_item_t *it;
220     for (it = (btstack_linked_item_t *) rfcomm_multiplexers; it ; it = it->next){
221         rfcomm_multiplexer_t * multiplexer = ((rfcomm_multiplexer_t *) it);
222         if (multiplexer->ertm_id == ertm_id) {
223             return multiplexer;
224         };
225     }
226     return NULL;
227 }
228 
229 static uint16_t rfcomm_next_ertm_id(void){
230     do {
231         if (rfcomm_ertm_id == 0xffff) {
232             // don't use 0 as channel id
233             rfcomm_ertm_id = 1;
234         } else {
235             rfcomm_ertm_id++;
236         }
237     } while (rfcomm_multiplexer_for_ertm_id(rfcomm_ertm_id) != NULL);
238     return rfcomm_ertm_id;
239 }
240 
241 #endif
242 
243 // data: event (8), len(8), address(48), channel (8), rfcomm_cid (16)
244 static void rfcomm_emit_connection_request(rfcomm_channel_t *channel) {
245     log_info("RFCOMM_EVENT_INCOMING_CONNECTION addr %s channel #%u cid 0x%02x",
246              bd_addr_to_str(channel->multiplexer->remote_addr), channel->dlci>>1, channel->rfcomm_cid);
247     uint8_t event[11];
248     event[0] = RFCOMM_EVENT_INCOMING_CONNECTION;
249     event[1] = sizeof(event) - 2;
250     reverse_bd_addr(channel->multiplexer->remote_addr, &event[2]);
251     event[8] = channel->dlci >> 1;
252     little_endian_store_16(event, 9, channel->rfcomm_cid);
253     hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
254 	(channel->packet_handler)(HCI_EVENT_PACKET, 0, event, sizeof(event));
255 }
256 
257 // API Change: BTstack-0.3.50x uses
258 // data: event(8), len(8), status (8), address (48), server channel(8), rfcomm_cid(16), max frame size(16)
259 // next Cydia release will use SVN version of this
260 // data: event(8), len(8), status (8), address (48), handle (16), server channel(8), rfcomm_cid(16), max frame size(16)
261 static void rfcomm_emit_channel_opened(rfcomm_channel_t *channel, uint8_t status) {
262     log_info("RFCOMM_EVENT_CHANNEL_OPENED status 0x%x addr %s handle 0x%x channel #%u cid 0x%02x mtu %u",
263              status, bd_addr_to_str(channel->multiplexer->remote_addr), channel->multiplexer->con_handle,
264              channel->dlci>>1, channel->rfcomm_cid, channel->max_frame_size);
265     uint8_t event[18];
266     uint8_t pos = 0;
267     event[pos++] = RFCOMM_EVENT_CHANNEL_OPENED;  // 0
268     event[pos++] = sizeof(event) - 2;                   // 1
269     event[pos++] = status;                              // 2
270     reverse_bd_addr(channel->multiplexer->remote_addr, &event[pos]); pos += 6; // 3
271     little_endian_store_16(event,  pos, channel->multiplexer->con_handle);   pos += 2; // 9
272 	event[pos++] = channel->dlci >> 1;                                      // 11
273 	little_endian_store_16(event, pos, channel->rfcomm_cid); pos += 2;                 // 12 - channel ID
274 	little_endian_store_16(event, pos, channel->max_frame_size); pos += 2;   // max frame size
275     event[pos++] = channel->service ? 1 : 0;    // linked to service -> incoming
276     hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
277 	(channel->packet_handler)(HCI_EVENT_PACKET, 0, event, pos);
278 
279     // if channel opened successfully, also send can send now if possible
280     if (status) return;
281     if (rfcomm_channel_can_send(channel)){
282         rfcomm_emit_can_send_now(channel);
283     }
284 }
285 
286 // data: event(8), len(8), rfcomm_cid(16)
287 static void rfcomm_emit_channel_closed(rfcomm_channel_t * channel) {
288     log_info("RFCOMM_EVENT_CHANNEL_CLOSED cid 0x%02x", channel->rfcomm_cid);
289     uint8_t event[4];
290     event[0] = RFCOMM_EVENT_CHANNEL_CLOSED;
291     event[1] = sizeof(event) - 2;
292     little_endian_store_16(event, 2, channel->rfcomm_cid);
293     hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
294 	(channel->packet_handler)(HCI_EVENT_PACKET, 0, event, sizeof(event));
295 }
296 
297 static void rfcomm_emit_remote_line_status(rfcomm_channel_t *channel, uint8_t line_status){
298     log_info("RFCOMM_EVENT_REMOTE_LINE_STATUS cid 0x%02x c, line status 0x%x", channel->rfcomm_cid, line_status);
299     uint8_t event[5];
300     event[0] = RFCOMM_EVENT_REMOTE_LINE_STATUS;
301     event[1] = sizeof(event) - 2;
302     little_endian_store_16(event, 2, channel->rfcomm_cid);
303     event[4] = line_status;
304     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
305     (channel->packet_handler)(HCI_EVENT_PACKET, 0, event, sizeof(event));
306 }
307 
308 static void rfcomm_emit_port_configuration(rfcomm_channel_t *channel){
309     // notify client about new settings
310     uint8_t event[2+sizeof(rfcomm_rpn_data_t)];
311     event[0] = RFCOMM_EVENT_PORT_CONFIGURATION;
312     event[1] = sizeof(rfcomm_rpn_data_t);
313     (void)memcpy(&event[2], (uint8_t *)&channel->rpn_data,
314                  sizeof(rfcomm_rpn_data_t));
315     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
316     (channel->packet_handler)(HCI_EVENT_PACKET, channel->rfcomm_cid, event, sizeof(event));
317 }
318 
319 static void rfcomm_emit_can_send_now(rfcomm_channel_t *channel) {
320     log_debug("RFCOMM_EVENT_CHANNEL_CAN_SEND_NOW local_cid 0x%x", channel->rfcomm_cid);
321     uint8_t event[4];
322     event[0] = RFCOMM_EVENT_CAN_SEND_NOW;
323     event[1] = sizeof(event) - 2;
324     little_endian_store_16(event, 2, channel->rfcomm_cid);
325     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
326     (channel->packet_handler)(HCI_EVENT_PACKET, channel->rfcomm_cid, event, sizeof(event));
327 }
328 
329 // MARK RFCOMM RPN DATA HELPER
330 static void rfcomm_rpn_data_set_defaults(rfcomm_rpn_data_t * rpn_data){
331         rpn_data->baud_rate = RPN_BAUD_9600;  /* 9600 bps */
332         rpn_data->flags = 0x03;               /* 8-n-1 */
333         rpn_data->flow_control = 0;           /* no flow control */
334         rpn_data->xon  = 0xd1;                /* XON */
335         rpn_data->xoff = 0xd3;                /* XOFF */
336         rpn_data->parameter_mask_0 = 0x7f;    /* parameter mask, all values set */
337         rpn_data->parameter_mask_1 = 0x3f;    /* parameter mask, all values set */
338 }
339 
340 static void rfcomm_rpn_data_update(rfcomm_rpn_data_t * dest, rfcomm_rpn_data_t * src){
341     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_BAUD){
342         dest->baud_rate = src->baud_rate;
343     }
344     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_DATA_BITS){
345         dest->flags = (dest->flags & 0xfc) | (src->flags & 0x03);
346     }
347     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_STOP_BITS){
348         dest->flags = (dest->flags & 0xfb) | (src->flags & 0x04);
349     }
350     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_PARITY){
351         dest->flags = (dest->flags & 0xf7) | (src->flags & 0x08);
352     }
353     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_PARITY_TYPE){
354         dest->flags = (dest->flags & 0xfc) | (src->flags & 0x30);
355     }
356     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_XON_CHAR){
357         dest->xon = src->xon;
358     }
359     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_XOFF_CHAR){
360         dest->xoff = src->xoff;
361     }
362     int i;
363     for (i=0; i < 6 ; i++){
364         uint8_t mask = 1 << i;
365         if (src->parameter_mask_1 & mask){
366             dest->flags = (dest->flags & ~mask) | (src->flags & mask);
367         }
368     }
369     // always copy parameter mask, too. informative for client, needed for response
370     dest->parameter_mask_0 = src->parameter_mask_0;
371     dest->parameter_mask_1 = src->parameter_mask_1;
372 }
373 // MARK: RFCOMM MULTIPLEXER HELPER
374 
375 static uint16_t rfcomm_max_frame_size_for_l2cap_mtu(uint16_t l2cap_mtu){
376     // Assume RFCOMM header without credits and 2 byte (14 bit) length field
377     uint16_t max_frame_size = l2cap_mtu - 5;
378     log_info("rfcomm_max_frame_size_for_l2cap_mtu:  %u -> %u", l2cap_mtu, max_frame_size);
379     return max_frame_size;
380 }
381 
382 static void rfcomm_multiplexer_initialize(rfcomm_multiplexer_t *multiplexer){
383     multiplexer->state = RFCOMM_MULTIPLEXER_CLOSED;
384     multiplexer->fcon = 1;
385     multiplexer->send_dm_for_dlci = 0;
386     multiplexer->max_frame_size = rfcomm_max_frame_size_for_l2cap_mtu(l2cap_max_mtu());
387     multiplexer->test_data_len = 0;
388     multiplexer->nsc_command = 0;
389 }
390 
391 static rfcomm_multiplexer_t * rfcomm_multiplexer_create_for_addr(bd_addr_t addr){
392 
393     // alloc structure
394     rfcomm_multiplexer_t * multiplexer = btstack_memory_rfcomm_multiplexer_get();
395     if (!multiplexer) return NULL;
396 
397     // fill in
398     rfcomm_multiplexer_initialize(multiplexer);
399     bd_addr_copy(multiplexer->remote_addr, addr);
400 
401     // add to services list
402     btstack_linked_list_add(&rfcomm_multiplexers, (btstack_linked_item_t *) multiplexer);
403 
404     return multiplexer;
405 }
406 
407 static rfcomm_multiplexer_t * rfcomm_multiplexer_for_addr(bd_addr_t addr){
408     btstack_linked_item_t *it;
409     for (it = (btstack_linked_item_t *) rfcomm_multiplexers; it ; it = it->next){
410         rfcomm_multiplexer_t * multiplexer = ((rfcomm_multiplexer_t *) it);
411         // ignore multiplexer in shutdown
412         if (multiplexer->state == RFCOMM_MULTIPLEXER_SHUTTING_DOWN) continue;
413         if (bd_addr_cmp(addr, multiplexer->remote_addr) == 0) {
414             return multiplexer;
415         };
416     }
417     return NULL;
418 }
419 
420 static rfcomm_multiplexer_t * rfcomm_multiplexer_for_l2cap_cid(uint16_t l2cap_cid) {
421     btstack_linked_item_t *it;
422     for (it = (btstack_linked_item_t *) rfcomm_multiplexers; it ; it = it->next){
423         rfcomm_multiplexer_t * multiplexer = ((rfcomm_multiplexer_t *) it);
424         if (multiplexer->l2cap_cid == l2cap_cid) {
425             return multiplexer;
426         };
427     }
428     return NULL;
429 }
430 
431 static int rfcomm_multiplexer_has_channels(rfcomm_multiplexer_t * multiplexer){
432     btstack_linked_item_t *it;
433     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
434         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
435         if (channel->multiplexer == multiplexer) {
436             return 1;
437         }
438     }
439     return 0;
440 }
441 
442 // MARK: RFCOMM CHANNEL HELPER
443 
444 static void rfcomm_dump_channels(void){
445 #ifdef ENABLE_LOG_INFO
446     btstack_linked_item_t * it;
447     int channels = 0;
448     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
449         rfcomm_channel_t * channel = (rfcomm_channel_t *) it;
450         log_info("Channel #%u: addr %p, state %u", channels, channel, channel->state);
451         channels++;
452     }
453 #endif
454 }
455 
456 static void rfcomm_channel_initialize(rfcomm_channel_t *channel, rfcomm_multiplexer_t *multiplexer,
457                                rfcomm_service_t *service, uint8_t server_channel){
458 
459     // set defaults for port configuration (even for services)
460     rfcomm_rpn_data_set_defaults(&channel->rpn_data);
461 
462     channel->state            = RFCOMM_CHANNEL_CLOSED;
463     channel->state_var        = RFCOMM_CHANNEL_STATE_VAR_NONE;
464 
465     channel->multiplexer      = multiplexer;
466     channel->rfcomm_cid       = rfcomm_next_client_cid();
467     channel->max_frame_size   = multiplexer->max_frame_size;
468 
469     channel->credits_incoming = 0;
470     channel->credits_outgoing = 0;
471 
472     // incoming flow control not active
473     channel->new_credits_incoming  = RFCOMM_CREDITS;
474     channel->incoming_flow_control = 0;
475 
476     channel->rls_line_status       = RFCOMM_RLS_STATUS_INVALID;
477 
478     channel->service = service;
479 	if (service) {
480 		// incoming connection
481     	channel->dlci = (server_channel << 1) |  multiplexer->outgoing;
482         if (channel->max_frame_size > service->max_frame_size) {
483             channel->max_frame_size = service->max_frame_size;
484         }
485         channel->incoming_flow_control = service->incoming_flow_control;
486         channel->new_credits_incoming  = service->incoming_initial_credits;
487         channel->packet_handler        = service->packet_handler;
488 	} else {
489 		// outgoing connection
490 		channel->dlci = (server_channel << 1) | (multiplexer->outgoing ^ 1);
491 	}
492 }
493 
494 // service == NULL -> outgoing channel
495 static rfcomm_channel_t * rfcomm_channel_create(rfcomm_multiplexer_t * multiplexer,
496                                                 rfcomm_service_t * service, uint8_t server_channel){
497 
498     log_info("rfcomm_channel_create for service %p, channel %u --- list of channels:", service, server_channel);
499     rfcomm_dump_channels();
500 
501     // alloc structure
502     rfcomm_channel_t * channel = btstack_memory_rfcomm_channel_get();
503     if (!channel) return NULL;
504 
505     // fill in
506     rfcomm_channel_initialize(channel, multiplexer, service, server_channel);
507 
508     // add to services list
509     btstack_linked_list_add(&rfcomm_channels, (btstack_linked_item_t *) channel);
510 
511     return channel;
512 }
513 
514 static void rfcomm_notify_channel_can_send(void){
515     btstack_linked_list_iterator_t it;
516     btstack_linked_list_iterator_init(&it, &rfcomm_channels);
517     while (btstack_linked_list_iterator_has_next(&it)){
518         rfcomm_channel_t * channel = (rfcomm_channel_t *) btstack_linked_list_iterator_next(&it);
519         if (!channel->waiting_for_can_send_now) continue; // didn't try to send yet
520         if (!rfcomm_channel_can_send(channel)) continue;  // or cannot yet either
521 
522         channel->waiting_for_can_send_now = 0;
523         rfcomm_emit_can_send_now(channel);
524     }
525 }
526 
527 static rfcomm_channel_t * rfcomm_channel_for_multiplexer_and_dlci(rfcomm_multiplexer_t * multiplexer, uint8_t dlci){
528     btstack_linked_item_t *it;
529     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
530         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
531         if ((channel->dlci == dlci) && (channel->multiplexer == multiplexer)) {
532             return channel;
533         };
534     }
535     return NULL;
536 }
537 
538 static rfcomm_service_t * rfcomm_service_for_channel(uint8_t server_channel){
539     btstack_linked_item_t *it;
540     for (it = (btstack_linked_item_t *) rfcomm_services; it ; it = it->next){
541         rfcomm_service_t * service = ((rfcomm_service_t *) it);
542         if ( service->server_channel == server_channel){
543             return service;
544         };
545     }
546     return NULL;
547 }
548 
549 // MARK: RFCOMM SEND
550 
551 /**
552  * @param credits - only used for RFCOMM flow control in UIH wiht P/F = 1
553  */
554 static int rfcomm_send_packet_for_multiplexer(rfcomm_multiplexer_t *multiplexer, uint8_t address, uint8_t control, uint8_t credits, uint8_t *data, uint16_t len){
555 
556     if (!l2cap_can_send_packet_now(multiplexer->l2cap_cid)) return BTSTACK_ACL_BUFFERS_FULL;
557 
558 #ifdef RFCOMM_USE_OUTGOING_BUFFER
559     uint8_t * rfcomm_out_buffer = outgoing_buffer;
560 #else
561     l2cap_reserve_packet_buffer();
562     uint8_t * rfcomm_out_buffer = l2cap_get_outgoing_buffer();
563 #endif
564 
565 	uint16_t pos = 0;
566 	uint8_t crc_fields = 3;
567 
568 	rfcomm_out_buffer[pos++] = address;
569 	rfcomm_out_buffer[pos++] = control;
570 
571 	// length field can be 1 or 2 octets
572 	if (len < 128){
573 		rfcomm_out_buffer[pos++] = (len << 1)| 1;     // bits 0-6
574 	} else {
575 		rfcomm_out_buffer[pos++] = (len & 0x7f) << 1; // bits 0-6
576 		rfcomm_out_buffer[pos++] = len >> 7;          // bits 7-14
577 		crc_fields++;
578 	}
579 
580 	// add credits for UIH frames when PF bit is set
581 	if (control == BT_RFCOMM_UIH_PF){
582 		rfcomm_out_buffer[pos++] = credits;
583 	}
584 
585 	// copy actual data
586 	if (len) {
587 		(void)memcpy(&rfcomm_out_buffer[pos], data, len);
588 		pos += len;
589 	}
590 
591 	// UIH frames only calc FCS over address + control (5.1.1)
592 	if ((control & 0xef) == BT_RFCOMM_UIH){
593 		crc_fields = 2;
594 	}
595 	rfcomm_out_buffer[pos++] =  btstack_crc8_calc(rfcomm_out_buffer, crc_fields); // calc fcs
596 
597 #ifdef RFCOMM_USE_OUTGOING_BUFFER
598     int err = l2cap_send(multiplexer->l2cap_cid, rfcomm_out_buffer, pos);
599 #else
600     int err = l2cap_send_prepared(multiplexer->l2cap_cid, pos);
601 #endif
602 
603     return err;
604 }
605 
606 // simplified version of rfcomm_send_packet_for_multiplexer for prepared rfcomm packet (UIH, 2 byte len, no credits)
607 static int rfcomm_send_uih_prepared(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint16_t len){
608 
609     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) | (dlci << 2);
610     uint8_t control = BT_RFCOMM_UIH;
611 
612 #ifdef RFCOMM_USE_OUTGOING_BUFFER
613     uint8_t * rfcomm_out_buffer = outgoing_buffer;
614 #else
615     uint8_t * rfcomm_out_buffer = l2cap_get_outgoing_buffer();
616 #endif
617 
618     uint16_t pos = 0;
619     rfcomm_out_buffer[pos++] = address;
620     rfcomm_out_buffer[pos++] = control;
621     rfcomm_out_buffer[pos++] = (len & 0x7f) << 1; // bits 0-6
622     rfcomm_out_buffer[pos++] = len >> 7;          // bits 7-14
623 
624     // actual data is already in place
625     pos += len;
626 
627     // UIH frames only calc FCS over address + control (5.1.1)
628     rfcomm_out_buffer[pos++] =  btstack_crc8_calc(rfcomm_out_buffer, 2); // calc fcs
629 
630 #ifdef RFCOMM_USE_OUTGOING_BUFFER
631     int err = l2cap_send(multiplexer->l2cap_cid, rfcomm_out_buffer, pos);
632 #else
633     int err = l2cap_send_prepared(multiplexer->l2cap_cid, pos);
634 #endif
635 
636     return err;
637 }
638 
639 // C/R Flag in Address
640 // - terms: initiator = station that creates multiplexer with SABM
641 // - terms: responder = station that responds to multiplexer setup with UA
642 // "For SABM, UA, DM and DISC frames C/R bit is set according to Table 1 in GSM 07.10, section 5.2.1.2"
643 //    - command initiator = 1 /response responder = 1
644 //    - command responder = 0 /response initiator = 0
645 // "For UIH frames, the C/R bit is always set according to section 5.4.3.1 in GSM 07.10.
646 //  This applies independently of what is contained wthin the UIH frames, either data or control messages."
647 //    - c/r = 1 for frames by initiating station, 0 = for frames by responding station
648 
649 // C/R Flag in Message
650 // "In the message level, the C/R bit in the command type field is set as stated in section 5.4.6.2 in GSM 07.10."
651 //   - If the C/R bit is set to 1 the message is a command
652 //   - if it is set to 0 the message is a response.
653 
654 // temp/old messge construction
655 
656 // new object oriented version
657 static int rfcomm_send_sabm(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
658 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) | (dlci << 2);   // command
659     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_SABM, 0, NULL, 0);
660 }
661 
662 static int rfcomm_send_disc(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
663 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) | (dlci << 2);  // command
664     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_DISC, 0, NULL, 0);
665 }
666 
667 static int rfcomm_send_ua(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
668 	uint8_t address = (1 << 0) | ((multiplexer->outgoing ^ 1) << 1) | (dlci << 2); // response
669     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UA, 0, NULL, 0);
670 }
671 
672 static int rfcomm_send_dm_pf(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
673 	uint8_t address = (1 << 0) | ((multiplexer->outgoing ^ 1) << 1) | (dlci << 2); // response
674     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_DM_PF, 0, NULL, 0);
675 }
676 
677 static int rfcomm_send_uih_fc_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t fcon) {
678     uint8_t address = (1 << 0) | (multiplexer->outgoing<< 1);
679     uint8_t payload[2];
680     uint8_t pos = 0;
681     payload[pos++] = fcon ? BT_RFCOMM_FCON_RSP : BT_RFCOMM_FCOFF_RSP;
682     payload[pos++] = (0 << 1) | 1;  // len
683     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
684 }
685 
686 // static int rfcomm_send_uih_test_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t * data, uint16_t len) {
687 //     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
688 //     uint8_t payload[2+len];
689 //     uint8_t pos = 0;
690 //     payload[pos++] = BT_RFCOMM_TEST_CMD;
691 //     payload[pos++] = (len + 1) << 1 | 1;  // len
692 //     memcpy(&payload[pos], data, len);
693 //     pos += len;
694 //     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
695 // }
696 
697 static int rfcomm_send_uih_test_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t * data, uint16_t len) {
698     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
699     uint8_t payload[2+RFCOMM_TEST_DATA_MAX_LEN];
700     uint8_t pos = 0;
701     payload[pos++] = BT_RFCOMM_TEST_RSP;
702     if (len > RFCOMM_TEST_DATA_MAX_LEN) {
703         len = RFCOMM_TEST_DATA_MAX_LEN;
704     }
705     payload[pos++] = (len << 1) | 1;  // len
706     (void)memcpy(&payload[pos], data, len);
707     pos += len;
708     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
709 }
710 
711 static int rfcomm_send_uih_msc_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t signals) {
712 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
713 	uint8_t payload[4];
714 	uint8_t pos = 0;
715 	payload[pos++] = BT_RFCOMM_MSC_CMD;
716 	payload[pos++] = (2 << 1) | 1;  // len
717 	payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
718 	payload[pos++] = signals;
719 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
720 }
721 
722 static int rfcomm_send_uih_msc_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t signals) {
723 	uint8_t address = (1 << 0) | (multiplexer->outgoing<< 1);
724 	uint8_t payload[4];
725 	uint8_t pos = 0;
726 	payload[pos++] = BT_RFCOMM_MSC_RSP;
727 	payload[pos++] = (2 << 1) | 1;  // len
728 	payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
729 	payload[pos++] = signals;
730 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
731 }
732 
733 static int rfcomm_send_uih_nsc_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t command) {
734     uint8_t address = (1 << 0) | (multiplexer->outgoing<< 1);
735     uint8_t payload[3];
736     uint8_t pos = 0;
737     payload[pos++] = BT_RFCOMM_NSC_RSP;
738     payload[pos++] = (1 << 1) | 1;  // len
739     payload[pos++] = command;
740     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
741 }
742 
743 static int rfcomm_send_uih_pn_command(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint16_t max_frame_size){
744 	uint8_t payload[10];
745 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
746 	uint8_t pos = 0;
747 	payload[pos++] = BT_RFCOMM_PN_CMD;
748 	payload[pos++] = (8 << 1) | 1;  // len
749 	payload[pos++] = dlci;
750 	payload[pos++] = 0xf0; // pre-defined for Bluetooth, see 5.5.3 of TS 07.10 Adaption for RFCOMM
751 	payload[pos++] = 0; // priority
752 	payload[pos++] = 0; // max 60 seconds ack
753 	payload[pos++] = max_frame_size & 0xff; // max framesize low
754 	payload[pos++] = max_frame_size >> 8;   // max framesize high
755 	payload[pos++] = 0x00; // number of retransmissions
756 	payload[pos++] = 0x00; // (unused error recovery window) initial number of credits
757 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
758 }
759 
760 // "The response may not change the DLCI, the priority, the convergence layer, or the timer value." rfcomm_tutorial.pdf
761 static int rfcomm_send_uih_pn_response(rfcomm_multiplexer_t *multiplexer, uint8_t dlci,
762                                        uint8_t priority, uint16_t max_frame_size){
763 	uint8_t payload[10];
764 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
765 	uint8_t pos = 0;
766 	payload[pos++] = BT_RFCOMM_PN_RSP;
767 	payload[pos++] = (8 << 1) | 1;  // len
768 	payload[pos++] = dlci;
769 	payload[pos++] = 0xe0; // pre defined for Bluetooth, see 5.5.3 of TS 07.10 Adaption for RFCOMM
770 	payload[pos++] = priority; // priority
771 	payload[pos++] = 0; // max 60 seconds ack
772 	payload[pos++] = max_frame_size & 0xff; // max framesize low
773 	payload[pos++] = max_frame_size >> 8;   // max framesize high
774 	payload[pos++] = 0x00; // number of retransmissions
775 	payload[pos++] = 0x00; // (unused error recovery window) initial number of credits
776 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
777 }
778 
779 static int rfcomm_send_uih_rls_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t line_status) {
780     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
781     uint8_t payload[4];
782     uint8_t pos = 0;
783     payload[pos++] = BT_RFCOMM_RLS_CMD;
784     payload[pos++] = (2 << 1) | 1;  // len
785     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
786     payload[pos++] = line_status;
787     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
788 }
789 
790 static int rfcomm_send_uih_rls_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t line_status) {
791     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
792     uint8_t payload[4];
793     uint8_t pos = 0;
794     payload[pos++] = BT_RFCOMM_RLS_RSP;
795     payload[pos++] = (2 << 1) | 1;  // len
796     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
797     payload[pos++] = line_status;
798     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
799 }
800 
801 static int rfcomm_send_uih_rpn_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, rfcomm_rpn_data_t *rpn_data) {
802     uint8_t payload[10];
803     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
804     uint8_t pos = 0;
805     payload[pos++] = BT_RFCOMM_RPN_CMD;
806     payload[pos++] = (8 << 1) | 1;  // len
807     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
808     payload[pos++] = rpn_data->baud_rate;
809     payload[pos++] = rpn_data->flags;
810     payload[pos++] = rpn_data->flow_control;
811     payload[pos++] = rpn_data->xon;
812     payload[pos++] = rpn_data->xoff;
813     payload[pos++] = rpn_data->parameter_mask_0;
814     payload[pos++] = rpn_data->parameter_mask_1;
815     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
816 }
817 
818 static int rfcomm_send_uih_rpn_req(rfcomm_multiplexer_t *multiplexer, uint8_t dlci) {
819     uint8_t payload[3];
820     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
821     uint8_t pos = 0;
822     payload[pos++] = BT_RFCOMM_RPN_CMD;
823     payload[pos++] = (1 << 1) | 1;  // len
824     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
825     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
826 }
827 
828 static int rfcomm_send_uih_rpn_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, rfcomm_rpn_data_t *rpn_data) {
829 	uint8_t payload[10];
830 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
831 	uint8_t pos = 0;
832 	payload[pos++] = BT_RFCOMM_RPN_RSP;
833 	payload[pos++] = (8 << 1) | 1;  // len
834 	payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
835 	payload[pos++] = rpn_data->baud_rate;
836 	payload[pos++] = rpn_data->flags;
837 	payload[pos++] = rpn_data->flow_control;
838 	payload[pos++] = rpn_data->xon;
839 	payload[pos++] = rpn_data->xoff;
840 	payload[pos++] = rpn_data->parameter_mask_0;
841 	payload[pos++] = rpn_data->parameter_mask_1;
842 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
843 }
844 
845 static void rfcomm_send_uih_credits(rfcomm_multiplexer_t *multiplexer, uint8_t dlci,  uint8_t credits){
846     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) |  (dlci << 2);
847     rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH_PF, credits, NULL, 0);
848 }
849 
850 // depending on channel state emit channel opened with status or channel closed
851 static void rfcomm_channel_emit_final_event(rfcomm_channel_t * channel, uint8_t status){
852     // emit appropriate events
853     switch(channel->state){
854         case RFCOMM_CHANNEL_OPEN:
855         case RFCOMM_CHANNEL_W4_UA_AFTER_DISC:
856             rfcomm_emit_channel_closed(channel);
857             break;
858         case RFCOMM_CHANNEL_SEND_UA_AFTER_DISC:
859             // remote didn't wait until we send the UA disc
860             // close event already emitted
861             break;
862         default:
863             rfcomm_emit_channel_opened(channel, status);
864             break;
865     }
866 }
867 
868 // MARK: RFCOMM MULTIPLEXER
869 static void rfcomm_multiplexer_stop_timer(rfcomm_multiplexer_t * multiplexer){
870     if (multiplexer->timer_active) {
871         btstack_run_loop_remove_timer(&multiplexer->timer);
872         multiplexer->timer_active = 0;
873     }
874 }
875 static void rfcomm_multiplexer_free(rfcomm_multiplexer_t * multiplexer){
876     btstack_linked_list_remove( &rfcomm_multiplexers, (btstack_linked_item_t *) multiplexer);
877     btstack_memory_rfcomm_multiplexer_free(multiplexer);
878 }
879 
880 static void rfcomm_multiplexer_finalize(rfcomm_multiplexer_t * multiplexer){
881     // remove (potential) timer
882     rfcomm_multiplexer_stop_timer(multiplexer);
883 
884     // close and remove all channels
885     btstack_linked_item_t *it = (btstack_linked_item_t *) &rfcomm_channels;
886     while (it->next){
887         rfcomm_channel_t * channel = (rfcomm_channel_t *) it->next;
888         if (channel->multiplexer == multiplexer) {
889             // emit open with status or closed
890             rfcomm_channel_emit_final_event(channel, RFCOMM_MULTIPLEXER_STOPPED);
891             // remove from list
892             it->next = it->next->next;
893             // free channel struct
894             btstack_memory_rfcomm_channel_free(channel);
895         } else {
896             it = it->next;
897         }
898     }
899 
900     // remove mutliplexer
901     rfcomm_multiplexer_free(multiplexer);
902 }
903 
904 static void rfcomm_multiplexer_timer_handler(btstack_timer_source_t *timer){
905     rfcomm_multiplexer_t * multiplexer = (rfcomm_multiplexer_t*) btstack_run_loop_get_timer_context(timer);
906     if (rfcomm_multiplexer_has_channels(multiplexer)) return;
907 
908     log_info("rfcomm_multiplexer_timer_handler timeout: shutting down multiplexer! (no channels)");
909     uint16_t l2cap_cid = multiplexer->l2cap_cid;
910     rfcomm_multiplexer_finalize(multiplexer);
911     l2cap_disconnect(l2cap_cid, 0x13);
912 }
913 
914 static void rfcomm_multiplexer_prepare_idle_timer(rfcomm_multiplexer_t * multiplexer){
915     if (multiplexer->timer_active) {
916         btstack_run_loop_remove_timer(&multiplexer->timer);
917         multiplexer->timer_active = 0;
918     }
919     if (rfcomm_multiplexer_has_channels(multiplexer)) return;
920 
921     // start idle timer for multiplexer timeout check as there are no rfcomm channels yet
922     btstack_run_loop_set_timer(&multiplexer->timer, RFCOMM_MULIPLEXER_TIMEOUT_MS);
923     btstack_run_loop_set_timer_handler(&multiplexer->timer, rfcomm_multiplexer_timer_handler);
924     btstack_run_loop_set_timer_context(&multiplexer->timer, multiplexer);
925     btstack_run_loop_add_timer(&multiplexer->timer);
926     multiplexer->timer_active = 1;
927 }
928 
929 static void rfcomm_multiplexer_opened(rfcomm_multiplexer_t *multiplexer){
930     log_info("Multiplexer up and running");
931     multiplexer->state = RFCOMM_MULTIPLEXER_OPEN;
932 
933     const rfcomm_channel_event_t event = { CH_EVT_MULTIPLEXER_READY, 0};
934 
935     // transition of channels that wait for multiplexer
936     btstack_linked_item_t *it;
937     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
938         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
939         if (channel->multiplexer != multiplexer) continue;
940         int rfcomm_channel_valid = 1;
941         rfcomm_channel_state_machine_with_channel(channel, &event, &rfcomm_channel_valid);
942         if (rfcomm_channel_valid && rfcomm_channel_ready_to_send(channel)){
943             l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
944         }
945     }
946     rfcomm_multiplexer_prepare_idle_timer(multiplexer);
947 
948     // request can send now for multiplexer if ready
949     if (rfcomm_multiplexer_ready_to_send(multiplexer)){
950         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
951     }
952 }
953 
954 static void rfcomm_handle_can_send_now(uint16_t l2cap_cid){
955 
956     log_debug("rfcomm_handle_can_send_now enter: %u", l2cap_cid);
957 
958     btstack_linked_list_iterator_t it;
959     int token_consumed = 0;
960 
961     // forward token to multiplexer
962     btstack_linked_list_iterator_init(&it, &rfcomm_multiplexers);
963     while (!token_consumed && btstack_linked_list_iterator_has_next(&it)){
964         rfcomm_multiplexer_t * multiplexer = (rfcomm_multiplexer_t *) btstack_linked_list_iterator_next(&it);
965         if (multiplexer->l2cap_cid != l2cap_cid) continue;
966         if (rfcomm_multiplexer_ready_to_send(multiplexer)){
967             log_debug("rfcomm_handle_can_send_now enter: multiplexer token");
968             token_consumed = 1;
969             rfcomm_multiplexer_state_machine(multiplexer, MULT_EV_READY_TO_SEND);
970         }
971     }
972 
973     // forward token to channel state machine
974     btstack_linked_list_iterator_init(&it, &rfcomm_channels);
975     while (!token_consumed && btstack_linked_list_iterator_has_next(&it)){
976         rfcomm_channel_t * channel = (rfcomm_channel_t *) btstack_linked_list_iterator_next(&it);
977         if (channel->multiplexer->l2cap_cid != l2cap_cid) continue;
978         // channel state machine
979         if (rfcomm_channel_ready_to_send(channel)){
980             log_debug("rfcomm_handle_can_send_now enter: channel token");
981             token_consumed = 1;
982             const rfcomm_channel_event_t event = { CH_EVT_READY_TO_SEND, 0 };
983             int rfcomm_channel_valid = 1;
984             rfcomm_channel_state_machine_with_channel(channel, &event, &rfcomm_channel_valid);
985         }
986     }
987 
988     // forward token to client
989     btstack_linked_list_iterator_init(&it, &rfcomm_channels);
990     while (!token_consumed && btstack_linked_list_iterator_has_next(&it)){
991         rfcomm_channel_t * channel = (rfcomm_channel_t *) btstack_linked_list_iterator_next(&it);
992         if (channel->multiplexer->l2cap_cid != l2cap_cid) continue;
993         // client waiting for can send now
994         if (!channel->waiting_for_can_send_now)    continue;
995         if ((channel->multiplexer->fcon & 1) == 0) continue;
996         if (!channel->credits_outgoing){
997             log_debug("rfcomm_handle_can_send_now waiting to send but no credits (ignore)");
998             continue;
999         }
1000 
1001         log_debug("rfcomm_handle_can_send_now enter: client token");
1002         token_consumed = 1;
1003         channel->waiting_for_can_send_now = 0;
1004         rfcomm_emit_can_send_now(channel);
1005     }
1006 
1007     // if token was consumed, request another one
1008     if (token_consumed) {
1009         l2cap_request_can_send_now_event(l2cap_cid);
1010     }
1011 
1012     log_debug("rfcomm_handle_can_send_now exit");
1013 }
1014 
1015 static void rfcomm_multiplexer_set_state_and_request_can_send_now_event(rfcomm_multiplexer_t * multiplexer, RFCOMM_MULTIPLEXER_STATE state){
1016     multiplexer->state = state;
1017     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1018 }
1019 
1020 /**
1021  * @return handled packet
1022  */
1023 static int rfcomm_hci_event_handler(uint8_t *packet, uint16_t size){
1024 
1025     UNUSED(size);   // ok: handling own l2cap events
1026 
1027     bd_addr_t event_addr;
1028     uint16_t  psm;
1029     uint16_t l2cap_cid;
1030     hci_con_handle_t con_handle;
1031     rfcomm_multiplexer_t *multiplexer = NULL;
1032     uint8_t status;
1033 
1034     switch (hci_event_packet_get_type(packet)) {
1035 
1036         // accept incoming rfcomm connection if no multiplexer exists yet
1037         case L2CAP_EVENT_INCOMING_CONNECTION:
1038             // data: event(8), len(8), address(48), handle (16),  psm (16), source cid(16) dest cid(16)
1039             reverse_bd_addr(&packet[2], event_addr);
1040             con_handle = little_endian_read_16(packet,  8);
1041             psm        = little_endian_read_16(packet, 10);
1042             l2cap_cid  = little_endian_read_16(packet, 12);
1043 
1044             if (psm != BLUETOOTH_PROTOCOL_RFCOMM) break;
1045 
1046             multiplexer = rfcomm_multiplexer_for_addr(event_addr);
1047 
1048             if (multiplexer) {
1049                 log_info("INCOMING_CONNECTION (l2cap_cid 0x%02x) for BLUETOOTH_PROTOCOL_RFCOMM => decline - multiplexer already exists", l2cap_cid);
1050                 l2cap_decline_connection(l2cap_cid);
1051                 return 1;
1052             }
1053 
1054             // create and inititialize new multiplexer instance (incoming)
1055             multiplexer = rfcomm_multiplexer_create_for_addr(event_addr);
1056             if (!multiplexer){
1057                 log_info("INCOMING_CONNECTION (l2cap_cid 0x%02x) for BLUETOOTH_PROTOCOL_RFCOMM => decline - no memory left", l2cap_cid);
1058                 l2cap_decline_connection(l2cap_cid);
1059                 return 1;
1060             }
1061 
1062             multiplexer->con_handle = con_handle;
1063             multiplexer->l2cap_cid = l2cap_cid;
1064             //
1065             multiplexer->state = RFCOMM_MULTIPLEXER_W4_SABM_0;
1066             log_info("L2CAP_EVENT_INCOMING_CONNECTION (l2cap_cid 0x%02x) for BLUETOOTH_PROTOCOL_RFCOMM => accept", l2cap_cid);
1067 
1068 #ifdef RFCOMM_USE_ERTM
1069             // request
1070             rfcomm_ertm_request_t request;
1071             memset(&request, 0, sizeof(rfcomm_ertm_request_t));
1072             (void)memcpy(request.addr, event_addr, 6);
1073             request.ertm_id = rfcomm_next_ertm_id();
1074             if (rfcomm_ertm_request_callback){
1075                 (*rfcomm_ertm_request_callback)(&request);
1076             }
1077             if (request.ertm_config && request.ertm_buffer && request.ertm_buffer_size){
1078                 multiplexer->ertm_id = request.ertm_id;
1079                 l2cap_accept_ertm_connection(l2cap_cid, request.ertm_config, request.ertm_buffer, request.ertm_buffer_size);
1080                 return 1;
1081             }
1082 #endif
1083 
1084             l2cap_accept_connection(l2cap_cid);
1085             return 1;
1086 
1087         // l2cap connection opened -> store l2cap_cid, remote_addr
1088         case L2CAP_EVENT_CHANNEL_OPENED:
1089 
1090             if (little_endian_read_16(packet, 11) != BLUETOOTH_PROTOCOL_RFCOMM) break;
1091 
1092             status = packet[2];
1093             log_info("L2CAP_EVENT_CHANNEL_OPENED for BLUETOOTH_PROTOCOL_RFCOMM, status %u", status);
1094 
1095             // get multiplexer for remote addr
1096             con_handle = little_endian_read_16(packet, 9);
1097             l2cap_cid = little_endian_read_16(packet, 13);
1098             reverse_bd_addr(&packet[3], event_addr);
1099             multiplexer = rfcomm_multiplexer_for_addr(event_addr);
1100             if (!multiplexer) {
1101                 log_error("L2CAP_EVENT_CHANNEL_OPENED but no multiplexer prepared");
1102                 return 1;
1103             }
1104 
1105             // on l2cap open error discard everything
1106             if (status){
1107 
1108                 // remove (potential) timer
1109                 rfcomm_multiplexer_stop_timer(multiplexer);
1110 
1111                 // mark multiplexer as shutting down
1112                 multiplexer->state = RFCOMM_MULTIPLEXER_SHUTTING_DOWN;
1113 
1114                 // emit rfcomm_channel_opened with status and free channel
1115                 // note: repeatedly go over list until full iteration causes no further change
1116                 int done;
1117                 do {
1118                     done = 1;
1119                     btstack_linked_item_t * it = (btstack_linked_item_t *) &rfcomm_channels;
1120                     while (it->next) {
1121                         rfcomm_channel_t * channel = (rfcomm_channel_t *) it->next;
1122                         if (channel->multiplexer == multiplexer){
1123                             done = 0;
1124                             rfcomm_emit_channel_opened(channel, status);
1125                             btstack_linked_list_remove(&rfcomm_channels, (btstack_linked_item_t *) channel);
1126                             btstack_memory_rfcomm_channel_free(channel);
1127                             break;
1128                         } else {
1129                             it = it->next;
1130                         }
1131                     }
1132                 } while (!done);
1133 
1134                 // free multiplexer
1135                 rfcomm_multiplexer_free(multiplexer);
1136                 return 1;
1137             }
1138 
1139             // following could be: rfcom_multiplexer_state_machein(..., EVENT_L2CAP_OPENED)
1140 
1141             // set max frame size based on l2cap MTU
1142             multiplexer->max_frame_size = rfcomm_max_frame_size_for_l2cap_mtu(little_endian_read_16(packet, 17));
1143 
1144             if (multiplexer->state == RFCOMM_MULTIPLEXER_W4_CONNECT) {
1145                 log_info("L2CAP_EVENT_CHANNEL_OPENED: outgoing connection");
1146                 // wrong remote addr
1147                 if (bd_addr_cmp(event_addr, multiplexer->remote_addr)) break;
1148                 multiplexer->l2cap_cid = l2cap_cid;
1149                 multiplexer->con_handle = con_handle;
1150                 // send SABM #0
1151                 rfcomm_multiplexer_set_state_and_request_can_send_now_event(multiplexer, RFCOMM_MULTIPLEXER_SEND_SABM_0);
1152 
1153             }
1154             return 1;
1155 
1156             // l2cap disconnect -> state = RFCOMM_MULTIPLEXER_CLOSED;
1157 
1158         // Notify channel packet handler if they can send now
1159         case L2CAP_EVENT_CAN_SEND_NOW:
1160             l2cap_cid = l2cap_event_can_send_now_get_local_cid(packet);
1161             rfcomm_handle_can_send_now(l2cap_cid);
1162             return 1;
1163 
1164         case L2CAP_EVENT_CHANNEL_CLOSED:
1165             // data: event (8), len(8), channel (16)
1166             l2cap_cid = little_endian_read_16(packet, 2);
1167             multiplexer = rfcomm_multiplexer_for_l2cap_cid(l2cap_cid);
1168             log_info("L2CAP_EVENT_CHANNEL_CLOSED cid 0x%0x, mult %p", l2cap_cid, multiplexer);
1169             if (!multiplexer) break;
1170             log_info("L2CAP_EVENT_CHANNEL_CLOSED state %u", multiplexer->state);
1171             // no need to call l2cap_disconnect here, as it's already closed
1172             rfcomm_multiplexer_finalize(multiplexer);
1173             return 1;
1174 
1175 #ifdef RFCOMM_USE_ERTM
1176         case L2CAP_EVENT_ERTM_BUFFER_RELEASED:
1177             l2cap_cid = l2cap_event_ertm_buffer_released_get_local_cid(packet);
1178             multiplexer = rfcomm_multiplexer_for_l2cap_cid(l2cap_cid);
1179             if (multiplexer) {
1180                 log_info("buffer for ertm id %u released", multiplexer->ertm_id);
1181                 if (rfcomm_ertm_released_callback){
1182                     (*rfcomm_ertm_released_callback)(multiplexer->ertm_id);
1183                 }
1184             }
1185             break;
1186 #endif
1187 
1188         default:
1189             break;
1190     }
1191     return 0;
1192 }
1193 
1194 static int rfcomm_multiplexer_l2cap_packet_handler(uint16_t channel, uint8_t *packet, uint16_t size){
1195     // get or create a multiplexer for a certain device
1196     rfcomm_multiplexer_t *multiplexer = rfcomm_multiplexer_for_l2cap_cid(channel);
1197     if (!multiplexer) return 0;
1198 
1199     uint16_t l2cap_cid = multiplexer->l2cap_cid;
1200 
1201     if (size < 3) return 0;
1202 
1203 	// but only care for multiplexer control channel
1204     uint8_t frame_dlci = packet[0] >> 2;
1205     if (frame_dlci) return 0;
1206     const uint8_t length_offset = (packet[2] & 1) ^ 1;  // to be used for pos >= 3
1207     const uint8_t credit_offset = ((packet[1] & BT_RFCOMM_UIH_PF) == BT_RFCOMM_UIH_PF) ? 1 : 0;   // credits for uih_pf frames
1208     const uint8_t payload_offset = 3 + length_offset + credit_offset;
1209     switch (packet[1]){
1210 
1211         case BT_RFCOMM_SABM:
1212             if (multiplexer->state == RFCOMM_MULTIPLEXER_W4_SABM_0){
1213                 log_info("Received SABM #0");
1214                 multiplexer->outgoing = 0;
1215                 rfcomm_multiplexer_set_state_and_request_can_send_now_event(multiplexer, RFCOMM_MULTIPLEXER_SEND_UA_0);
1216                 return 1;
1217             }
1218             break;
1219 
1220         case BT_RFCOMM_UA:
1221             if (multiplexer->state == RFCOMM_MULTIPLEXER_W4_UA_0) {
1222                 // UA #0 -> send UA #0, state = RFCOMM_MULTIPLEXER_OPEN
1223                 log_info("Received UA #0 ");
1224                 rfcomm_multiplexer_opened(multiplexer);
1225                 return 1;
1226             }
1227             break;
1228 
1229         case BT_RFCOMM_DISC:
1230             // DISC #0 -> send UA #0, close multiplexer
1231             log_info("Received DISC #0, (ougoing = %u)", multiplexer->outgoing);
1232             rfcomm_multiplexer_set_state_and_request_can_send_now_event(multiplexer, RFCOMM_MULTIPLEXER_SEND_UA_0_AND_DISC);
1233             return 1;
1234 
1235         case BT_RFCOMM_DM:
1236             // DM #0 - we shouldn't get this, just give up
1237             log_info("Received DM #0");
1238             log_info("-> Closing down multiplexer");
1239             rfcomm_multiplexer_finalize(multiplexer);
1240             l2cap_disconnect(l2cap_cid, 0x13);
1241             return 1;
1242 
1243         case BT_RFCOMM_UIH:
1244             if (payload_offset >= size) return 0;
1245 
1246             if (packet[payload_offset] == BT_RFCOMM_CLD_CMD){
1247                 // Multiplexer close down (CLD) -> close mutliplexer
1248                 log_info("Received Multiplexer close down command");
1249                 log_info("-> Closing down multiplexer");
1250                 rfcomm_multiplexer_finalize(multiplexer);
1251                 l2cap_disconnect(l2cap_cid, 0x13);
1252                 return 1;
1253             }
1254             switch (packet[payload_offset]){
1255                 case BT_RFCOMM_CLD_CMD:
1256                      // Multiplexer close down (CLD) -> close mutliplexer
1257                     log_info("Received Multiplexer close down command");
1258                     log_info("-> Closing down multiplexer");
1259                     rfcomm_multiplexer_finalize(multiplexer);
1260                     l2cap_disconnect(l2cap_cid, 0x13);
1261                     return 1;
1262 
1263                 case BT_RFCOMM_FCON_CMD:
1264                     multiplexer->fcon = 0x81;
1265                     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1266                     return 1;
1267 
1268                 case BT_RFCOMM_FCOFF_CMD:
1269                     multiplexer->fcon = 0x80;
1270                     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1271                     return 1;
1272 
1273                 case BT_RFCOMM_TEST_CMD: {
1274                     if ((payload_offset + 1) >= size) return 0; // (1)
1275                     log_info("Received test command");
1276                     int len = packet[payload_offset+1] >> 1; // length < 125
1277                     if (len > RFCOMM_TEST_DATA_MAX_LEN){
1278                         len = RFCOMM_TEST_DATA_MAX_LEN;
1279                     }
1280                     // from (1) => (size - 1 - payload_offset) > 0
1281                     len = btstack_min(len, size - 1 - payload_offset);  // avoid information leak
1282                     multiplexer->test_data_len = len;
1283                     (void)memcpy(multiplexer->test_data,
1284                                  &packet[payload_offset + 2], len);
1285                     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1286                     return 1;
1287                 }
1288                 default:
1289                     break;
1290             }
1291             break;
1292 
1293         default:
1294             break;
1295 
1296     }
1297     return 0;
1298 }
1299 
1300 static int rfcomm_multiplexer_ready_to_send(rfcomm_multiplexer_t * multiplexer){
1301     if (multiplexer->send_dm_for_dlci) return 1;
1302     if (multiplexer->nsc_command) return 1;
1303     if (multiplexer->fcon & 0x80) return 1;
1304     switch (multiplexer->state){
1305         case RFCOMM_MULTIPLEXER_SEND_SABM_0:
1306         case RFCOMM_MULTIPLEXER_SEND_UA_0:
1307         case RFCOMM_MULTIPLEXER_SEND_UA_0_AND_DISC:
1308             return 1;
1309         case RFCOMM_MULTIPLEXER_OPEN:
1310             if (multiplexer->test_data_len) {
1311                 return 1;
1312             }
1313             break;
1314         default:
1315             break;
1316     }
1317     return 0;
1318 }
1319 
1320 static void rfcomm_multiplexer_state_machine(rfcomm_multiplexer_t * multiplexer, RFCOMM_MULTIPLEXER_EVENT event){
1321 
1322     if (event != MULT_EV_READY_TO_SEND) return;
1323 
1324     uint16_t l2cap_cid = multiplexer->l2cap_cid;
1325 
1326     // process stored DM responses
1327     if (multiplexer->send_dm_for_dlci){
1328         uint8_t dlci = multiplexer->send_dm_for_dlci;
1329         multiplexer->send_dm_for_dlci = 0;
1330         rfcomm_send_dm_pf(multiplexer, dlci);
1331         return;
1332     }
1333 
1334     if (multiplexer->nsc_command){
1335         uint8_t command = multiplexer->nsc_command;
1336         multiplexer->nsc_command = 0;
1337         rfcomm_send_uih_nsc_rsp(multiplexer, command);
1338         return;
1339     }
1340 
1341     if (multiplexer->fcon & 0x80){
1342         multiplexer->fcon &= 0x01;
1343         rfcomm_send_uih_fc_rsp(multiplexer, multiplexer->fcon);
1344 
1345         if (multiplexer->fcon == 0) return;
1346         // trigger client to send again after sending FCon Response
1347         rfcomm_notify_channel_can_send();
1348         return;
1349     }
1350 
1351     switch (multiplexer->state) {
1352         case RFCOMM_MULTIPLEXER_SEND_SABM_0:
1353             log_info("Sending SABM #0 - (multi 0x%p)", multiplexer);
1354             multiplexer->state = RFCOMM_MULTIPLEXER_W4_UA_0;
1355             rfcomm_send_sabm(multiplexer, 0);
1356             break;
1357         case RFCOMM_MULTIPLEXER_SEND_UA_0:
1358             log_info("Sending UA #0");
1359             multiplexer->state = RFCOMM_MULTIPLEXER_OPEN;
1360             rfcomm_send_ua(multiplexer, 0);
1361 
1362             rfcomm_multiplexer_opened(multiplexer);
1363             break;
1364         case RFCOMM_MULTIPLEXER_SEND_UA_0_AND_DISC:
1365             log_info("Sending UA #0");
1366             log_info("Closing down multiplexer");
1367             multiplexer->state = RFCOMM_MULTIPLEXER_CLOSED;
1368             rfcomm_send_ua(multiplexer, 0);
1369 
1370             rfcomm_multiplexer_finalize(multiplexer);
1371             l2cap_disconnect(l2cap_cid, 0x13);
1372             break;
1373         case RFCOMM_MULTIPLEXER_OPEN:
1374             // respond to test command
1375             if (multiplexer->test_data_len){
1376                 int len = multiplexer->test_data_len;
1377                 log_info("Sending TEST Response with %u bytes", len);
1378                 multiplexer->test_data_len = 0;
1379                 rfcomm_send_uih_test_rsp(multiplexer, multiplexer->test_data, len);
1380                 return;
1381             }
1382             break;
1383         default:
1384             break;
1385     }
1386 }
1387 
1388 // MARK: RFCOMM CHANNEL
1389 
1390 static void rfcomm_channel_send_credits(rfcomm_channel_t *channel, uint8_t credits){
1391     channel->credits_incoming += credits;
1392     rfcomm_send_uih_credits(channel->multiplexer, channel->dlci, credits);
1393 }
1394 
1395 static int rfcomm_channel_can_send(rfcomm_channel_t * channel){
1396     if (!channel->credits_outgoing) return 0;
1397     if ((channel->multiplexer->fcon & 1) == 0) return 0;
1398     return l2cap_can_send_packet_now(channel->multiplexer->l2cap_cid);
1399 }
1400 
1401 static void rfcomm_channel_opened(rfcomm_channel_t *rfChannel){
1402 
1403     log_info("rfcomm_channel_opened!");
1404 
1405     rfChannel->state = RFCOMM_CHANNEL_OPEN;
1406     rfcomm_emit_channel_opened(rfChannel, 0);
1407     rfcomm_emit_port_configuration(rfChannel);
1408 
1409     // remove (potential) timer
1410     rfcomm_multiplexer_t *multiplexer = rfChannel->multiplexer;
1411     if (multiplexer->timer_active) {
1412         btstack_run_loop_remove_timer(&multiplexer->timer);
1413         multiplexer->timer_active = 0;
1414     }
1415     // hack for problem detecting authentication failure
1416     multiplexer->at_least_one_connection = 1;
1417 
1418     // request can send now if channel ready
1419     if (rfcomm_channel_ready_to_send(rfChannel)){
1420         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1421     }
1422 }
1423 
1424 static void rfcomm_channel_packet_handler_uih(rfcomm_multiplexer_t *multiplexer, uint8_t * packet, uint16_t size){
1425     const uint8_t frame_dlci = packet[0] >> 2;
1426     const uint8_t length_offset = (packet[2] & 1) ^ 1;  // to be used for pos >= 3
1427     const uint8_t credit_offset = ((packet[1] & BT_RFCOMM_UIH_PF) == BT_RFCOMM_UIH_PF) ? 1 : 0;   // credits for uih_pf frames
1428     const uint8_t payload_offset = 3 + length_offset + credit_offset;
1429     int request_can_send_now = 0;
1430 
1431     rfcomm_channel_t * channel = rfcomm_channel_for_multiplexer_and_dlci(multiplexer, frame_dlci);
1432     if (!channel) return;
1433 
1434     // handle new outgoing credits
1435     if (packet[1] == BT_RFCOMM_UIH_PF) {
1436 
1437         // add them
1438         uint16_t new_credits = packet[3+length_offset];
1439         channel->credits_outgoing += new_credits;
1440         log_info( "RFCOMM data UIH_PF, new credits channel 0x%02x: %u, now %u", channel->rfcomm_cid, new_credits, channel->credits_outgoing);
1441 
1442         // notify channel statemachine
1443         rfcomm_channel_event_t channel_event = { CH_EVT_RCVD_CREDITS, 0 };
1444         log_debug("rfcomm_channel_state_machine_with_channel, waiting_for_can_send_now %u", channel->waiting_for_can_send_now);
1445         int rfcomm_channel_valid = 1;
1446         rfcomm_channel_state_machine_with_channel(channel, &channel_event, &rfcomm_channel_valid);
1447         if (rfcomm_channel_valid){
1448             if (rfcomm_channel_ready_to_send(channel) || channel->waiting_for_can_send_now){
1449                 request_can_send_now = 1;
1450             }
1451         }
1452     }
1453 
1454     // contains payload?
1455     if ((size - 1) > payload_offset){
1456 
1457         // log_info( "RFCOMM data UIH_PF, size %u, channel %p", size-payload_offset-1, rfChannel->connection);
1458 
1459         // decrease incoming credit counter
1460         if (channel->credits_incoming > 0){
1461             channel->credits_incoming--;
1462         }
1463 
1464         // deliver payload
1465         (channel->packet_handler)(RFCOMM_DATA_PACKET, channel->rfcomm_cid,
1466                               &packet[payload_offset], size-payload_offset-1);
1467     }
1468 
1469     // automatically provide new credits to remote device, if no incoming flow control
1470     if (!channel->incoming_flow_control && (channel->credits_incoming < 5)){
1471         channel->new_credits_incoming = RFCOMM_CREDITS;
1472         request_can_send_now = 1;
1473     }
1474 
1475     if (request_can_send_now){
1476         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1477     }
1478 }
1479 
1480 static void rfcomm_channel_accept_pn(rfcomm_channel_t *channel, rfcomm_channel_event_pn_t *event){
1481     // priority of client request
1482     channel->pn_priority = event->priority;
1483 
1484     // new credits
1485     channel->credits_outgoing = event->credits_outgoing;
1486 
1487     // negotiate max frame size
1488     if (channel->max_frame_size > channel->multiplexer->max_frame_size) {
1489         channel->max_frame_size = channel->multiplexer->max_frame_size;
1490     }
1491     if (channel->max_frame_size > event->max_frame_size) {
1492         channel->max_frame_size = event->max_frame_size;
1493     }
1494 
1495 }
1496 
1497 static void rfcomm_channel_finalize(rfcomm_channel_t *channel){
1498 
1499     rfcomm_multiplexer_t *multiplexer = channel->multiplexer;
1500 
1501     // remove from list
1502     btstack_linked_list_remove( &rfcomm_channels, (btstack_linked_item_t *) channel);
1503 
1504     // free channel
1505     btstack_memory_rfcomm_channel_free(channel);
1506 
1507     // update multiplexer timeout after channel was removed from list
1508     rfcomm_multiplexer_prepare_idle_timer(multiplexer);
1509 }
1510 
1511 static void rfcomm_channel_state_machine_with_dlci(rfcomm_multiplexer_t * multiplexer, uint8_t dlci, const rfcomm_channel_event_t *event){
1512 
1513     // TODO: if client max frame size is smaller than RFCOMM_DEFAULT_SIZE, send PN
1514 
1515 
1516     // lookup existing channel
1517     rfcomm_channel_t * channel = rfcomm_channel_for_multiplexer_and_dlci(multiplexer, dlci);
1518 
1519     // log_info("rfcomm_channel_state_machine_with_dlci lookup dlci #%u = 0x%08x - event %u", dlci, (int) channel, event->type);
1520 
1521     if (channel) {
1522         int rfcomm_channel_valid = 1;
1523         rfcomm_channel_state_machine_with_channel(channel, event, &rfcomm_channel_valid);
1524         if (rfcomm_channel_valid && rfcomm_channel_ready_to_send(channel)){
1525             l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1526         }
1527         return;
1528     }
1529 
1530     // service registered?
1531     rfcomm_service_t * service = rfcomm_service_for_channel(dlci >> 1);
1532     // log_info("rfcomm_channel_state_machine_with_dlci service dlci #%u = 0x%08x", dlci, (int) service);
1533     if (!service) {
1534         // discard request by sending disconnected mode
1535         multiplexer->send_dm_for_dlci = dlci;
1536         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1537         return;
1538     }
1539 
1540     // create channel for some events
1541     switch (event->type) {
1542         case CH_EVT_RCVD_SABM:
1543         case CH_EVT_RCVD_PN:
1544         case CH_EVT_RCVD_RPN_REQ:
1545         case CH_EVT_RCVD_RPN_CMD:
1546             // setup incoming channel
1547             channel = rfcomm_channel_create(multiplexer, service, dlci >> 1);
1548             if (!channel){
1549                 // discard request by sending disconnected mode
1550                 multiplexer->send_dm_for_dlci = dlci;
1551                 l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1552             }
1553             break;
1554         default:
1555             break;
1556     }
1557 
1558     if (!channel) {
1559         // discard request by sending disconnected mode
1560         multiplexer->send_dm_for_dlci = dlci;
1561         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1562         return;
1563     }
1564 
1565     int rfcomm_channel_valid = 1;
1566     rfcomm_channel_state_machine_with_channel(channel, event, &rfcomm_channel_valid);
1567     if (rfcomm_channel_valid && rfcomm_channel_ready_to_send(channel)){
1568         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1569     }
1570 }
1571 
1572 static void rfcomm_channel_packet_handler(rfcomm_multiplexer_t * multiplexer,  uint8_t *packet, uint16_t size){
1573 
1574     UNUSED(size);   // ok: fixed format messages
1575 
1576     // rfcomm: (0) addr [76543 server channel] [2 direction: initiator uses 1] [1 C/R: CMD by initiator = 1] [0 EA=1]
1577     const uint8_t frame_dlci = packet[0] >> 2;
1578     uint8_t message_dlci; // used by commands in UIH(_PF) packets
1579 	uint8_t message_len;  //   "
1580 
1581     // rfcomm: (1) command/control
1582     // -- credits_offset = 1 if command == BT_RFCOMM_UIH_PF
1583     const uint8_t credit_offset = ((packet[1] & BT_RFCOMM_UIH_PF) == BT_RFCOMM_UIH_PF) ? 1 : 0;   // credits for uih_pf frames
1584     // rfcomm: (2) length. if bit 0 is cleared, 2 byte length is used. (little endian)
1585     const uint8_t length_offset = (packet[2] & 1) ^ 1;  // to be used for pos >= 3
1586     // rfcomm: (3+length_offset) credits if credits_offset == 1
1587     // rfcomm: (3+length_offest+credits_offset)
1588     const uint8_t payload_offset = 3 + length_offset + credit_offset;
1589 
1590     rfcomm_channel_event_t event;
1591     rfcomm_channel_event_pn_t event_pn;
1592     rfcomm_channel_event_rpn_t event_rpn;
1593     rfcomm_channel_event_msc_t event_msc;
1594 
1595     // switch by rfcomm message type
1596     switch(packet[1]) {
1597 
1598         case BT_RFCOMM_SABM:
1599             event.type = CH_EVT_RCVD_SABM;
1600             log_info("Received SABM #%u", frame_dlci);
1601             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1602             break;
1603 
1604         case BT_RFCOMM_UA:
1605             event.type = CH_EVT_RCVD_UA;
1606             log_info("Received UA #%u",frame_dlci);
1607             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1608             break;
1609 
1610         case BT_RFCOMM_DISC:
1611             event.type = CH_EVT_RCVD_DISC;
1612             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1613             break;
1614 
1615         case BT_RFCOMM_DM:
1616         case BT_RFCOMM_DM_PF:
1617             event.type = CH_EVT_RCVD_DM;
1618             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1619             break;
1620 
1621         case BT_RFCOMM_UIH_PF:
1622         case BT_RFCOMM_UIH:
1623 
1624             message_len  = packet[payload_offset+1] >> 1;
1625 
1626             switch (packet[payload_offset]) {
1627                 case BT_RFCOMM_PN_CMD:
1628                     message_dlci = packet[payload_offset+2];
1629                     event_pn.super.type = CH_EVT_RCVD_PN;
1630                     event_pn.priority = packet[payload_offset+4];
1631                     event_pn.max_frame_size = little_endian_read_16(packet, payload_offset+6);
1632                     event_pn.credits_outgoing = packet[payload_offset+9];
1633                     log_info("Received UIH Parameter Negotiation Command for #%u, credits %u",
1634                         message_dlci, event_pn.credits_outgoing);
1635                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_pn);
1636                     break;
1637 
1638                 case BT_RFCOMM_PN_RSP:
1639                     message_dlci = packet[payload_offset+2];
1640                     event_pn.super.type = CH_EVT_RCVD_PN_RSP;
1641                     event_pn.priority = packet[payload_offset+4];
1642                     event_pn.max_frame_size = little_endian_read_16(packet, payload_offset+6);
1643                     event_pn.credits_outgoing = packet[payload_offset+9];
1644                     log_info("Received UIH Parameter Negotiation Response max frame %u, credits %u",
1645                             event_pn.max_frame_size, event_pn.credits_outgoing);
1646                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_pn);
1647                     break;
1648 
1649                 case BT_RFCOMM_MSC_CMD:
1650                     message_dlci = packet[payload_offset+2] >> 2;
1651                     event_msc.super.type = CH_EVT_RCVD_MSC_CMD;
1652                     event_msc.modem_status = packet[payload_offset+3];
1653                     log_info("Received MSC CMD for #%u, ", message_dlci);
1654                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_msc);
1655                     break;
1656 
1657                 case BT_RFCOMM_MSC_RSP:
1658                     message_dlci = packet[payload_offset+2] >> 2;
1659                     event.type = CH_EVT_RCVD_MSC_RSP;
1660                     log_info("Received MSC RSP for #%u", message_dlci);
1661                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, &event);
1662                     break;
1663 
1664                 case BT_RFCOMM_RPN_CMD:
1665                     message_dlci = packet[payload_offset+2] >> 2;
1666                     switch (message_len){
1667                         case 1:
1668                             log_info("Received Remote Port Negotiation Request for #%u", message_dlci);
1669                             event.type = CH_EVT_RCVD_RPN_REQ;
1670                             rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, &event);
1671                             break;
1672                         case 8:
1673                             log_info("Received Remote Port Negotiation Update for #%u", message_dlci);
1674                             event_rpn.super.type = CH_EVT_RCVD_RPN_CMD;
1675                             event_rpn.data = *(rfcomm_rpn_data_t*) &packet[payload_offset+3];
1676                             rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_rpn);
1677                             break;
1678                         default:
1679                             break;
1680                     }
1681                     break;
1682 
1683                 case BT_RFCOMM_RPN_RSP:
1684                     log_info("Received RPN response");
1685                     break;
1686 
1687                 case BT_RFCOMM_RLS_CMD: {
1688                     log_info("Received RLS command");
1689                     message_dlci = packet[payload_offset+2] >> 2;
1690                     rfcomm_channel_event_rls_t event_rls;
1691                     event_rls.super.type = CH_EVT_RCVD_RLS_CMD;
1692                     event_rls.line_status = packet[payload_offset+3];
1693                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_rls);
1694                     break;
1695                 }
1696 
1697                 case BT_RFCOMM_RLS_RSP:
1698                     log_info("Received RLS response");
1699                     break;
1700 
1701                 // Following commands are handled by rfcomm_multiplexer_l2cap_packet_handler
1702                 // case BT_RFCOMM_TEST_CMD:
1703                 // case BT_RFCOMM_FCOFF_CMD:
1704                 // case BT_RFCOMM_FCON_CMD:
1705                 // everything else is an not supported command
1706                 default: {
1707                     log_error("Received unknown UIH command packet - 0x%02x", packet[payload_offset]);
1708                     multiplexer->nsc_command = packet[payload_offset];
1709                     break;
1710                 }
1711             }
1712             break;
1713 
1714         default:
1715             log_error("Received unknown RFCOMM message type %x", packet[1]);
1716             break;
1717     }
1718 
1719     // trigger next action - example W4_PN_RSP: transition to SEND_SABM which only depends on "can send"
1720     if (rfcomm_multiplexer_ready_to_send(multiplexer)){
1721         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1722     }
1723 }
1724 
1725 static void rfcomm_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
1726 
1727     if (packet_type == HCI_EVENT_PACKET){
1728         rfcomm_hci_event_handler(packet, size);
1729         return;
1730     }
1731 
1732     // we only handle l2cap packets for:
1733     if (packet_type != L2CAP_DATA_PACKET) return;
1734 
1735     //  - multiplexer itself
1736     int handled = rfcomm_multiplexer_l2cap_packet_handler(channel, packet, size);
1737 
1738     if (handled) return;
1739 
1740     // - channel over open multiplexer
1741     rfcomm_multiplexer_t * multiplexer = rfcomm_multiplexer_for_l2cap_cid(channel);
1742     if ( (multiplexer == NULL) || (multiplexer->state != RFCOMM_MULTIPLEXER_OPEN)) return;
1743 
1744     // channel data ?
1745     // rfcomm: (0) addr [76543 server channel] [2 direction: initiator uses 1] [1 C/R: CMD by initiator = 1] [0 EA=1]
1746     const uint8_t frame_dlci = packet[0] >> 2;
1747 
1748     if (frame_dlci && ((packet[1] == BT_RFCOMM_UIH) || (packet[1] == BT_RFCOMM_UIH_PF))) {
1749         rfcomm_channel_packet_handler_uih(multiplexer, packet, size);
1750         return;
1751     }
1752 
1753     rfcomm_channel_packet_handler(multiplexer, packet, size);
1754 }
1755 
1756 static int rfcomm_channel_ready_for_open(rfcomm_channel_t *channel){
1757     // note: exchanging MSC isn't neccessary to consider channel open
1758     // note: having outgoing credits is also not necessary to consider channel open
1759     // log_info("rfcomm_channel_ready_for_open state %u, flags needed %04x, current %04x, rf credits %u, l2cap credits %u ", channel->state, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP|RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_RSP|RFCOMM_CHANNEL_STATE_VAR_SENT_CREDITS, channel->state_var, channel->credits_outgoing, channel->multiplexer->l2cap_credits);
1760     // if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_RSP) == 0) return 0;
1761     // if (channel->credits_outgoing == 0) return 0;
1762     log_info("rfcomm_channel_ready_for_open state %u, flags needed %04x, current %04x, rf credits %u",
1763          channel->state, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP, channel->state_var, channel->credits_outgoing);
1764     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP) == 0) return 0;
1765     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SENT_CREDITS) == 0) return 0;
1766 
1767     return 1;
1768 }
1769 
1770 static int rfcomm_channel_ready_for_incoming_dlc_setup(rfcomm_channel_t * channel){
1771     log_info("rfcomm_channel_ready_for_incoming_dlc_setup state var %04x", channel->state_var);
1772     // Client accept and SABM/UA is required, PN RSP is needed if PN was received
1773     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED) == 0) return 0;
1774     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM      ) == 0) return 0;
1775     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_UA        ) != 0) return 0;
1776     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP    ) != 0) return 0;
1777     return 1;
1778 }
1779 
1780 inline static void rfcomm_channel_state_add(rfcomm_channel_t *channel, RFCOMM_CHANNEL_STATE_VAR event){
1781     channel->state_var = (RFCOMM_CHANNEL_STATE_VAR) (channel->state_var | event);
1782 }
1783 inline static void rfcomm_channel_state_remove(rfcomm_channel_t *channel, RFCOMM_CHANNEL_STATE_VAR event){
1784     channel->state_var = (RFCOMM_CHANNEL_STATE_VAR) (channel->state_var & ~event);
1785 }
1786 
1787 static int rfcomm_channel_ready_to_send(rfcomm_channel_t * channel){
1788     switch (channel->state){
1789         case RFCOMM_CHANNEL_SEND_UIH_PN:
1790             log_debug("ch-ready: state %u", channel->state);
1791             return 1;
1792         case RFCOMM_CHANNEL_SEND_SABM_W4_UA:
1793             log_debug("ch-ready: state %u", channel->state);
1794             return 1;
1795         case RFCOMM_CHANNEL_SEND_UA_AFTER_DISC:
1796             log_debug("ch-ready: state %u", channel->state);
1797             return 1;
1798         case RFCOMM_CHANNEL_SEND_DISC:
1799             log_debug("ch-ready: state %u", channel->state);
1800             return 1;
1801         case RFCOMM_CHANNEL_SEND_DM:
1802             log_debug("ch-ready: state %u", channel->state);
1803             return 1;
1804         case RFCOMM_CHANNEL_OPEN:
1805             if (channel->new_credits_incoming) {
1806                 log_debug("ch-ready: channel open & new_credits_incoming") ;
1807                 return 1;
1808             }
1809             break;
1810         case RFCOMM_CHANNEL_DLC_SETUP:
1811             if (channel->state_var & (
1812                 RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD  |
1813                 RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS
1814              )) {
1815                 log_debug("ch-ready: channel dlc setup & send msc cmd or send credits") ;
1816                 return 1;
1817             }
1818             break;
1819 
1820         default:
1821             break;
1822     }
1823 
1824     if (channel->state_var & (
1825         RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP   |
1826         RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_INFO |
1827         RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP  |
1828         RFCOMM_CHANNEL_STATE_VAR_SEND_UA       |
1829         RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP
1830                              )){
1831         log_debug("ch-ready: state %x, state var %x", channel->state, channel->state_var);
1832         return 1;
1833     }
1834 
1835     if (channel->rls_line_status != RFCOMM_RLS_STATUS_INVALID) {
1836         log_debug("ch-ready: rls_line_status");
1837         return 1;
1838     }
1839 
1840     return 0;
1841 }
1842 
1843 
1844 static void rfcomm_channel_state_machine_with_channel(rfcomm_channel_t *channel, const rfcomm_channel_event_t *event, int * out_channel_valid){
1845 
1846     // log_info("rfcomm_channel_state_machine_with_channel: state %u, state_var %04x, event %u", channel->state, channel->state_var ,event->type);
1847 
1848     // channel != NULL -> channel valid
1849     *out_channel_valid = 1;
1850 
1851     rfcomm_multiplexer_t *multiplexer = channel->multiplexer;
1852 
1853     // TODO: integrate in common switch
1854     if (event->type == CH_EVT_RCVD_DISC){
1855         rfcomm_emit_channel_closed(channel);
1856         channel->state = RFCOMM_CHANNEL_SEND_UA_AFTER_DISC;
1857         return;
1858     }
1859 
1860     // TODO: integrate in common switch
1861     if (event->type == CH_EVT_RCVD_DM){
1862         log_info("Received DM message for #%u", channel->dlci);
1863         log_info("-> Closing channel locally for #%u", channel->dlci);
1864         rfcomm_channel_emit_final_event(channel, ERROR_CODE_CONNECTION_REJECTED_DUE_TO_LIMITED_RESOURCES);
1865         rfcomm_channel_finalize(channel);
1866         *out_channel_valid = 0;
1867         return;
1868     }
1869 
1870     // remote port negotiation command - just accept everything for now
1871     //
1872     // "The RPN command can be used before a new DLC is opened and should be used whenever the port settings change."
1873     // "The RPN command is specified as optional in TS 07.10, but it is mandatory to recognize and respond to it in RFCOMM.
1874     //   (Although the handling of individual settings are implementation-dependent.)"
1875     //
1876 
1877     // TODO: integrate in common switch
1878     if (event->type == CH_EVT_RCVD_RPN_CMD){
1879         // control port parameters
1880         rfcomm_channel_event_rpn_t *event_rpn = (rfcomm_channel_event_rpn_t*) event;
1881         rfcomm_rpn_data_update(&channel->rpn_data, &event_rpn->data);
1882         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP);
1883         // notify client about new settings
1884         rfcomm_emit_port_configuration(channel);
1885         return;
1886     }
1887 
1888     // TODO: integrate in common switch
1889     if (event->type == CH_EVT_RCVD_RPN_REQ){
1890         // no values got accepted (no values have beens sent)
1891         channel->rpn_data.parameter_mask_0 = 0x00;
1892         channel->rpn_data.parameter_mask_1 = 0x00;
1893         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP);
1894         return;
1895     }
1896 
1897     if (event->type == CH_EVT_RCVD_RLS_CMD){
1898         rfcomm_channel_event_rls_t * event_rls = (rfcomm_channel_event_rls_t*) event;
1899         channel->rls_line_status = event_rls->line_status & 0x0f;
1900         log_info("CH_EVT_RCVD_RLS_CMD setting line status to 0x%0x", channel->rls_line_status);
1901         rfcomm_emit_remote_line_status(channel, event_rls->line_status);
1902         return;
1903     }
1904 
1905     // TODO: integrate in common switch
1906     if (event->type == CH_EVT_READY_TO_SEND){
1907         if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP){
1908             log_info("Sending Remote Port Negotiation RSP for #%u", channel->dlci);
1909             rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP);
1910             rfcomm_send_uih_rpn_rsp(multiplexer, channel->dlci, &channel->rpn_data);
1911             return;
1912         }
1913         if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP){
1914             log_info("Sending MSC RSP for #%u", channel->dlci);
1915             rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP);
1916             rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_RSP);
1917             rfcomm_send_uih_msc_rsp(multiplexer, channel->dlci, 0x8d);  // ea=1,fc=0,rtc=1,rtr=1,ic=0,dv=1
1918             return;
1919         }
1920         if (channel->rls_line_status != RFCOMM_RLS_STATUS_INVALID){
1921             log_info("Sending RLS RSP 0x%0x", channel->rls_line_status);
1922             uint8_t line_status = channel->rls_line_status;
1923             channel->rls_line_status = RFCOMM_RLS_STATUS_INVALID;
1924             rfcomm_send_uih_rls_rsp(multiplexer, channel->dlci, line_status);
1925             return;
1926         }
1927     }
1928 
1929     // emit MSC status to app
1930     if (event->type == CH_EVT_RCVD_MSC_CMD){
1931         // notify client about new settings
1932         rfcomm_channel_event_msc_t *event_msc = (rfcomm_channel_event_msc_t*) event;
1933         uint8_t modem_status_event[2+1];
1934         modem_status_event[0] = RFCOMM_EVENT_REMOTE_MODEM_STATUS;
1935         modem_status_event[1] = 1;
1936         modem_status_event[2] = event_msc->modem_status;
1937         (channel->packet_handler)(HCI_EVENT_PACKET, channel->rfcomm_cid, (uint8_t*)&modem_status_event, sizeof(modem_status_event));
1938         // no return, MSC_CMD will be handled by state machine below
1939     }
1940 
1941     rfcomm_channel_event_pn_t * event_pn = (rfcomm_channel_event_pn_t*) event;
1942 
1943     switch (channel->state) {
1944         case RFCOMM_CHANNEL_CLOSED:
1945             switch (event->type){
1946                 case CH_EVT_RCVD_SABM:
1947                     log_info("-> Inform app");
1948                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM);
1949                     channel->state = RFCOMM_CHANNEL_INCOMING_SETUP;
1950                     rfcomm_emit_connection_request(channel);
1951                     break;
1952                 case CH_EVT_RCVD_PN:
1953                     rfcomm_channel_accept_pn(channel, event_pn);
1954                     log_info("-> Inform app");
1955                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_PN);
1956                     channel->state = RFCOMM_CHANNEL_INCOMING_SETUP;
1957                     rfcomm_emit_connection_request(channel);
1958                     break;
1959                 default:
1960                     break;
1961             }
1962             break;
1963 
1964         case RFCOMM_CHANNEL_INCOMING_SETUP:
1965             switch (event->type){
1966                 case CH_EVT_RCVD_SABM:
1967                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM);
1968                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED) {
1969                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_UA);
1970                     }
1971                     break;
1972                 case CH_EVT_RCVD_PN:
1973                     rfcomm_channel_accept_pn(channel, event_pn);
1974                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_PN);
1975                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED) {
1976                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP);
1977                     }
1978                     break;
1979                 case CH_EVT_READY_TO_SEND:
1980                     // if / else if is used to check for state transition after sending
1981                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP){
1982                         log_info("Sending UIH Parameter Negotiation Respond for #%u", channel->dlci);
1983                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP);
1984                         rfcomm_send_uih_pn_response(multiplexer, channel->dlci, channel->pn_priority, channel->max_frame_size);
1985                     } else if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_UA){
1986                         log_info("Sending UA #%u", channel->dlci);
1987                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_UA);
1988                         rfcomm_send_ua(multiplexer, channel->dlci);
1989                     }
1990                     if (rfcomm_channel_ready_for_incoming_dlc_setup(channel)){
1991                         log_info("Incomping setup done, requesting send MSC CMD and send Credits");
1992                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD);
1993                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS);
1994                         channel->state = RFCOMM_CHANNEL_DLC_SETUP;
1995                      }
1996                     break;
1997                 default:
1998                     break;
1999             }
2000             break;
2001 
2002         case RFCOMM_CHANNEL_W4_MULTIPLEXER:
2003             switch (event->type) {
2004                 case CH_EVT_MULTIPLEXER_READY:
2005                     log_info("Muliplexer opened, sending UIH PN next");
2006                     channel->state = RFCOMM_CHANNEL_SEND_UIH_PN;
2007                     break;
2008                 default:
2009                     break;
2010             }
2011             break;
2012 
2013         case RFCOMM_CHANNEL_SEND_UIH_PN:
2014             switch (event->type) {
2015                 case CH_EVT_READY_TO_SEND:
2016                     // update mtu
2017                     channel->max_frame_size = btstack_min(multiplexer->max_frame_size, channel->max_frame_size);
2018                     log_info("Sending UIH Parameter Negotiation Command for #%u (channel 0x%p) mtu %u", channel->dlci, channel, channel->max_frame_size );
2019                     channel->state = RFCOMM_CHANNEL_W4_PN_RSP;
2020                     rfcomm_send_uih_pn_command(multiplexer, channel->dlci, channel->max_frame_size);
2021                     break;
2022                 default:
2023                     break;
2024             }
2025             break;
2026 
2027         case RFCOMM_CHANNEL_W4_PN_RSP:
2028             switch (event->type){
2029                 case CH_EVT_RCVD_PN_RSP:
2030                     // update max frame size
2031                     if (channel->max_frame_size > event_pn->max_frame_size) {
2032                         channel->max_frame_size = event_pn->max_frame_size;
2033                     }
2034                     // new credits
2035                     channel->credits_outgoing = event_pn->credits_outgoing;
2036                     channel->state = RFCOMM_CHANNEL_SEND_SABM_W4_UA;
2037                     break;
2038                 default:
2039                     break;
2040             }
2041             break;
2042 
2043         case RFCOMM_CHANNEL_SEND_SABM_W4_UA:
2044             switch (event->type) {
2045                 case CH_EVT_READY_TO_SEND:
2046                     log_info("Sending SABM #%u", channel->dlci);
2047                     channel->state = RFCOMM_CHANNEL_W4_UA;
2048                     rfcomm_send_sabm(multiplexer, channel->dlci);
2049                     break;
2050                 default:
2051                     break;
2052             }
2053             break;
2054 
2055         case RFCOMM_CHANNEL_W4_UA:
2056             switch (event->type){
2057                 case CH_EVT_RCVD_UA:
2058                     channel->state = RFCOMM_CHANNEL_DLC_SETUP;
2059                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD);
2060                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS);
2061                     break;
2062                 default:
2063                     break;
2064             }
2065             break;
2066 
2067         case RFCOMM_CHANNEL_DLC_SETUP:
2068             switch (event->type){
2069                 case CH_EVT_RCVD_MSC_CMD:
2070                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_CMD);
2071                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP);
2072                     break;
2073                 case CH_EVT_RCVD_MSC_RSP:
2074                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP);
2075                     break;
2076 
2077                 case CH_EVT_READY_TO_SEND:
2078                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD){
2079                         log_info("Sending MSC CMD for #%u", channel->dlci);
2080                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD);
2081                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_CMD);
2082                         rfcomm_send_uih_msc_cmd(multiplexer, channel->dlci , 0x8d);  // ea=1,fc=0,rtc=1,rtr=1,ic=0,dv=1
2083                         break;
2084                     }
2085                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS){
2086                         log_info("Providing credits for #%u", channel->dlci);
2087                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS);
2088                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SENT_CREDITS);
2089 
2090                         if (channel->new_credits_incoming) {
2091                             uint8_t new_credits = channel->new_credits_incoming;
2092                             channel->new_credits_incoming = 0;
2093                             rfcomm_channel_send_credits(channel, new_credits);
2094                         }
2095                         break;
2096 
2097                     }
2098                     break;
2099                 default:
2100                     break;
2101             }
2102             // finally done?
2103             if (rfcomm_channel_ready_for_open(channel)){
2104                 channel->state = RFCOMM_CHANNEL_OPEN;
2105                 rfcomm_channel_opened(channel);
2106             }
2107             break;
2108 
2109         case RFCOMM_CHANNEL_OPEN:
2110             switch (event->type){
2111                 case CH_EVT_RCVD_MSC_CMD:
2112                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP);
2113                     break;
2114                 case CH_EVT_READY_TO_SEND:
2115                     if (channel->new_credits_incoming) {
2116                         uint8_t new_credits = channel->new_credits_incoming;
2117                         channel->new_credits_incoming = 0;
2118                         rfcomm_channel_send_credits(channel, new_credits);
2119                         break;
2120                     }
2121                     break;
2122                 case CH_EVT_RCVD_CREDITS:
2123                     rfcomm_notify_channel_can_send();
2124                     break;
2125                 default:
2126                     break;
2127             }
2128             break;
2129 
2130         case RFCOMM_CHANNEL_SEND_DM:
2131             switch (event->type) {
2132                 case CH_EVT_READY_TO_SEND:
2133                     log_info("Sending DM_PF for #%u", channel->dlci);
2134                     // don't emit channel closed - channel was never open
2135                     channel->state = RFCOMM_CHANNEL_CLOSED;
2136                     rfcomm_send_dm_pf(multiplexer, channel->dlci);
2137                     rfcomm_channel_finalize(channel);
2138                     *out_channel_valid = 0;
2139                     break;
2140                 default:
2141                     break;
2142             }
2143             break;
2144 
2145         case RFCOMM_CHANNEL_SEND_DISC:
2146             switch (event->type) {
2147                 case CH_EVT_READY_TO_SEND:
2148                     channel->state = RFCOMM_CHANNEL_W4_UA_AFTER_DISC;
2149                     rfcomm_send_disc(multiplexer, channel->dlci);
2150                     break;
2151                 default:
2152                     break;
2153             }
2154             break;
2155 
2156         case RFCOMM_CHANNEL_W4_UA_AFTER_DISC:
2157             switch (event->type){
2158                 case CH_EVT_RCVD_UA:
2159                     channel->state = RFCOMM_CHANNEL_CLOSED;
2160                     rfcomm_emit_channel_closed(channel);
2161                     rfcomm_channel_finalize(channel);
2162                     *out_channel_valid = 0;
2163                     break;
2164                 default:
2165                     break;
2166             }
2167             break;
2168 
2169         case RFCOMM_CHANNEL_SEND_UA_AFTER_DISC:
2170             switch (event->type) {
2171                 case CH_EVT_READY_TO_SEND:
2172                     log_info("Sending UA after DISC for #%u", channel->dlci);
2173                     channel->state = RFCOMM_CHANNEL_CLOSED;
2174                     rfcomm_send_ua(multiplexer, channel->dlci);
2175                     rfcomm_channel_finalize(channel);
2176                     *out_channel_valid = 0;
2177                     break;
2178                 default:
2179                     break;
2180             }
2181             break;
2182 
2183         default:
2184             break;
2185     }
2186 }
2187 
2188 // MARK: RFCOMM BTstack API
2189 
2190 void rfcomm_init(void){
2191     rfcomm_client_cid_generator = 0;
2192     rfcomm_multiplexers = NULL;
2193     rfcomm_services     = NULL;
2194     rfcomm_channels     = NULL;
2195     rfcomm_security_level = gap_get_security_level();
2196 #ifdef RFCOMM_USE_ERTM
2197     rfcomm_ertm_id = 0;
2198 #endif
2199 }
2200 
2201 void rfcomm_deinit(void){
2202 #ifdef RFCOMM_USE_ERTM
2203     rfcomm_ertm_request_callback  = NULL;
2204     rfcomm_ertm_released_callback = NULL;
2205 #endif
2206 }
2207 
2208 void rfcomm_set_required_security_level(gap_security_level_t security_level){
2209     rfcomm_security_level = security_level;
2210 }
2211 
2212 int rfcomm_can_send_packet_now(uint16_t rfcomm_cid){
2213     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2214     if (!channel){
2215         log_error("rfcomm_send cid 0x%02x doesn't exist!", rfcomm_cid);
2216         return 0;
2217     }
2218     return rfcomm_channel_can_send(channel);
2219 }
2220 
2221 void rfcomm_request_can_send_now_event(uint16_t rfcomm_cid){
2222     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2223     if (!channel){
2224         log_error("rfcomm_send cid 0x%02x doesn't exist!", rfcomm_cid);
2225         return;
2226     }
2227     channel->waiting_for_can_send_now = 1;
2228     l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2229 }
2230 
2231 static int rfcomm_assert_send_valid(rfcomm_channel_t * channel , uint16_t len){
2232     if (len > channel->max_frame_size){
2233         log_error("rfcomm_send cid 0x%02x, rfcomm data lenght exceeds MTU!", channel->rfcomm_cid);
2234         return RFCOMM_DATA_LEN_EXCEEDS_MTU;
2235     }
2236 
2237 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2238     if (len > rfcomm_max_frame_size_for_l2cap_mtu(sizeof(outgoing_buffer))){
2239         log_error("rfcomm_send cid 0x%02x, length exceeds outgoing rfcomm_out_buffer", channel->rfcomm_cid);
2240         return RFCOMM_DATA_LEN_EXCEEDS_MTU;
2241     }
2242 #endif
2243 
2244     if (!channel->credits_outgoing){
2245         log_info("rfcomm_send cid 0x%02x, no rfcomm outgoing credits!", channel->rfcomm_cid);
2246         return RFCOMM_NO_OUTGOING_CREDITS;
2247     }
2248 
2249     if ((channel->multiplexer->fcon & 1) == 0){
2250         log_info("rfcomm_send cid 0x%02x, aggregate flow off!", channel->rfcomm_cid);
2251         return RFCOMM_AGGREGATE_FLOW_OFF;
2252     }
2253     return 0;
2254 }
2255 
2256 uint16_t rfcomm_get_max_frame_size(uint16_t rfcomm_cid){
2257     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2258     if (!channel){
2259         log_error("rfcomm_get_max_frame_size cid 0x%02x doesn't exist!", rfcomm_cid);
2260         return 0;
2261     }
2262     return channel->max_frame_size;
2263 }
2264 
2265 // pre: rfcomm_can_send_packet_now(rfcomm_cid) == true
2266 int rfcomm_reserve_packet_buffer(void){
2267 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2268     log_error("rfcomm_reserve_packet_buffer should not get called with ERTM");
2269     return 0;
2270 #else
2271     return l2cap_reserve_packet_buffer();
2272 #endif
2273 }
2274 
2275 void rfcomm_release_packet_buffer(void){
2276 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2277     log_error("rfcomm_release_packet_buffer should not get called with ERTM");
2278 #else
2279     l2cap_release_packet_buffer();
2280 #endif
2281 }
2282 
2283 uint8_t * rfcomm_get_outgoing_buffer(void){
2284 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2285     uint8_t * rfcomm_out_buffer = outgoing_buffer;
2286 #else
2287     uint8_t * rfcomm_out_buffer = l2cap_get_outgoing_buffer();
2288 #endif
2289     // address + control + length (16) + no credit field
2290     return &rfcomm_out_buffer[4];
2291 }
2292 
2293 int rfcomm_send_prepared(uint16_t rfcomm_cid, uint16_t len){
2294     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2295     if (!channel){
2296         log_error("rfcomm_send_prepared cid 0x%02x doesn't exist!", rfcomm_cid);
2297         return 0;
2298     }
2299 
2300     int err = rfcomm_assert_send_valid(channel, len);
2301     if (err) return err;
2302 
2303 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2304     if (!l2cap_can_send_packet_now(channel->multiplexer->l2cap_cid)){
2305         log_error("rfcomm_send_prepared: l2cap cannot send now");
2306         return BTSTACK_ACL_BUFFERS_FULL;
2307     }
2308 #else
2309     if (!l2cap_can_send_prepared_packet_now(channel->multiplexer->l2cap_cid)){
2310         log_error("rfcomm_send_prepared: l2cap cannot send now");
2311         return BTSTACK_ACL_BUFFERS_FULL;
2312     }
2313 #endif
2314 
2315     // send might cause l2cap to emit new credits, update counters first
2316     if (len){
2317         channel->credits_outgoing--;
2318     } else {
2319         log_info("sending empty RFCOMM packet for cid %02x", rfcomm_cid);
2320     }
2321 
2322     int result = rfcomm_send_uih_prepared(channel->multiplexer, channel->dlci, len);
2323 
2324     if (result != 0) {
2325         if (len) {
2326             channel->credits_outgoing++;
2327         }
2328         log_error("rfcomm_send_prepared: error %d", result);
2329         return result;
2330     }
2331 
2332     return result;
2333 }
2334 
2335 int rfcomm_send(uint16_t rfcomm_cid, uint8_t *data, uint16_t len){
2336     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2337     if (!channel){
2338         log_error("cid 0x%02x doesn't exist!", rfcomm_cid);
2339         return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
2340     }
2341 
2342     int err = rfcomm_assert_send_valid(channel, len);
2343     if (err) return err;
2344     if (!l2cap_can_send_packet_now(channel->multiplexer->l2cap_cid)){
2345         log_error("rfcomm_send_internal: l2cap cannot send now");
2346         return BTSTACK_ACL_BUFFERS_FULL;
2347     }
2348 
2349 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2350 #else
2351     rfcomm_reserve_packet_buffer();
2352 #endif
2353     uint8_t * rfcomm_payload = rfcomm_get_outgoing_buffer();
2354 
2355     (void)memcpy(rfcomm_payload, data, len);
2356     err = rfcomm_send_prepared(rfcomm_cid, len);
2357 
2358 #ifdef RFCOMM_USE_OUTGOING_BUFFER
2359 #else
2360     if (err){
2361         rfcomm_release_packet_buffer();
2362     }
2363 #endif
2364 
2365     return err;
2366 }
2367 
2368 // Sends Local Lnie Status, see LINE_STATUS_..
2369 int rfcomm_send_local_line_status(uint16_t rfcomm_cid, uint8_t line_status){
2370     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2371     if (!channel){
2372         log_error("rfcomm_send_local_line_status cid 0x%02x doesn't exist!", rfcomm_cid);
2373         return 0;
2374     }
2375     return rfcomm_send_uih_rls_cmd(channel->multiplexer, channel->dlci, line_status);
2376 }
2377 
2378 // Sned local modem status. see MODEM_STAUS_..
2379 int rfcomm_send_modem_status(uint16_t rfcomm_cid, uint8_t modem_status){
2380     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2381     if (!channel){
2382         log_error("rfcomm_send_modem_status cid 0x%02x doesn't exist!", rfcomm_cid);
2383         return 0;
2384     }
2385     return rfcomm_send_uih_msc_cmd(channel->multiplexer, channel->dlci, modem_status);
2386 }
2387 
2388 // Configure remote port
2389 int rfcomm_send_port_configuration(uint16_t rfcomm_cid, rpn_baud_t baud_rate, rpn_data_bits_t data_bits, rpn_stop_bits_t stop_bits, rpn_parity_t parity, rpn_flow_control_t flow_control){
2390     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2391     if (!channel){
2392         log_error("rfcomm_send_port_configuration cid 0x%02x doesn't exist!", rfcomm_cid);
2393         return 0;
2394     }
2395     rfcomm_rpn_data_t rpn_data;
2396     rpn_data.baud_rate = baud_rate;
2397     rpn_data.flags = data_bits | (stop_bits << 2) | (parity << 3);
2398     rpn_data.flow_control = flow_control;
2399     rpn_data.xon = 0;
2400     rpn_data.xoff = 0;
2401     rpn_data.parameter_mask_0 = 0x1f;   // all but xon/xoff
2402     rpn_data.parameter_mask_1 = 0x3f;   // all flow control options
2403     return rfcomm_send_uih_rpn_cmd(channel->multiplexer, channel->dlci, &rpn_data);
2404 }
2405 
2406 // Query remote port
2407 int rfcomm_query_port_configuration(uint16_t rfcomm_cid){
2408     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2409     if (!channel){
2410         log_error("rfcomm_query_port_configuration cid 0x%02x doesn't exist!", rfcomm_cid);
2411         return 0;
2412     }
2413     return rfcomm_send_uih_rpn_req(channel->multiplexer, channel->dlci);
2414 }
2415 
2416 
2417 static uint8_t rfcomm_channel_create_internal(btstack_packet_handler_t packet_handler, bd_addr_t addr, uint8_t server_channel, uint8_t incoming_flow_control, uint8_t initial_credits, uint16_t * out_rfcomm_cid){
2418     log_info("RFCOMM_CREATE_CHANNEL addr %s channel #%u init credits %u",  bd_addr_to_str(addr), server_channel, initial_credits);
2419 
2420     // create new multiplexer if necessary
2421     uint8_t status = 0;
2422     uint8_t dlci = 0;
2423     int new_multiplexer = 0;
2424     rfcomm_channel_t * channel = NULL;
2425     rfcomm_multiplexer_t * multiplexer = rfcomm_multiplexer_for_addr(addr);
2426     if (!multiplexer) {
2427         multiplexer = rfcomm_multiplexer_create_for_addr(addr);
2428         if (!multiplexer) return BTSTACK_MEMORY_ALLOC_FAILED;
2429 
2430         multiplexer->outgoing = 1;
2431         multiplexer->state = RFCOMM_MULTIPLEXER_W4_CONNECT;
2432         new_multiplexer = 1;
2433     }
2434 
2435     // check if channel for this remote service already exists
2436     dlci = (server_channel << 1) | (multiplexer->outgoing ^ 1);
2437     channel = rfcomm_channel_for_multiplexer_and_dlci(multiplexer, dlci);
2438     if (channel){
2439         if (new_multiplexer) btstack_memory_rfcomm_multiplexer_free(multiplexer);
2440         return RFCOMM_CHANNEL_ALREADY_REGISTERED;
2441     }
2442 
2443     // prepare channel
2444     channel = rfcomm_channel_create(multiplexer, NULL, server_channel);
2445     if (!channel){
2446         if (new_multiplexer) btstack_memory_rfcomm_multiplexer_free(multiplexer);
2447         return BTSTACK_MEMORY_ALLOC_FAILED;
2448     }
2449 
2450     // rfcomm_cid is already assigned by rfcomm_channel_create
2451     channel->incoming_flow_control = incoming_flow_control;
2452     channel->new_credits_incoming  = initial_credits;
2453     channel->packet_handler = packet_handler;
2454 
2455     // return rfcomm_cid
2456     if (out_rfcomm_cid){
2457         *out_rfcomm_cid = channel->rfcomm_cid;
2458     }
2459 
2460     // start multiplexer setup
2461     if (multiplexer->state != RFCOMM_MULTIPLEXER_OPEN) {
2462         channel->state = RFCOMM_CHANNEL_W4_MULTIPLEXER;
2463         uint16_t l2cap_cid = 0;
2464 #ifdef RFCOMM_USE_ERTM
2465         // request
2466         rfcomm_ertm_request_t request;
2467         memset(&request, 0, sizeof(rfcomm_ertm_request_t));
2468         (void)memcpy(request.addr, addr, 6);
2469         request.ertm_id = rfcomm_next_ertm_id();
2470         if (rfcomm_ertm_request_callback){
2471             (*rfcomm_ertm_request_callback)(&request);
2472         }
2473         if (request.ertm_config && request.ertm_buffer && request.ertm_buffer_size){
2474             multiplexer->ertm_id = request.ertm_id;
2475             status = l2cap_create_ertm_channel(rfcomm_packet_handler, addr, BLUETOOTH_PROTOCOL_RFCOMM,
2476                         request.ertm_config, request.ertm_buffer, request.ertm_buffer_size, &l2cap_cid);
2477         }
2478         else
2479 #endif
2480         {
2481             status = l2cap_create_channel(rfcomm_packet_handler, addr, BLUETOOTH_PROTOCOL_RFCOMM, l2cap_max_mtu(), &l2cap_cid);
2482         }
2483         if (status) {
2484             if (new_multiplexer) btstack_memory_rfcomm_multiplexer_free(multiplexer);
2485             btstack_memory_rfcomm_channel_free(channel);
2486             return status;
2487         }
2488         multiplexer->l2cap_cid = l2cap_cid;
2489         return ERROR_CODE_SUCCESS;
2490     }
2491 
2492     channel->state = RFCOMM_CHANNEL_SEND_UIH_PN;
2493 
2494     // start connecting, if multiplexer is already up and running
2495     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
2496     return ERROR_CODE_SUCCESS;
2497 }
2498 
2499 uint8_t rfcomm_create_channel_with_initial_credits(btstack_packet_handler_t packet_handler, bd_addr_t addr, uint8_t server_channel, uint8_t initial_credits, uint16_t * out_rfcomm_cid){
2500     return rfcomm_channel_create_internal(packet_handler, addr, server_channel, 1, initial_credits, out_rfcomm_cid);
2501 }
2502 
2503 uint8_t rfcomm_create_channel(btstack_packet_handler_t packet_handler, bd_addr_t addr, uint8_t server_channel, uint16_t * out_rfcomm_cid){
2504     return rfcomm_channel_create_internal(packet_handler, addr, server_channel, 0, RFCOMM_CREDITS, out_rfcomm_cid);
2505 }
2506 
2507 void rfcomm_disconnect(uint16_t rfcomm_cid){
2508     log_info("RFCOMM_DISCONNECT cid 0x%02x", rfcomm_cid);
2509     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2510     if (!channel) return;
2511 
2512     channel->state = RFCOMM_CHANNEL_SEND_DISC;
2513     l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2514 }
2515 
2516 static uint8_t rfcomm_register_service_internal(btstack_packet_handler_t packet_handler,
2517     uint8_t channel, uint16_t max_frame_size, uint8_t incoming_flow_control, uint8_t initial_credits){
2518 
2519     log_info("RFCOMM_REGISTER_SERVICE channel #%u mtu %u flow_control %u credits %u",
2520              channel, max_frame_size, incoming_flow_control, initial_credits);
2521 
2522     // check if already registered
2523     rfcomm_service_t * service = rfcomm_service_for_channel(channel);
2524     if (service){
2525         return RFCOMM_CHANNEL_ALREADY_REGISTERED;
2526     }
2527 
2528     // alloc structure
2529     service = btstack_memory_rfcomm_service_get();
2530     if (!service) {
2531         return BTSTACK_MEMORY_ALLOC_FAILED;
2532     }
2533 
2534     // register with l2cap if not registered before, max MTU
2535     if (btstack_linked_list_empty(&rfcomm_services)){
2536         l2cap_register_service(rfcomm_packet_handler, BLUETOOTH_PROTOCOL_RFCOMM, 0xffff, rfcomm_security_level);
2537     }
2538 
2539     // fill in
2540     service->packet_handler = packet_handler;
2541     service->server_channel = channel;
2542     service->max_frame_size = max_frame_size;
2543     service->incoming_flow_control = incoming_flow_control;
2544     service->incoming_initial_credits = initial_credits;
2545 
2546     // add to services list
2547     btstack_linked_list_add(&rfcomm_services, (btstack_linked_item_t *) service);
2548 
2549     return 0;
2550 }
2551 
2552 uint8_t rfcomm_register_service_with_initial_credits(btstack_packet_handler_t packet_handler,
2553     uint8_t channel, uint16_t max_frame_size, uint8_t initial_credits){
2554 
2555     return rfcomm_register_service_internal(packet_handler, channel, max_frame_size, 1, initial_credits);
2556 }
2557 
2558 uint8_t rfcomm_register_service(btstack_packet_handler_t packet_handler, uint8_t channel,
2559     uint16_t max_frame_size){
2560 
2561     return rfcomm_register_service_internal(packet_handler, channel, max_frame_size, 0,RFCOMM_CREDITS);
2562 }
2563 
2564 void rfcomm_unregister_service(uint8_t service_channel){
2565     log_info("RFCOMM_UNREGISTER_SERVICE #%u", service_channel);
2566     rfcomm_service_t *service = rfcomm_service_for_channel(service_channel);
2567     if (!service) return;
2568     btstack_linked_list_remove(&rfcomm_services, (btstack_linked_item_t *) service);
2569     btstack_memory_rfcomm_service_free(service);
2570 
2571     // unregister if no services active
2572     if (btstack_linked_list_empty(&rfcomm_services)){
2573         // bt_send_cmd(&l2cap_unregister_service, BLUETOOTH_PROTOCOL_RFCOMM);
2574         l2cap_unregister_service(BLUETOOTH_PROTOCOL_RFCOMM);
2575     }
2576 }
2577 
2578 void rfcomm_accept_connection(uint16_t rfcomm_cid){
2579     log_info("RFCOMM_ACCEPT_CONNECTION cid 0x%02x", rfcomm_cid);
2580     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2581     if (!channel) return;
2582     switch (channel->state) {
2583         case RFCOMM_CHANNEL_INCOMING_SETUP:
2584             rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED);
2585             if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_PN){
2586                 rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP);
2587                 l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2588             }
2589             if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM){
2590                 rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_UA);
2591                 l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2592             }
2593             // at least one of { PN RSP, UA } needs to be sent
2594             // state transistion incoming setup -> dlc setup happens in rfcomm_run after these have been sent
2595             break;
2596         default:
2597             break;
2598     }
2599 
2600 }
2601 
2602 void rfcomm_decline_connection(uint16_t rfcomm_cid){
2603     log_info("RFCOMM_DECLINE_CONNECTION cid 0x%02x", rfcomm_cid);
2604     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2605     if (!channel) return;
2606     switch (channel->state) {
2607         case RFCOMM_CHANNEL_INCOMING_SETUP:
2608             channel->state = RFCOMM_CHANNEL_SEND_DM;
2609             l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2610             break;
2611         default:
2612             break;
2613     }
2614 }
2615 
2616 void rfcomm_grant_credits(uint16_t rfcomm_cid, uint8_t credits){
2617     log_info("RFCOMM_GRANT_CREDITS cid 0x%02x credits %u", rfcomm_cid, credits);
2618     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2619     if (!channel) return;
2620     if (!channel->incoming_flow_control) return;
2621     channel->new_credits_incoming += credits;
2622 
2623     // process
2624     l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2625 }
2626 
2627 #ifdef RFCOMM_USE_ERTM
2628 void rfcomm_enable_l2cap_ertm(void request_callback(rfcomm_ertm_request_t * request), void released_callback(uint16_t ertm_id)){
2629     rfcomm_ertm_request_callback  = request_callback;
2630     rfcomm_ertm_released_callback = released_callback;
2631 }
2632 #endif
2633