xref: /btstack/src/classic/rfcomm.c (revision 6420389d1a158883e8ea2b4bc8a58cdca363bf96)
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 <stdio.h>
45 #include <stdlib.h>
46 #include <string.h> // memcpy
47 #include <stdint.h>
48 
49 #include "bluetooth_sdp.h"
50 #include "btstack_debug.h"
51 #include "btstack_event.h"
52 #include "btstack_memory.h"
53 #include "btstack_util.h"
54 #include "classic/core.h"
55 #include "classic/rfcomm.h"
56 #include "hci.h"
57 #include "hci_cmd.h"
58 #include "hci_dump.h"
59 #include "l2cap.h"
60 
61 // workaround for missing PRIxPTR on mspgcc (16/20-bit MCU)
62 #ifndef PRIxPTR
63 #if defined(__MSP430X__)  &&  defined(__MSP430X_LARGE__)
64 #define PRIxPTR "lx"
65 #else
66 #define PRIxPTR "x"
67 #endif
68 #endif
69 
70 #define RFCOMM_MULIPLEXER_TIMEOUT_MS 60000
71 
72 #define RFCOMM_CREDITS 10
73 
74 // FCS calc
75 #define BT_RFCOMM_CODE_WORD         0xE0 // pol = x8+x2+x1+1
76 #define BT_RFCOMM_CRC_CHECK_LEN     3
77 #define BT_RFCOMM_UIHCRC_CHECK_LEN  2
78 
79 
80 typedef enum {
81     CH_EVT_RCVD_SABM = 1,
82     CH_EVT_RCVD_UA,
83     CH_EVT_RCVD_PN,
84     CH_EVT_RCVD_PN_RSP,
85     CH_EVT_RCVD_DISC,
86     CH_EVT_RCVD_DM,
87     CH_EVT_RCVD_MSC_CMD,
88     CH_EVT_RCVD_MSC_RSP,
89     CH_EVT_RCVD_NSC_RSP,
90     CH_EVT_RCVD_RLS_CMD,
91     CH_EVT_RCVD_RLS_RSP,
92     CH_EVT_RCVD_RPN_CMD,
93     CH_EVT_RCVD_RPN_REQ,
94     CH_EVT_RCVD_CREDITS,
95     CH_EVT_MULTIPLEXER_READY,
96     CH_EVT_READY_TO_SEND,
97 } RFCOMM_CHANNEL_EVENT;
98 
99 typedef struct rfcomm_channel_event {
100     RFCOMM_CHANNEL_EVENT type;
101     uint16_t dummy; // force rfcomm_channel_event to be 2-byte aligned -> avoid -Wcast-align warning
102 } rfcomm_channel_event_t;
103 
104 typedef struct rfcomm_channel_event_pn {
105     rfcomm_channel_event_t super;
106     uint16_t max_frame_size;
107     uint8_t  priority;
108     uint8_t  credits_outgoing;
109 } rfcomm_channel_event_pn_t;
110 
111 typedef struct rfcomm_channel_event_rpn {
112     rfcomm_channel_event_t super;
113     rfcomm_rpn_data_t data;
114 } rfcomm_channel_event_rpn_t;
115 
116 typedef struct rfcomm_channel_event_rls {
117     rfcomm_channel_event_t super;
118     uint8_t line_status;
119 } rfcomm_channel_event_rls_t;
120 
121 typedef struct rfcomm_channel_event_msc {
122     rfcomm_channel_event_t super;
123     uint8_t modem_status;
124 } rfcomm_channel_event_msc_t;
125 
126 
127 // global rfcomm data
128 static uint16_t      rfcomm_client_cid_generator;  // used for client channel IDs
129 
130 // linked lists for all
131 static btstack_linked_list_t rfcomm_multiplexers = NULL;
132 static btstack_linked_list_t rfcomm_channels = NULL;
133 static btstack_linked_list_t rfcomm_services = NULL;
134 
135 static gap_security_level_t rfcomm_security_level;
136 
137 static int  rfcomm_channel_can_send(rfcomm_channel_t * channel);
138 static int  rfcomm_channel_ready_for_open(rfcomm_channel_t *channel);
139 static int rfcomm_channel_ready_to_send(rfcomm_channel_t * channel);
140 static void rfcomm_channel_state_machine_with_channel(rfcomm_channel_t *channel, const rfcomm_channel_event_t *event, int * out_channel_valid);
141 static void rfcomm_channel_state_machine_with_dlci(rfcomm_multiplexer_t * multiplexer, uint8_t dlci, const rfcomm_channel_event_t *event);
142 static void rfcomm_emit_can_send_now(rfcomm_channel_t *channel);
143 static int rfcomm_multiplexer_ready_to_send(rfcomm_multiplexer_t * multiplexer);
144 static void rfcomm_multiplexer_state_machine(rfcomm_multiplexer_t * multiplexer, RFCOMM_MULTIPLEXER_EVENT event);
145 
146 // MARK: RFCOMM CLIENT EVENTS
147 
148 // data: event (8), len(8), address(48), channel (8), rfcomm_cid (16)
149 static void rfcomm_emit_connection_request(rfcomm_channel_t *channel) {
150     log_info("RFCOMM_EVENT_INCOMING_CONNECTION addr %s channel #%u cid 0x%02x",
151              bd_addr_to_str(channel->multiplexer->remote_addr), channel->dlci>>1, channel->rfcomm_cid);
152     uint8_t event[11];
153     event[0] = RFCOMM_EVENT_INCOMING_CONNECTION;
154     event[1] = sizeof(event) - 2;
155     reverse_bd_addr(channel->multiplexer->remote_addr, &event[2]);
156     event[8] = channel->dlci >> 1;
157     little_endian_store_16(event, 9, channel->rfcomm_cid);
158     hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
159 	(channel->packet_handler)(HCI_EVENT_PACKET, 0, event, sizeof(event));
160 }
161 
162 // API Change: BTstack-0.3.50x uses
163 // data: event(8), len(8), status (8), address (48), server channel(8), rfcomm_cid(16), max frame size(16)
164 // next Cydia release will use SVN version of this
165 // data: event(8), len(8), status (8), address (48), handle (16), server channel(8), rfcomm_cid(16), max frame size(16)
166 static void rfcomm_emit_channel_opened(rfcomm_channel_t *channel, uint8_t status) {
167     log_info("RFCOMM_EVENT_CHANNEL_OPENED status 0x%x addr %s handle 0x%x channel #%u cid 0x%02x mtu %u",
168              status, bd_addr_to_str(channel->multiplexer->remote_addr), channel->multiplexer->con_handle,
169              channel->dlci>>1, channel->rfcomm_cid, channel->max_frame_size);
170     uint8_t event[18];
171     uint8_t pos = 0;
172     event[pos++] = RFCOMM_EVENT_CHANNEL_OPENED;  // 0
173     event[pos++] = sizeof(event) - 2;                   // 1
174     event[pos++] = status;                              // 2
175     reverse_bd_addr(channel->multiplexer->remote_addr, &event[pos]); pos += 6; // 3
176     little_endian_store_16(event,  pos, channel->multiplexer->con_handle);   pos += 2; // 9
177 	event[pos++] = channel->dlci >> 1;                                      // 11
178 	little_endian_store_16(event, pos, channel->rfcomm_cid); pos += 2;                 // 12 - channel ID
179 	little_endian_store_16(event, pos, channel->max_frame_size); pos += 2;   // max frame size
180     event[pos++] = channel->service ? 1 : 0;    // linked to service -> incoming
181     hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
182 	(channel->packet_handler)(HCI_EVENT_PACKET, 0, event, pos);
183 
184     // if channel opened successfully, also send can send now if possible
185     if (status) return;
186     if (rfcomm_channel_can_send(channel)){
187         rfcomm_emit_can_send_now(channel);
188     }
189 }
190 
191 // data: event(8), len(8), rfcomm_cid(16)
192 static void rfcomm_emit_channel_closed(rfcomm_channel_t * channel) {
193     log_info("RFCOMM_EVENT_CHANNEL_CLOSED cid 0x%02x", channel->rfcomm_cid);
194     uint8_t event[4];
195     event[0] = RFCOMM_EVENT_CHANNEL_CLOSED;
196     event[1] = sizeof(event) - 2;
197     little_endian_store_16(event, 2, channel->rfcomm_cid);
198     hci_dump_packet(HCI_EVENT_PACKET, 0, event, sizeof(event));
199 	(channel->packet_handler)(HCI_EVENT_PACKET, 0, event, sizeof(event));
200 }
201 
202 static void rfcomm_emit_remote_line_status(rfcomm_channel_t *channel, uint8_t line_status){
203     log_info("RFCOMM_EVENT_REMOTE_LINE_STATUS cid 0x%02x c, line status 0x%x", channel->rfcomm_cid, line_status);
204     uint8_t event[5];
205     event[0] = RFCOMM_EVENT_REMOTE_LINE_STATUS;
206     event[1] = sizeof(event) - 2;
207     little_endian_store_16(event, 2, channel->rfcomm_cid);
208     event[4] = line_status;
209     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
210     (channel->packet_handler)(HCI_EVENT_PACKET, 0, event, sizeof(event));
211 }
212 
213 static void rfcomm_emit_port_configuration(rfcomm_channel_t *channel){
214     // notify client about new settings
215     uint8_t event[2+sizeof(rfcomm_rpn_data_t)];
216     event[0] = RFCOMM_EVENT_PORT_CONFIGURATION;
217     event[1] = sizeof(rfcomm_rpn_data_t);
218     memcpy(&event[2], (uint8_t*) &channel->rpn_data, sizeof(rfcomm_rpn_data_t));
219     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
220     (channel->packet_handler)(HCI_EVENT_PACKET, channel->rfcomm_cid, event, sizeof(event));
221 }
222 
223 static void rfcomm_emit_can_send_now(rfcomm_channel_t *channel) {
224     log_debug("RFCOMM_EVENT_CHANNEL_CAN_SEND_NOW local_cid 0x%x", channel->rfcomm_cid);
225     uint8_t event[4];
226     event[0] = RFCOMM_EVENT_CAN_SEND_NOW;
227     event[1] = sizeof(event) - 2;
228     little_endian_store_16(event, 2, channel->rfcomm_cid);
229     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
230     (channel->packet_handler)(HCI_EVENT_PACKET, channel->rfcomm_cid, event, sizeof(event));
231 }
232 
233 // MARK RFCOMM RPN DATA HELPER
234 static void rfcomm_rpn_data_set_defaults(rfcomm_rpn_data_t * rpn_data){
235         rpn_data->baud_rate = RPN_BAUD_9600;  /* 9600 bps */
236         rpn_data->flags = 0x03;               /* 8-n-1 */
237         rpn_data->flow_control = 0;           /* no flow control */
238         rpn_data->xon  = 0xd1;                /* XON */
239         rpn_data->xoff = 0xd3;                /* XOFF */
240         rpn_data->parameter_mask_0 = 0x7f;    /* parameter mask, all values set */
241         rpn_data->parameter_mask_1 = 0x3f;    /* parameter mask, all values set */
242 }
243 
244 static void rfcomm_rpn_data_update(rfcomm_rpn_data_t * dest, rfcomm_rpn_data_t * src){
245     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_BAUD){
246         dest->baud_rate = src->baud_rate;
247     }
248     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_DATA_BITS){
249         dest->flags = (dest->flags & 0xfc) | (src->flags & 0x03);
250     }
251     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_STOP_BITS){
252         dest->flags = (dest->flags & 0xfb) | (src->flags & 0x04);
253     }
254     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_PARITY){
255         dest->flags = (dest->flags & 0xf7) | (src->flags & 0x08);
256     }
257     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_PARITY_TYPE){
258         dest->flags = (dest->flags & 0xfc) | (src->flags & 0x30);
259     }
260     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_XON_CHAR){
261         dest->xon = src->xon;
262     }
263     if (src->parameter_mask_0 & RPN_PARAM_MASK_0_XOFF_CHAR){
264         dest->xoff = src->xoff;
265     }
266     int i;
267     for (i=0; i < 6 ; i++){
268         uint8_t mask = 1 << i;
269         if (src->parameter_mask_1 & mask){
270             dest->flags = (dest->flags & ~mask) | (src->flags & mask);
271         }
272     }
273     // always copy parameter mask, too. informative for client, needed for response
274     dest->parameter_mask_0 = src->parameter_mask_0;
275     dest->parameter_mask_1 = src->parameter_mask_1;
276 }
277 // MARK: RFCOMM MULTIPLEXER HELPER
278 
279 static uint16_t rfcomm_max_frame_size_for_l2cap_mtu(uint16_t l2cap_mtu){
280     // Assume RFCOMM header without credits and 2 byte (14 bit) length field
281     uint16_t max_frame_size = l2cap_mtu - 5;
282     log_info("rfcomm_max_frame_size_for_l2cap_mtu:  %u -> %u", l2cap_mtu, max_frame_size);
283     return max_frame_size;
284 }
285 
286 static void rfcomm_multiplexer_initialize(rfcomm_multiplexer_t *multiplexer){
287 
288     memset(multiplexer, 0, sizeof(rfcomm_multiplexer_t));
289 
290     multiplexer->state = RFCOMM_MULTIPLEXER_CLOSED;
291     multiplexer->fcon = 1;
292     multiplexer->send_dm_for_dlci = 0;
293     multiplexer->max_frame_size = rfcomm_max_frame_size_for_l2cap_mtu(l2cap_max_mtu());
294     multiplexer->test_data_len = 0;
295     multiplexer->nsc_command = 0;
296 }
297 
298 static rfcomm_multiplexer_t * rfcomm_multiplexer_create_for_addr(bd_addr_t addr){
299 
300     // alloc structure
301     rfcomm_multiplexer_t * multiplexer = btstack_memory_rfcomm_multiplexer_get();
302     if (!multiplexer) return NULL;
303 
304     // fill in
305     rfcomm_multiplexer_initialize(multiplexer);
306     bd_addr_copy(multiplexer->remote_addr, addr);
307 
308     // add to services list
309     btstack_linked_list_add(&rfcomm_multiplexers, (btstack_linked_item_t *) multiplexer);
310 
311     return multiplexer;
312 }
313 
314 static rfcomm_multiplexer_t * rfcomm_multiplexer_for_addr(bd_addr_t addr){
315     btstack_linked_item_t *it;
316     for (it = (btstack_linked_item_t *) rfcomm_multiplexers; it ; it = it->next){
317         rfcomm_multiplexer_t * multiplexer = ((rfcomm_multiplexer_t *) it);
318         // ignore multiplexer in shutdown
319         if (multiplexer->state == RFCOMM_MULTIPLEXER_SHUTTING_DOWN) continue;
320         if (bd_addr_cmp(addr, multiplexer->remote_addr) == 0) {
321             return multiplexer;
322         };
323     }
324     return NULL;
325 }
326 
327 static rfcomm_multiplexer_t * rfcomm_multiplexer_for_l2cap_cid(uint16_t l2cap_cid) {
328     btstack_linked_item_t *it;
329     for (it = (btstack_linked_item_t *) rfcomm_multiplexers; it ; it = it->next){
330         rfcomm_multiplexer_t * multiplexer = ((rfcomm_multiplexer_t *) it);
331         if (multiplexer->l2cap_cid == l2cap_cid) {
332             return multiplexer;
333         };
334     }
335     return NULL;
336 }
337 
338 static int rfcomm_multiplexer_has_channels(rfcomm_multiplexer_t * multiplexer){
339     btstack_linked_item_t *it;
340     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
341         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
342         if (channel->multiplexer == multiplexer) {
343             return 1;
344         }
345     }
346     return 0;
347 }
348 
349 // MARK: RFCOMM CHANNEL HELPER
350 
351 static void rfcomm_dump_channels(void){
352     btstack_linked_item_t * it;
353     int channels = 0;
354     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
355         rfcomm_channel_t * channel = (rfcomm_channel_t *) it;
356         log_info("Channel #%u: addr %p, state %u", channels, channel, channel->state);
357         channels++;
358     }
359 }
360 
361 static void rfcomm_channel_initialize(rfcomm_channel_t *channel, rfcomm_multiplexer_t *multiplexer,
362                                rfcomm_service_t *service, uint8_t server_channel){
363 
364     // don't use 0 as channel id
365     if (rfcomm_client_cid_generator == 0) ++rfcomm_client_cid_generator;
366 
367     // setup channel
368     memset(channel, 0, sizeof(rfcomm_channel_t));
369 
370     // set defaults for port configuration (even for services)
371     rfcomm_rpn_data_set_defaults(&channel->rpn_data);
372 
373     channel->state            = RFCOMM_CHANNEL_CLOSED;
374     channel->state_var        = RFCOMM_CHANNEL_STATE_VAR_NONE;
375 
376     channel->multiplexer      = multiplexer;
377     channel->rfcomm_cid       = rfcomm_client_cid_generator++;
378     channel->max_frame_size   = multiplexer->max_frame_size;
379 
380     channel->credits_incoming = 0;
381     channel->credits_outgoing = 0;
382 
383     // incoming flow control not active
384     channel->new_credits_incoming  = RFCOMM_CREDITS;
385     channel->incoming_flow_control = 0;
386 
387     channel->rls_line_status       = RFCOMM_RLS_STATUS_INVALID;
388 
389     channel->service = service;
390 	if (service) {
391 		// incoming connection
392     	channel->dlci = (server_channel << 1) |  multiplexer->outgoing;
393         if (channel->max_frame_size > service->max_frame_size) {
394             channel->max_frame_size = service->max_frame_size;
395         }
396         channel->incoming_flow_control = service->incoming_flow_control;
397         channel->new_credits_incoming  = service->incoming_initial_credits;
398         channel->packet_handler        = service->packet_handler;
399 	} else {
400 		// outgoing connection
401 		channel->dlci = (server_channel << 1) | (multiplexer->outgoing ^ 1);
402 	}
403 }
404 
405 // service == NULL -> outgoing channel
406 static rfcomm_channel_t * rfcomm_channel_create(rfcomm_multiplexer_t * multiplexer,
407                                                 rfcomm_service_t * service, uint8_t server_channel){
408 
409     log_info("rfcomm_channel_create for service %p, channel %u --- list of channels:", service, server_channel);
410     rfcomm_dump_channels();
411 
412     // alloc structure
413     rfcomm_channel_t * channel = btstack_memory_rfcomm_channel_get();
414     if (!channel) return NULL;
415 
416     // fill in
417     rfcomm_channel_initialize(channel, multiplexer, service, server_channel);
418 
419     // add to services list
420     btstack_linked_list_add(&rfcomm_channels, (btstack_linked_item_t *) channel);
421 
422     return channel;
423 }
424 
425 static void rfcomm_notify_channel_can_send(void){
426     btstack_linked_list_iterator_t it;
427     btstack_linked_list_iterator_init(&it, &rfcomm_channels);
428     while (btstack_linked_list_iterator_has_next(&it)){
429         rfcomm_channel_t * channel = (rfcomm_channel_t *) btstack_linked_list_iterator_next(&it);
430         if (!channel->waiting_for_can_send_now) continue; // didn't try to send yet
431         if (!rfcomm_channel_can_send(channel)) continue;  // or cannot yet either
432 
433         channel->waiting_for_can_send_now = 0;
434         rfcomm_emit_can_send_now(channel);
435     }
436 }
437 
438 static rfcomm_channel_t * rfcomm_channel_for_rfcomm_cid(uint16_t rfcomm_cid){
439     btstack_linked_item_t *it;
440     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
441         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
442         if (channel->rfcomm_cid == rfcomm_cid) {
443             return channel;
444         };
445     }
446     return NULL;
447 }
448 
449 static rfcomm_channel_t * rfcomm_channel_for_multiplexer_and_dlci(rfcomm_multiplexer_t * multiplexer, uint8_t dlci){
450     btstack_linked_item_t *it;
451     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
452         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
453         if (channel->dlci == dlci && channel->multiplexer == multiplexer) {
454             return channel;
455         };
456     }
457     return NULL;
458 }
459 
460 static rfcomm_service_t * rfcomm_service_for_channel(uint8_t server_channel){
461     btstack_linked_item_t *it;
462     for (it = (btstack_linked_item_t *) rfcomm_services; it ; it = it->next){
463         rfcomm_service_t * service = ((rfcomm_service_t *) it);
464         if ( service->server_channel == server_channel){
465             return service;
466         };
467     }
468     return NULL;
469 }
470 
471 // MARK: RFCOMM SEND
472 
473 /**
474  * @param credits - only used for RFCOMM flow control in UIH wiht P/F = 1
475  */
476 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){
477 
478     if (!l2cap_can_send_packet_now(multiplexer->l2cap_cid)) return BTSTACK_ACL_BUFFERS_FULL;
479 
480     l2cap_reserve_packet_buffer();
481     uint8_t * rfcomm_out_buffer = l2cap_get_outgoing_buffer();
482 
483 	uint16_t pos = 0;
484 	uint8_t crc_fields = 3;
485 
486 	rfcomm_out_buffer[pos++] = address;
487 	rfcomm_out_buffer[pos++] = control;
488 
489 	// length field can be 1 or 2 octets
490 	if (len < 128){
491 		rfcomm_out_buffer[pos++] = (len << 1)| 1;     // bits 0-6
492 	} else {
493 		rfcomm_out_buffer[pos++] = (len & 0x7f) << 1; // bits 0-6
494 		rfcomm_out_buffer[pos++] = len >> 7;          // bits 7-14
495 		crc_fields++;
496 	}
497 
498 	// add credits for UIH frames when PF bit is set
499 	if (control == BT_RFCOMM_UIH_PF){
500 		rfcomm_out_buffer[pos++] = credits;
501 	}
502 
503 	// copy actual data
504 	if (len) {
505 		memcpy(&rfcomm_out_buffer[pos], data, len);
506 		pos += len;
507 	}
508 
509 	// UIH frames only calc FCS over address + control (5.1.1)
510 	if ((control & 0xef) == BT_RFCOMM_UIH){
511 		crc_fields = 2;
512 	}
513 	rfcomm_out_buffer[pos++] =  btstack_crc8_calc(rfcomm_out_buffer, crc_fields); // calc fcs
514 
515     int err = l2cap_send_prepared(multiplexer->l2cap_cid, pos);
516 
517     return err;
518 }
519 
520 // simplified version of rfcomm_send_packet_for_multiplexer for prepared rfcomm packet (UIH, 2 byte len, no credits)
521 static int rfcomm_send_uih_prepared(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint16_t len){
522 
523     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) | (dlci << 2);
524     uint8_t control = BT_RFCOMM_UIH;
525 
526     uint8_t * rfcomm_out_buffer = l2cap_get_outgoing_buffer();
527 
528     uint16_t pos = 0;
529     rfcomm_out_buffer[pos++] = address;
530     rfcomm_out_buffer[pos++] = control;
531     rfcomm_out_buffer[pos++] = (len & 0x7f) << 1; // bits 0-6
532     rfcomm_out_buffer[pos++] = len >> 7;          // bits 7-14
533 
534     // actual data is already in place
535     pos += len;
536 
537     // UIH frames only calc FCS over address + control (5.1.1)
538     rfcomm_out_buffer[pos++] =  btstack_crc8_calc(rfcomm_out_buffer, 2); // calc fcs
539 
540     int err = l2cap_send_prepared(multiplexer->l2cap_cid, pos);
541 
542     return err;
543 }
544 
545 // C/R Flag in Address
546 // - terms: initiator = station that creates multiplexer with SABM
547 // - terms: responder = station that responds to multiplexer setup with UA
548 // "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"
549 //    - command initiator = 1 /response responder = 1
550 //    - command responder = 0 /response initiator = 0
551 // "For UIH frames, the C/R bit is always set according to section 5.4.3.1 in GSM 07.10.
552 //  This applies independently of what is contained wthin the UIH frames, either data or control messages."
553 //    - c/r = 1 for frames by initiating station, 0 = for frames by responding station
554 
555 // C/R Flag in Message
556 // "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."
557 //   - If the C/R bit is set to 1 the message is a command
558 //   - if it is set to 0 the message is a response.
559 
560 // temp/old messge construction
561 
562 // new object oriented version
563 static int rfcomm_send_sabm(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
564 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) | (dlci << 2);   // command
565     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_SABM, 0, NULL, 0);
566 }
567 
568 static int rfcomm_send_disc(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
569 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) | (dlci << 2);  // command
570     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_DISC, 0, NULL, 0);
571 }
572 
573 static int rfcomm_send_ua(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
574 	uint8_t address = (1 << 0) | ((multiplexer->outgoing ^ 1) << 1) | (dlci << 2); // response
575     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UA, 0, NULL, 0);
576 }
577 
578 static int rfcomm_send_dm_pf(rfcomm_multiplexer_t *multiplexer, uint8_t dlci){
579 	uint8_t address = (1 << 0) | ((multiplexer->outgoing ^ 1) << 1) | (dlci << 2); // response
580     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_DM_PF, 0, NULL, 0);
581 }
582 
583 static int rfcomm_send_uih_fc_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t fcon) {
584     uint8_t address = (1 << 0) | (multiplexer->outgoing<< 1);
585     uint8_t payload[2];
586     uint8_t pos = 0;
587     payload[pos++] = fcon ? BT_RFCOMM_FCON_RSP : BT_RFCOMM_FCOFF_RSP;
588     payload[pos++] = (0 << 1) | 1;  // len
589     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
590 }
591 
592 // static int rfcomm_send_uih_test_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t * data, uint16_t len) {
593 //     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
594 //     uint8_t payload[2+len];
595 //     uint8_t pos = 0;
596 //     payload[pos++] = BT_RFCOMM_TEST_CMD;
597 //     payload[pos++] = (len + 1) << 1 | 1;  // len
598 //     memcpy(&payload[pos], data, len);
599 //     pos += len;
600 //     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
601 // }
602 
603 static int rfcomm_send_uih_test_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t * data, uint16_t len) {
604     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
605     uint8_t payload[2+RFCOMM_TEST_DATA_MAX_LEN];
606     uint8_t pos = 0;
607     payload[pos++] = BT_RFCOMM_TEST_RSP;
608     if (len > RFCOMM_TEST_DATA_MAX_LEN) {
609         len = RFCOMM_TEST_DATA_MAX_LEN;
610     }
611     payload[pos++] = (len << 1) | 1;  // len
612     memcpy(&payload[pos], data, len);
613     pos += len;
614     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
615 }
616 
617 static int rfcomm_send_uih_msc_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t signals) {
618 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
619 	uint8_t payload[4];
620 	uint8_t pos = 0;
621 	payload[pos++] = BT_RFCOMM_MSC_CMD;
622 	payload[pos++] = (2 << 1) | 1;  // len
623 	payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
624 	payload[pos++] = signals;
625 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
626 }
627 
628 static int rfcomm_send_uih_msc_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t signals) {
629 	uint8_t address = (1 << 0) | (multiplexer->outgoing<< 1);
630 	uint8_t payload[4];
631 	uint8_t pos = 0;
632 	payload[pos++] = BT_RFCOMM_MSC_RSP;
633 	payload[pos++] = (2 << 1) | 1;  // len
634 	payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
635 	payload[pos++] = signals;
636 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
637 }
638 
639 static int rfcomm_send_uih_nsc_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t command) {
640     uint8_t address = (1 << 0) | (multiplexer->outgoing<< 1);
641     uint8_t payload[3];
642     uint8_t pos = 0;
643     payload[pos++] = BT_RFCOMM_NSC_RSP;
644     payload[pos++] = (1 << 1) | 1;  // len
645     payload[pos++] = command;
646     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
647 }
648 
649 static int rfcomm_send_uih_pn_command(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint16_t max_frame_size){
650 	uint8_t payload[10];
651 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
652 	uint8_t pos = 0;
653 	payload[pos++] = BT_RFCOMM_PN_CMD;
654 	payload[pos++] = (8 << 1) | 1;  // len
655 	payload[pos++] = dlci;
656 	payload[pos++] = 0xf0; // pre-defined for Bluetooth, see 5.5.3 of TS 07.10 Adaption for RFCOMM
657 	payload[pos++] = 0; // priority
658 	payload[pos++] = 0; // max 60 seconds ack
659 	payload[pos++] = max_frame_size & 0xff; // max framesize low
660 	payload[pos++] = max_frame_size >> 8;   // max framesize high
661 	payload[pos++] = 0x00; // number of retransmissions
662 	payload[pos++] = 0x00; // (unused error recovery window) initial number of credits
663 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
664 }
665 
666 // "The response may not change the DLCI, the priority, the convergence layer, or the timer value." rfcomm_tutorial.pdf
667 static int rfcomm_send_uih_pn_response(rfcomm_multiplexer_t *multiplexer, uint8_t dlci,
668                                        uint8_t priority, uint16_t max_frame_size){
669 	uint8_t payload[10];
670 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
671 	uint8_t pos = 0;
672 	payload[pos++] = BT_RFCOMM_PN_RSP;
673 	payload[pos++] = (8 << 1) | 1;  // len
674 	payload[pos++] = dlci;
675 	payload[pos++] = 0xe0; // pre defined for Bluetooth, see 5.5.3 of TS 07.10 Adaption for RFCOMM
676 	payload[pos++] = priority; // priority
677 	payload[pos++] = 0; // max 60 seconds ack
678 	payload[pos++] = max_frame_size & 0xff; // max framesize low
679 	payload[pos++] = max_frame_size >> 8;   // max framesize high
680 	payload[pos++] = 0x00; // number of retransmissions
681 	payload[pos++] = 0x00; // (unused error recovery window) initial number of credits
682 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
683 }
684 
685 static int rfcomm_send_uih_rls_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t line_status) {
686     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
687     uint8_t payload[4];
688     uint8_t pos = 0;
689     payload[pos++] = BT_RFCOMM_RLS_CMD;
690     payload[pos++] = (2 << 1) | 1;  // len
691     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
692     payload[pos++] = line_status;
693     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
694 }
695 
696 static int rfcomm_send_uih_rls_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, uint8_t line_status) {
697     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
698     uint8_t payload[4];
699     uint8_t pos = 0;
700     payload[pos++] = BT_RFCOMM_RLS_RSP;
701     payload[pos++] = (2 << 1) | 1;  // len
702     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
703     payload[pos++] = line_status;
704     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
705 }
706 
707 static int rfcomm_send_uih_rpn_cmd(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, rfcomm_rpn_data_t *rpn_data) {
708     uint8_t payload[10];
709     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
710     uint8_t pos = 0;
711     payload[pos++] = BT_RFCOMM_RPN_CMD;
712     payload[pos++] = (8 << 1) | 1;  // len
713     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
714     payload[pos++] = rpn_data->baud_rate;
715     payload[pos++] = rpn_data->flags;
716     payload[pos++] = rpn_data->flow_control;
717     payload[pos++] = rpn_data->xon;
718     payload[pos++] = rpn_data->xoff;
719     payload[pos++] = rpn_data->parameter_mask_0;
720     payload[pos++] = rpn_data->parameter_mask_1;
721     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
722 }
723 
724 static int rfcomm_send_uih_rpn_req(rfcomm_multiplexer_t *multiplexer, uint8_t dlci) {
725     uint8_t payload[3];
726     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
727     uint8_t pos = 0;
728     payload[pos++] = BT_RFCOMM_RPN_CMD;
729     payload[pos++] = (1 << 1) | 1;  // len
730     payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
731     return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
732 }
733 
734 static int rfcomm_send_uih_rpn_rsp(rfcomm_multiplexer_t *multiplexer, uint8_t dlci, rfcomm_rpn_data_t *rpn_data) {
735 	uint8_t payload[10];
736 	uint8_t address = (1 << 0) | (multiplexer->outgoing << 1);
737 	uint8_t pos = 0;
738 	payload[pos++] = BT_RFCOMM_RPN_RSP;
739 	payload[pos++] = (8 << 1) | 1;  // len
740 	payload[pos++] = (1 << 0) | (1 << 1) | (dlci << 2); // CMD => C/R = 1
741 	payload[pos++] = rpn_data->baud_rate;
742 	payload[pos++] = rpn_data->flags;
743 	payload[pos++] = rpn_data->flow_control;
744 	payload[pos++] = rpn_data->xon;
745 	payload[pos++] = rpn_data->xoff;
746 	payload[pos++] = rpn_data->parameter_mask_0;
747 	payload[pos++] = rpn_data->parameter_mask_1;
748 	return rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH, 0, (uint8_t *) payload, pos);
749 }
750 
751 static void rfcomm_send_uih_credits(rfcomm_multiplexer_t *multiplexer, uint8_t dlci,  uint8_t credits){
752     uint8_t address = (1 << 0) | (multiplexer->outgoing << 1) |  (dlci << 2);
753     rfcomm_send_packet_for_multiplexer(multiplexer, address, BT_RFCOMM_UIH_PF, credits, NULL, 0);
754 }
755 
756 // MARK: RFCOMM MULTIPLEXER
757 static void rfcomm_multiplexer_stop_timer(rfcomm_multiplexer_t * multiplexer){
758     if (multiplexer->timer_active) {
759         btstack_run_loop_remove_timer(&multiplexer->timer);
760         multiplexer->timer_active = 0;
761     }
762 }
763 static void rfcomm_multiplexer_free(rfcomm_multiplexer_t * multiplexer){
764     btstack_linked_list_remove( &rfcomm_multiplexers, (btstack_linked_item_t *) multiplexer);
765     btstack_memory_rfcomm_multiplexer_free(multiplexer);
766 }
767 
768 static void rfcomm_multiplexer_finalize(rfcomm_multiplexer_t * multiplexer){
769     // remove (potential) timer
770     rfcomm_multiplexer_stop_timer(multiplexer);
771 
772     // close and remove all channels
773     btstack_linked_item_t *it = (btstack_linked_item_t *) &rfcomm_channels;
774     while (it->next){
775         rfcomm_channel_t * channel = (rfcomm_channel_t *) it->next;
776         if (channel->multiplexer == multiplexer) {
777             // emit appropriate events
778             switch(channel->state){
779                 case RFCOMM_CHANNEL_OPEN:
780                 case RFCOMM_CHANNEL_W4_UA_AFTER_DISC:
781                     rfcomm_emit_channel_closed(channel);
782                     break;
783                 case RFCOMM_CHANNEL_SEND_UA_AFTER_DISC:
784                     // remote didn't wait until we send the UA disc
785                     break;
786                 default:
787                     rfcomm_emit_channel_opened(channel, RFCOMM_MULTIPLEXER_STOPPED);
788                     break;
789             }
790             // remove from list
791             it->next = it->next->next;
792             // free channel struct
793             btstack_memory_rfcomm_channel_free(channel);
794         } else {
795             it = it->next;
796         }
797     }
798 
799     // remove mutliplexer
800     rfcomm_multiplexer_free(multiplexer);
801 }
802 
803 static void rfcomm_multiplexer_timer_handler(btstack_timer_source_t *timer){
804     rfcomm_multiplexer_t * multiplexer = (rfcomm_multiplexer_t*) btstack_run_loop_get_timer_context(timer);
805     if (rfcomm_multiplexer_has_channels(multiplexer)) return;
806 
807     log_info("rfcomm_multiplexer_timer_handler timeout: shutting down multiplexer! (no channels)");
808     uint16_t l2cap_cid = multiplexer->l2cap_cid;
809     rfcomm_multiplexer_finalize(multiplexer);
810     l2cap_disconnect(l2cap_cid, 0x13);
811 }
812 
813 static void rfcomm_multiplexer_prepare_idle_timer(rfcomm_multiplexer_t * multiplexer){
814     if (multiplexer->timer_active) {
815         btstack_run_loop_remove_timer(&multiplexer->timer);
816         multiplexer->timer_active = 0;
817     }
818     if (rfcomm_multiplexer_has_channels(multiplexer)) return;
819 
820     // start idle timer for multiplexer timeout check as there are no rfcomm channels yet
821     btstack_run_loop_set_timer(&multiplexer->timer, RFCOMM_MULIPLEXER_TIMEOUT_MS);
822     btstack_run_loop_set_timer_handler(&multiplexer->timer, rfcomm_multiplexer_timer_handler);
823     btstack_run_loop_set_timer_context(&multiplexer->timer, multiplexer);
824     btstack_run_loop_add_timer(&multiplexer->timer);
825     multiplexer->timer_active = 1;
826 }
827 
828 static void rfcomm_multiplexer_opened(rfcomm_multiplexer_t *multiplexer){
829     log_info("Multiplexer up and running");
830     multiplexer->state = RFCOMM_MULTIPLEXER_OPEN;
831 
832     const rfcomm_channel_event_t event = { CH_EVT_MULTIPLEXER_READY, 0};
833 
834     // transition of channels that wait for multiplexer
835     btstack_linked_item_t *it;
836     for (it = (btstack_linked_item_t *) rfcomm_channels; it ; it = it->next){
837         rfcomm_channel_t * channel = ((rfcomm_channel_t *) it);
838         if (channel->multiplexer != multiplexer) continue;
839         int rfcomm_channel_valid = 1;
840         rfcomm_channel_state_machine_with_channel(channel, &event, &rfcomm_channel_valid);
841         if (rfcomm_channel_valid && rfcomm_channel_ready_to_send(channel)){
842             l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
843         }
844     }
845     rfcomm_multiplexer_prepare_idle_timer(multiplexer);
846 
847     // request can send now for multiplexer if ready
848     if (rfcomm_multiplexer_ready_to_send(multiplexer)){
849         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
850     }
851 }
852 
853 static void rfcomm_handle_can_send_now(uint16_t l2cap_cid){
854 
855     log_debug("rfcomm_handle_can_send_now enter: %u", l2cap_cid);
856 
857     btstack_linked_list_iterator_t it;
858     int token_consumed = 0;
859 
860     // forward token to multiplexer
861     btstack_linked_list_iterator_init(&it, &rfcomm_multiplexers);
862     while (!token_consumed && btstack_linked_list_iterator_has_next(&it)){
863         rfcomm_multiplexer_t * multiplexer = (rfcomm_multiplexer_t *) btstack_linked_list_iterator_next(&it);
864         if (multiplexer->l2cap_cid != l2cap_cid) continue;
865         if (rfcomm_multiplexer_ready_to_send(multiplexer)){
866             log_debug("rfcomm_handle_can_send_now enter: multiplexer token");
867             token_consumed = 1;
868             rfcomm_multiplexer_state_machine(multiplexer, MULT_EV_READY_TO_SEND);
869         }
870     }
871 
872     // forward token to channel state machine
873     btstack_linked_list_iterator_init(&it, &rfcomm_channels);
874     while (!token_consumed && btstack_linked_list_iterator_has_next(&it)){
875         rfcomm_channel_t * channel = (rfcomm_channel_t *) btstack_linked_list_iterator_next(&it);
876         if (channel->multiplexer->l2cap_cid != l2cap_cid) continue;
877         // channel state machine
878         if (rfcomm_channel_ready_to_send(channel)){
879             log_debug("rfcomm_handle_can_send_now enter: channel token");
880             token_consumed = 1;
881             const rfcomm_channel_event_t event = { CH_EVT_READY_TO_SEND, 0 };
882             int rfcomm_channel_valid = 1;
883             rfcomm_channel_state_machine_with_channel(channel, &event, &rfcomm_channel_valid);
884         }
885     }
886 
887     // forward token to client
888     btstack_linked_list_iterator_init(&it, &rfcomm_channels);
889     while (!token_consumed && btstack_linked_list_iterator_has_next(&it)){
890         rfcomm_channel_t * channel = (rfcomm_channel_t *) btstack_linked_list_iterator_next(&it);
891         if (channel->multiplexer->l2cap_cid != l2cap_cid) continue;
892         // client waiting for can send now
893         if (!channel->waiting_for_can_send_now)    continue;
894         if ((channel->multiplexer->fcon & 1) == 0) continue;
895         if (!channel->credits_outgoing){
896             log_debug("rfcomm_handle_can_send_now waiting to send but no credits (ignore)");
897             continue;
898         }
899 
900         log_debug("rfcomm_handle_can_send_now enter: client token");
901         token_consumed = 1;
902         channel->waiting_for_can_send_now = 0;
903         rfcomm_emit_can_send_now(channel);
904     }
905 
906     // if token was consumed, request another one
907     if (token_consumed) {
908         l2cap_request_can_send_now_event(l2cap_cid);
909     }
910 
911     log_debug("rfcomm_handle_can_send_now exit");
912 }
913 
914 static void rfcomm_multiplexer_set_state_and_request_can_send_now_event(rfcomm_multiplexer_t * multiplexer, RFCOMM_MULTIPLEXER_STATE state){
915     multiplexer->state = state;
916     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
917 }
918 
919 /**
920  * @return handled packet
921  */
922 static int rfcomm_hci_event_handler(uint8_t *packet, uint16_t size){
923 
924     UNUSED(size);   // ok: handling own l2cap events
925 
926     bd_addr_t event_addr;
927     uint16_t  psm;
928     uint16_t l2cap_cid;
929     hci_con_handle_t con_handle;
930     rfcomm_multiplexer_t *multiplexer = NULL;
931     uint8_t status;
932 
933     switch (hci_event_packet_get_type(packet)) {
934 
935         // accept incoming rfcomm connection if no multiplexer exists yet
936         case L2CAP_EVENT_INCOMING_CONNECTION:
937             // data: event(8), len(8), address(48), handle (16),  psm (16), source cid(16) dest cid(16)
938             reverse_bd_addr(&packet[2], event_addr);
939             con_handle = little_endian_read_16(packet,  8);
940             psm        = little_endian_read_16(packet, 10);
941             l2cap_cid  = little_endian_read_16(packet, 12);
942 
943             if (psm != BLUETOOTH_PROTOCOL_RFCOMM) break;
944 
945             multiplexer = rfcomm_multiplexer_for_addr(event_addr);
946 
947             if (multiplexer) {
948                 log_info("INCOMING_CONNECTION (l2cap_cid 0x%02x) for BLUETOOTH_PROTOCOL_RFCOMM => decline - multiplexer already exists", l2cap_cid);
949                 l2cap_decline_connection(l2cap_cid);
950                 return 1;
951             }
952 
953             // create and inititialize new multiplexer instance (incoming)
954             multiplexer = rfcomm_multiplexer_create_for_addr(event_addr);
955             if (!multiplexer){
956                 log_info("INCOMING_CONNECTION (l2cap_cid 0x%02x) for BLUETOOTH_PROTOCOL_RFCOMM => decline - no memory left", l2cap_cid);
957                 l2cap_decline_connection(l2cap_cid);
958                 return 1;
959             }
960 
961             multiplexer->con_handle = con_handle;
962             multiplexer->l2cap_cid = l2cap_cid;
963             //
964             multiplexer->state = RFCOMM_MULTIPLEXER_W4_SABM_0;
965             log_info("L2CAP_EVENT_INCOMING_CONNECTION (l2cap_cid 0x%02x) for BLUETOOTH_PROTOCOL_RFCOMM => accept", l2cap_cid);
966             l2cap_accept_connection(l2cap_cid);
967             return 1;
968 
969         // l2cap connection opened -> store l2cap_cid, remote_addr
970         case L2CAP_EVENT_CHANNEL_OPENED:
971 
972             if (little_endian_read_16(packet, 11) != BLUETOOTH_PROTOCOL_RFCOMM) break;
973 
974             status = packet[2];
975             log_info("L2CAP_EVENT_CHANNEL_OPENED for BLUETOOTH_PROTOCOL_RFCOMM, status %u", status);
976 
977             // get multiplexer for remote addr
978             con_handle = little_endian_read_16(packet, 9);
979             l2cap_cid = little_endian_read_16(packet, 13);
980             reverse_bd_addr(&packet[3], event_addr);
981             multiplexer = rfcomm_multiplexer_for_addr(event_addr);
982             if (!multiplexer) {
983                 log_error("L2CAP_EVENT_CHANNEL_OPENED but no multiplexer prepared");
984                 return 1;
985             }
986 
987             // on l2cap open error discard everything
988             if (status){
989 
990                 // remove (potential) timer
991                 rfcomm_multiplexer_stop_timer(multiplexer);
992 
993                 // mark multiplexer as shutting down
994                 multiplexer->state = RFCOMM_MULTIPLEXER_SHUTTING_DOWN;
995 
996                 // emit rfcomm_channel_opened with status and free channel
997                 // note: repeatedly go over list until full iteration causes no further change
998                 int done;
999                 do {
1000                     done = 1;
1001                     btstack_linked_item_t * it = (btstack_linked_item_t *) &rfcomm_channels;
1002                     while (it->next) {
1003                         rfcomm_channel_t * channel = (rfcomm_channel_t *) it->next;
1004                         if (channel->multiplexer == multiplexer){
1005                             done = 0;
1006                             rfcomm_emit_channel_opened(channel, status);
1007                             btstack_linked_list_remove(&rfcomm_channels, (btstack_linked_item_t *) channel);
1008                             btstack_memory_rfcomm_channel_free(channel);
1009                             break;
1010                         } else {
1011                             it = it->next;
1012                         }
1013                     }
1014                 } while (!done);
1015 
1016                 // free multiplexer
1017                 rfcomm_multiplexer_free(multiplexer);
1018                 return 1;
1019             }
1020 
1021             // following could be: rfcom_multiplexer_state_machein(..., EVENT_L2CAP_OPENED)
1022 
1023             if (multiplexer->state == RFCOMM_MULTIPLEXER_W4_CONNECT) {
1024                 log_info("L2CAP_EVENT_CHANNEL_OPENED: outgoing connection");
1025                 // wrong remote addr
1026                 if (bd_addr_cmp(event_addr, multiplexer->remote_addr)) break;
1027                 multiplexer->l2cap_cid = l2cap_cid;
1028                 multiplexer->con_handle = con_handle;
1029                 // send SABM #0
1030                 rfcomm_multiplexer_set_state_and_request_can_send_now_event(multiplexer, RFCOMM_MULTIPLEXER_SEND_SABM_0);
1031 
1032             } else { // multiplexer->state == RFCOMM_MULTIPLEXER_W4_SABM_0
1033 
1034                 // set max frame size based on l2cap MTU
1035                 multiplexer->max_frame_size = rfcomm_max_frame_size_for_l2cap_mtu(little_endian_read_16(packet, 17));
1036             }
1037             return 1;
1038 
1039             // l2cap disconnect -> state = RFCOMM_MULTIPLEXER_CLOSED;
1040 
1041         // Notify channel packet handler if they can send now
1042         case L2CAP_EVENT_CAN_SEND_NOW:
1043             l2cap_cid = l2cap_event_can_send_now_get_local_cid(packet);
1044             rfcomm_handle_can_send_now(l2cap_cid);
1045             return 1;
1046 
1047         case L2CAP_EVENT_CHANNEL_CLOSED:
1048             // data: event (8), len(8), channel (16)
1049             l2cap_cid = little_endian_read_16(packet, 2);
1050             multiplexer = rfcomm_multiplexer_for_l2cap_cid(l2cap_cid);
1051             log_info("L2CAP_EVENT_CHANNEL_CLOSED cid 0x%0x, mult %p", l2cap_cid, multiplexer);
1052             if (!multiplexer) break;
1053             log_info("L2CAP_EVENT_CHANNEL_CLOSED state %u", multiplexer->state);
1054             // no need to call l2cap_disconnect here, as it's already closed
1055             rfcomm_multiplexer_finalize(multiplexer);
1056             return 1;
1057 
1058         default:
1059             break;
1060     }
1061     return 0;
1062 }
1063 
1064 static int rfcomm_multiplexer_l2cap_packet_handler(uint16_t channel, uint8_t *packet, uint16_t size){
1065     // get or create a multiplexer for a certain device
1066     rfcomm_multiplexer_t *multiplexer = rfcomm_multiplexer_for_l2cap_cid(channel);
1067     if (!multiplexer) return 0;
1068 
1069     uint16_t l2cap_cid = multiplexer->l2cap_cid;
1070 
1071 	// but only care for multiplexer control channel
1072     uint8_t frame_dlci = packet[0] >> 2;
1073     if (frame_dlci) return 0;
1074     const uint8_t length_offset = (packet[2] & 1) ^ 1;  // to be used for pos >= 3
1075     const uint8_t credit_offset = ((packet[1] & BT_RFCOMM_UIH_PF) == BT_RFCOMM_UIH_PF) ? 1 : 0;   // credits for uih_pf frames
1076     const uint8_t payload_offset = 3 + length_offset + credit_offset;
1077     switch (packet[1]){
1078 
1079         case BT_RFCOMM_SABM:
1080             if (multiplexer->state == RFCOMM_MULTIPLEXER_W4_SABM_0){
1081                 log_info("Received SABM #0");
1082                 multiplexer->outgoing = 0;
1083                 rfcomm_multiplexer_set_state_and_request_can_send_now_event(multiplexer, RFCOMM_MULTIPLEXER_SEND_UA_0);
1084                 return 1;
1085             }
1086             break;
1087 
1088         case BT_RFCOMM_UA:
1089             if (multiplexer->state == RFCOMM_MULTIPLEXER_W4_UA_0) {
1090                 // UA #0 -> send UA #0, state = RFCOMM_MULTIPLEXER_OPEN
1091                 log_info("Received UA #0 ");
1092                 rfcomm_multiplexer_opened(multiplexer);
1093                 return 1;
1094             }
1095             break;
1096 
1097         case BT_RFCOMM_DISC:
1098             // DISC #0 -> send UA #0, close multiplexer
1099             log_info("Received DISC #0, (ougoing = %u)", multiplexer->outgoing);
1100             rfcomm_multiplexer_set_state_and_request_can_send_now_event(multiplexer, RFCOMM_MULTIPLEXER_SEND_UA_0_AND_DISC);
1101             return 1;
1102 
1103         case BT_RFCOMM_DM:
1104             // DM #0 - we shouldn't get this, just give up
1105             log_info("Received DM #0");
1106             log_info("-> Closing down multiplexer");
1107             rfcomm_multiplexer_finalize(multiplexer);
1108             l2cap_disconnect(l2cap_cid, 0x13);
1109             return 1;
1110 
1111         case BT_RFCOMM_UIH:
1112             if (packet[payload_offset] == BT_RFCOMM_CLD_CMD){
1113                 // Multiplexer close down (CLD) -> close mutliplexer
1114                 log_info("Received Multiplexer close down command");
1115                 log_info("-> Closing down multiplexer");
1116                 rfcomm_multiplexer_finalize(multiplexer);
1117                 l2cap_disconnect(l2cap_cid, 0x13);
1118                 return 1;
1119             }
1120             switch (packet[payload_offset]){
1121                 case BT_RFCOMM_CLD_CMD:
1122                      // Multiplexer close down (CLD) -> close mutliplexer
1123                     log_info("Received Multiplexer close down command");
1124                     log_info("-> Closing down multiplexer");
1125                     rfcomm_multiplexer_finalize(multiplexer);
1126                     l2cap_disconnect(l2cap_cid, 0x13);
1127                     return 1;
1128 
1129                 case BT_RFCOMM_FCON_CMD:
1130                     multiplexer->fcon = 0x81;
1131                     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1132                     return 1;
1133 
1134                 case BT_RFCOMM_FCOFF_CMD:
1135                     multiplexer->fcon = 0x80;
1136                     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1137                     return 1;
1138 
1139                 case BT_RFCOMM_TEST_CMD: {
1140                     log_info("Received test command");
1141                     int len = packet[payload_offset+1] >> 1; // length < 125
1142                     if (len > RFCOMM_TEST_DATA_MAX_LEN){
1143                         len = RFCOMM_TEST_DATA_MAX_LEN;
1144                     }
1145                     len = btstack_min(len, size - 1 - payload_offset);  // avoid information leak
1146                     multiplexer->test_data_len = len;
1147                     memcpy(multiplexer->test_data, &packet[payload_offset + 2], len);
1148                     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1149                     return 1;
1150                 }
1151                 default:
1152                     break;
1153             }
1154             break;
1155 
1156         default:
1157             break;
1158 
1159     }
1160     return 0;
1161 }
1162 
1163 static int rfcomm_multiplexer_ready_to_send(rfcomm_multiplexer_t * multiplexer){
1164     if (multiplexer->send_dm_for_dlci) return 1;
1165     if (multiplexer->nsc_command) return 1;
1166     if (multiplexer->fcon & 0x80) return 1;
1167     switch (multiplexer->state){
1168         case RFCOMM_MULTIPLEXER_SEND_SABM_0:
1169         case RFCOMM_MULTIPLEXER_SEND_UA_0:
1170         case RFCOMM_MULTIPLEXER_SEND_UA_0_AND_DISC:
1171             return 1;
1172         case RFCOMM_MULTIPLEXER_OPEN:
1173             if (multiplexer->test_data_len) {
1174                 return 1;
1175             }
1176             break;
1177         default:
1178             break;
1179     }
1180     return 0;
1181 }
1182 
1183 static void rfcomm_multiplexer_state_machine(rfcomm_multiplexer_t * multiplexer, RFCOMM_MULTIPLEXER_EVENT event){
1184 
1185     if (event != MULT_EV_READY_TO_SEND) return;
1186 
1187     uint16_t l2cap_cid = multiplexer->l2cap_cid;
1188 
1189     // process stored DM responses
1190     if (multiplexer->send_dm_for_dlci){
1191         uint8_t dlci = multiplexer->send_dm_for_dlci;
1192         multiplexer->send_dm_for_dlci = 0;
1193         rfcomm_send_dm_pf(multiplexer, dlci);
1194         return;
1195     }
1196 
1197     if (multiplexer->nsc_command){
1198         uint8_t command = multiplexer->nsc_command;
1199         multiplexer->nsc_command = 0;
1200         rfcomm_send_uih_nsc_rsp(multiplexer, command);
1201         return;
1202     }
1203 
1204     if (multiplexer->fcon & 0x80){
1205         multiplexer->fcon &= 0x01;
1206         rfcomm_send_uih_fc_rsp(multiplexer, multiplexer->fcon);
1207 
1208         if (multiplexer->fcon == 0) return;
1209         // trigger client to send again after sending FCon Response
1210         rfcomm_notify_channel_can_send();
1211         return;
1212     }
1213 
1214     switch (multiplexer->state) {
1215         case RFCOMM_MULTIPLEXER_SEND_SABM_0:
1216             log_info("Sending SABM #0 - (multi 0x%p)", multiplexer);
1217             multiplexer->state = RFCOMM_MULTIPLEXER_W4_UA_0;
1218             rfcomm_send_sabm(multiplexer, 0);
1219             break;
1220         case RFCOMM_MULTIPLEXER_SEND_UA_0:
1221             log_info("Sending UA #0");
1222             multiplexer->state = RFCOMM_MULTIPLEXER_OPEN;
1223             rfcomm_send_ua(multiplexer, 0);
1224 
1225             rfcomm_multiplexer_opened(multiplexer);
1226             break;
1227         case RFCOMM_MULTIPLEXER_SEND_UA_0_AND_DISC:
1228             log_info("Sending UA #0");
1229             log_info("Closing down multiplexer");
1230             multiplexer->state = RFCOMM_MULTIPLEXER_CLOSED;
1231             rfcomm_send_ua(multiplexer, 0);
1232 
1233             rfcomm_multiplexer_finalize(multiplexer);
1234             l2cap_disconnect(l2cap_cid, 0x13);
1235             break;
1236         case RFCOMM_MULTIPLEXER_OPEN:
1237             // respond to test command
1238             if (multiplexer->test_data_len){
1239                 int len = multiplexer->test_data_len;
1240                 log_info("Sending TEST Response with %u bytes", len);
1241                 multiplexer->test_data_len = 0;
1242                 rfcomm_send_uih_test_rsp(multiplexer, multiplexer->test_data, len);
1243                 return;
1244             }
1245             break;
1246         default:
1247             break;
1248     }
1249 }
1250 
1251 // MARK: RFCOMM CHANNEL
1252 
1253 static void rfcomm_channel_send_credits(rfcomm_channel_t *channel, uint8_t credits){
1254     channel->credits_incoming += credits;
1255     rfcomm_send_uih_credits(channel->multiplexer, channel->dlci, credits);
1256 }
1257 
1258 static int rfcomm_channel_can_send(rfcomm_channel_t * channel){
1259     if (!channel->credits_outgoing) return 0;
1260     if ((channel->multiplexer->fcon & 1) == 0) return 0;
1261     return l2cap_can_send_packet_now(channel->multiplexer->l2cap_cid);
1262 }
1263 
1264 static void rfcomm_channel_opened(rfcomm_channel_t *rfChannel){
1265 
1266     log_info("rfcomm_channel_opened!");
1267 
1268     rfChannel->state = RFCOMM_CHANNEL_OPEN;
1269     rfcomm_emit_channel_opened(rfChannel, 0);
1270     rfcomm_emit_port_configuration(rfChannel);
1271 
1272     // remove (potential) timer
1273     rfcomm_multiplexer_t *multiplexer = rfChannel->multiplexer;
1274     if (multiplexer->timer_active) {
1275         btstack_run_loop_remove_timer(&multiplexer->timer);
1276         multiplexer->timer_active = 0;
1277     }
1278     // hack for problem detecting authentication failure
1279     multiplexer->at_least_one_connection = 1;
1280 
1281     // request can send now if channel ready
1282     if (rfcomm_channel_ready_to_send(rfChannel)){
1283         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1284     }
1285 }
1286 
1287 static void rfcomm_channel_packet_handler_uih(rfcomm_multiplexer_t *multiplexer, uint8_t * packet, uint16_t size){
1288     const uint8_t frame_dlci = packet[0] >> 2;
1289     const uint8_t length_offset = (packet[2] & 1) ^ 1;  // to be used for pos >= 3
1290     const uint8_t credit_offset = ((packet[1] & BT_RFCOMM_UIH_PF) == BT_RFCOMM_UIH_PF) ? 1 : 0;   // credits for uih_pf frames
1291     const uint8_t payload_offset = 3 + length_offset + credit_offset;
1292     int request_can_send_now = 0;
1293 
1294     rfcomm_channel_t * channel = rfcomm_channel_for_multiplexer_and_dlci(multiplexer, frame_dlci);
1295     if (!channel) return;
1296 
1297     // handle new outgoing credits
1298     if (packet[1] == BT_RFCOMM_UIH_PF) {
1299 
1300         // add them
1301         uint16_t new_credits = packet[3+length_offset];
1302         channel->credits_outgoing += new_credits;
1303         log_info( "RFCOMM data UIH_PF, new credits channel 0x%02x: %u, now %u", channel->rfcomm_cid, new_credits, channel->credits_outgoing);
1304 
1305         // notify channel statemachine
1306         rfcomm_channel_event_t channel_event = { CH_EVT_RCVD_CREDITS, 0 };
1307         log_debug("rfcomm_channel_state_machine_with_channel, waiting_for_can_send_now %u", channel->waiting_for_can_send_now);
1308         int rfcomm_channel_valid = 1;
1309         rfcomm_channel_state_machine_with_channel(channel, &channel_event, &rfcomm_channel_valid);
1310         if (rfcomm_channel_valid){
1311             if (rfcomm_channel_ready_to_send(channel) || channel->waiting_for_can_send_now){
1312                 request_can_send_now = 1;
1313             }
1314         }
1315     }
1316 
1317     // contains payload?
1318     if (size - 1 > payload_offset){
1319 
1320         // log_info( "RFCOMM data UIH_PF, size %u, channel %p", size-payload_offset-1, rfChannel->connection);
1321 
1322         // decrease incoming credit counter
1323         if (channel->credits_incoming > 0){
1324             channel->credits_incoming--;
1325         }
1326 
1327         // deliver payload
1328         (channel->packet_handler)(RFCOMM_DATA_PACKET, channel->rfcomm_cid,
1329                               &packet[payload_offset], size-payload_offset-1);
1330     }
1331 
1332     // automatically provide new credits to remote device, if no incoming flow control
1333     if (!channel->incoming_flow_control && channel->credits_incoming < 5){
1334         channel->new_credits_incoming = RFCOMM_CREDITS;
1335         request_can_send_now = 1;
1336     }
1337 
1338     if (request_can_send_now){
1339         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1340     }
1341 }
1342 
1343 static void rfcomm_channel_accept_pn(rfcomm_channel_t *channel, rfcomm_channel_event_pn_t *event){
1344     // priority of client request
1345     channel->pn_priority = event->priority;
1346 
1347     // new credits
1348     channel->credits_outgoing = event->credits_outgoing;
1349 
1350     // negotiate max frame size
1351     if (channel->max_frame_size > channel->multiplexer->max_frame_size) {
1352         channel->max_frame_size = channel->multiplexer->max_frame_size;
1353     }
1354     if (channel->max_frame_size > event->max_frame_size) {
1355         channel->max_frame_size = event->max_frame_size;
1356     }
1357 
1358 }
1359 
1360 static void rfcomm_channel_finalize(rfcomm_channel_t *channel){
1361 
1362     rfcomm_multiplexer_t *multiplexer = channel->multiplexer;
1363 
1364     // remove from list
1365     btstack_linked_list_remove( &rfcomm_channels, (btstack_linked_item_t *) channel);
1366 
1367     // free channel
1368     btstack_memory_rfcomm_channel_free(channel);
1369 
1370     // update multiplexer timeout after channel was removed from list
1371     rfcomm_multiplexer_prepare_idle_timer(multiplexer);
1372 }
1373 
1374 static void rfcomm_channel_state_machine_with_dlci(rfcomm_multiplexer_t * multiplexer, uint8_t dlci, const rfcomm_channel_event_t *event){
1375 
1376     // TODO: if client max frame size is smaller than RFCOMM_DEFAULT_SIZE, send PN
1377 
1378 
1379     // lookup existing channel
1380     rfcomm_channel_t * channel = rfcomm_channel_for_multiplexer_and_dlci(multiplexer, dlci);
1381 
1382     // log_info("rfcomm_channel_state_machine_with_dlci lookup dlci #%u = 0x%08x - event %u", dlci, (int) channel, event->type);
1383 
1384     if (channel) {
1385         int rfcomm_channel_valid = 1;
1386         rfcomm_channel_state_machine_with_channel(channel, event, &rfcomm_channel_valid);
1387         if (rfcomm_channel_valid && rfcomm_channel_ready_to_send(channel)){
1388             l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1389         }
1390         return;
1391     }
1392 
1393     // service registered?
1394     rfcomm_service_t * service = rfcomm_service_for_channel(dlci >> 1);
1395     // log_info("rfcomm_channel_state_machine_with_dlci service dlci #%u = 0x%08x", dlci, (int) service);
1396     if (!service) {
1397         // discard request by sending disconnected mode
1398         multiplexer->send_dm_for_dlci = dlci;
1399         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1400         return;
1401     }
1402 
1403     // create channel for some events
1404     switch (event->type) {
1405         case CH_EVT_RCVD_SABM:
1406         case CH_EVT_RCVD_PN:
1407         case CH_EVT_RCVD_RPN_REQ:
1408         case CH_EVT_RCVD_RPN_CMD:
1409             // setup incoming channel
1410             channel = rfcomm_channel_create(multiplexer, service, dlci >> 1);
1411             if (!channel){
1412                 // discard request by sending disconnected mode
1413                 multiplexer->send_dm_for_dlci = dlci;
1414                 l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1415             }
1416             break;
1417         default:
1418             break;
1419     }
1420 
1421     if (!channel) {
1422         // discard request by sending disconnected mode
1423         multiplexer->send_dm_for_dlci = dlci;
1424         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1425         return;
1426     }
1427 
1428     int rfcomm_channel_valid = 1;
1429     rfcomm_channel_state_machine_with_channel(channel, event, &rfcomm_channel_valid);
1430     if (rfcomm_channel_valid && rfcomm_channel_ready_to_send(channel)){
1431         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1432     }
1433 }
1434 
1435 static void rfcomm_channel_packet_handler(rfcomm_multiplexer_t * multiplexer,  uint8_t *packet, uint16_t size){
1436 
1437     UNUSED(size);   // ok: fixed format messages
1438 
1439     // rfcomm: (0) addr [76543 server channel] [2 direction: initiator uses 1] [1 C/R: CMD by initiator = 1] [0 EA=1]
1440     const uint8_t frame_dlci = packet[0] >> 2;
1441     uint8_t message_dlci; // used by commands in UIH(_PF) packets
1442 	uint8_t message_len;  //   "
1443 
1444     // rfcomm: (1) command/control
1445     // -- credits_offset = 1 if command == BT_RFCOMM_UIH_PF
1446     const uint8_t credit_offset = ((packet[1] & BT_RFCOMM_UIH_PF) == BT_RFCOMM_UIH_PF) ? 1 : 0;   // credits for uih_pf frames
1447     // rfcomm: (2) length. if bit 0 is cleared, 2 byte length is used. (little endian)
1448     const uint8_t length_offset = (packet[2] & 1) ^ 1;  // to be used for pos >= 3
1449     // rfcomm: (3+length_offset) credits if credits_offset == 1
1450     // rfcomm: (3+length_offest+credits_offset)
1451     const uint8_t payload_offset = 3 + length_offset + credit_offset;
1452 
1453     rfcomm_channel_event_t event;
1454     rfcomm_channel_event_pn_t event_pn;
1455     rfcomm_channel_event_rpn_t event_rpn;
1456     rfcomm_channel_event_msc_t event_msc;
1457 
1458     // switch by rfcomm message type
1459     switch(packet[1]) {
1460 
1461         case BT_RFCOMM_SABM:
1462             event.type = CH_EVT_RCVD_SABM;
1463             log_info("Received SABM #%u", frame_dlci);
1464             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1465             break;
1466 
1467         case BT_RFCOMM_UA:
1468             event.type = CH_EVT_RCVD_UA;
1469             log_info("Received UA #%u",frame_dlci);
1470             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1471             break;
1472 
1473         case BT_RFCOMM_DISC:
1474             event.type = CH_EVT_RCVD_DISC;
1475             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1476             break;
1477 
1478         case BT_RFCOMM_DM:
1479         case BT_RFCOMM_DM_PF:
1480             event.type = CH_EVT_RCVD_DM;
1481             rfcomm_channel_state_machine_with_dlci(multiplexer, frame_dlci, &event);
1482             break;
1483 
1484         case BT_RFCOMM_UIH_PF:
1485         case BT_RFCOMM_UIH:
1486 
1487             message_len  = packet[payload_offset+1] >> 1;
1488 
1489             switch (packet[payload_offset]) {
1490                 case BT_RFCOMM_PN_CMD:
1491                     message_dlci = packet[payload_offset+2];
1492                     event_pn.super.type = CH_EVT_RCVD_PN;
1493                     event_pn.priority = packet[payload_offset+4];
1494                     event_pn.max_frame_size = little_endian_read_16(packet, payload_offset+6);
1495                     event_pn.credits_outgoing = packet[payload_offset+9];
1496                     log_info("Received UIH Parameter Negotiation Command for #%u, credits %u",
1497                         message_dlci, event_pn.credits_outgoing);
1498                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_pn);
1499                     break;
1500 
1501                 case BT_RFCOMM_PN_RSP:
1502                     message_dlci = packet[payload_offset+2];
1503                     event_pn.super.type = CH_EVT_RCVD_PN_RSP;
1504                     event_pn.priority = packet[payload_offset+4];
1505                     event_pn.max_frame_size = little_endian_read_16(packet, payload_offset+6);
1506                     event_pn.credits_outgoing = packet[payload_offset+9];
1507                     log_info("Received UIH Parameter Negotiation Response max frame %u, credits %u",
1508                             event_pn.max_frame_size, event_pn.credits_outgoing);
1509                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_pn);
1510                     break;
1511 
1512                 case BT_RFCOMM_MSC_CMD:
1513                     message_dlci = packet[payload_offset+2] >> 2;
1514                     event_msc.super.type = CH_EVT_RCVD_MSC_CMD;
1515                     event_msc.modem_status = packet[payload_offset+3];
1516                     log_info("Received MSC CMD for #%u, ", message_dlci);
1517                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_msc);
1518                     break;
1519 
1520                 case BT_RFCOMM_MSC_RSP:
1521                     message_dlci = packet[payload_offset+2] >> 2;
1522                     event.type = CH_EVT_RCVD_MSC_RSP;
1523                     log_info("Received MSC RSP for #%u", message_dlci);
1524                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, &event);
1525                     break;
1526 
1527                 case BT_RFCOMM_RPN_CMD:
1528                     message_dlci = packet[payload_offset+2] >> 2;
1529                     switch (message_len){
1530                         case 1:
1531                             log_info("Received Remote Port Negotiation Request for #%u", message_dlci);
1532                             event.type = CH_EVT_RCVD_RPN_REQ;
1533                             rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, &event);
1534                             break;
1535                         case 8:
1536                             log_info("Received Remote Port Negotiation Update for #%u", message_dlci);
1537                             event_rpn.super.type = CH_EVT_RCVD_RPN_CMD;
1538                             event_rpn.data = *(rfcomm_rpn_data_t*) &packet[payload_offset+3];
1539                             rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_rpn);
1540                             break;
1541                         default:
1542                             break;
1543                     }
1544                     break;
1545 
1546                 case BT_RFCOMM_RPN_RSP:
1547                     log_info("Received RPN response");
1548                     break;
1549 
1550                 case BT_RFCOMM_RLS_CMD: {
1551                     log_info("Received RLS command");
1552                     message_dlci = packet[payload_offset+2] >> 2;
1553                     rfcomm_channel_event_rls_t event_rls;
1554                     event_rls.super.type = CH_EVT_RCVD_RLS_CMD;
1555                     event_rls.line_status = packet[payload_offset+3];
1556                     rfcomm_channel_state_machine_with_dlci(multiplexer, message_dlci, (rfcomm_channel_event_t*) &event_rls);
1557                     break;
1558                 }
1559 
1560                 case BT_RFCOMM_RLS_RSP:
1561                     log_info("Received RLS response");
1562                     break;
1563 
1564                 // Following commands are handled by rfcomm_multiplexer_l2cap_packet_handler
1565                 // case BT_RFCOMM_TEST_CMD:
1566                 // case BT_RFCOMM_FCOFF_CMD:
1567                 // case BT_RFCOMM_FCON_CMD:
1568                 // everything else is an not supported command
1569                 default: {
1570                     log_error("Received unknown UIH command packet - 0x%02x", packet[payload_offset]);
1571                     multiplexer->nsc_command = packet[payload_offset];
1572                     break;
1573                 }
1574             }
1575             break;
1576 
1577         default:
1578             log_error("Received unknown RFCOMM message type %x", packet[1]);
1579             break;
1580     }
1581 
1582     // trigger next action - example W4_PN_RSP: transition to SEND_SABM which only depends on "can send"
1583     if (rfcomm_multiplexer_ready_to_send(multiplexer)){
1584         l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
1585     }
1586 }
1587 
1588 static void rfcomm_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
1589 
1590     if (packet_type == HCI_EVENT_PACKET){
1591         rfcomm_hci_event_handler(packet, size);
1592         return;
1593     }
1594 
1595     // we only handle l2cap packets for:
1596     if (packet_type != L2CAP_DATA_PACKET) return;
1597 
1598     //  - multiplexer itself
1599     int handled = rfcomm_multiplexer_l2cap_packet_handler(channel, packet, size);
1600 
1601     if (handled) return;
1602 
1603     // - channel over open mutliplexer
1604     rfcomm_multiplexer_t * multiplexer = rfcomm_multiplexer_for_l2cap_cid(channel);
1605     if (!multiplexer || multiplexer->state != RFCOMM_MULTIPLEXER_OPEN) return;
1606 
1607     // channel data ?
1608     // rfcomm: (0) addr [76543 server channel] [2 direction: initiator uses 1] [1 C/R: CMD by initiator = 1] [0 EA=1]
1609     const uint8_t frame_dlci = packet[0] >> 2;
1610 
1611     if (frame_dlci && (packet[1] == BT_RFCOMM_UIH || packet[1] == BT_RFCOMM_UIH_PF)) {
1612         rfcomm_channel_packet_handler_uih(multiplexer, packet, size);
1613         return;
1614     }
1615 
1616     rfcomm_channel_packet_handler(multiplexer, packet, size);
1617 }
1618 
1619 static int rfcomm_channel_ready_for_open(rfcomm_channel_t *channel){
1620     // note: exchanging MSC isn't neccessary to consider channel open
1621     // note: having outgoing credits is also not necessary to consider channel open
1622     // 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);
1623     // if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_RSP) == 0) return 0;
1624     // if (channel->credits_outgoing == 0) return 0;
1625     log_info("rfcomm_channel_ready_for_open state %u, flags needed %04x, current %04x, rf credits %u",
1626          channel->state, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP, channel->state_var, channel->credits_outgoing);
1627     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP) == 0) return 0;
1628     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SENT_CREDITS) == 0) return 0;
1629 
1630     return 1;
1631 }
1632 
1633 static int rfcomm_channel_ready_for_incoming_dlc_setup(rfcomm_channel_t * channel){
1634     log_info("rfcomm_channel_ready_for_incoming_dlc_setup state var %04x", channel->state_var);
1635     // Client accept and SABM/UA is required, PN RSP is needed if PN was received
1636     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED) == 0) return 0;
1637     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM      ) == 0) return 0;
1638     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_UA        ) != 0) return 0;
1639     if ((channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP    ) != 0) return 0;
1640     return 1;
1641 }
1642 
1643 inline static void rfcomm_channel_state_add(rfcomm_channel_t *channel, RFCOMM_CHANNEL_STATE_VAR event){
1644     channel->state_var = (RFCOMM_CHANNEL_STATE_VAR) (channel->state_var | event);
1645 }
1646 inline static void rfcomm_channel_state_remove(rfcomm_channel_t *channel, RFCOMM_CHANNEL_STATE_VAR event){
1647     channel->state_var = (RFCOMM_CHANNEL_STATE_VAR) (channel->state_var & ~event);
1648 }
1649 
1650 static int rfcomm_channel_ready_to_send(rfcomm_channel_t * channel){
1651     switch (channel->state){
1652         case RFCOMM_CHANNEL_SEND_UIH_PN:
1653             log_debug("ch-ready: state %u", channel->state);
1654             return 1;
1655         case RFCOMM_CHANNEL_SEND_SABM_W4_UA:
1656             log_debug("ch-ready: state %u", channel->state);
1657             return 1;
1658         case RFCOMM_CHANNEL_SEND_UA_AFTER_DISC:
1659             log_debug("ch-ready: state %u", channel->state);
1660             return 1;
1661         case RFCOMM_CHANNEL_SEND_DISC:
1662             log_debug("ch-ready: state %u", channel->state);
1663             return 1;
1664         case RFCOMM_CHANNEL_SEND_DM:
1665             log_debug("ch-ready: state %u", channel->state);
1666             return 1;
1667         case RFCOMM_CHANNEL_OPEN:
1668             if (channel->new_credits_incoming) {
1669                 log_debug("ch-ready: channel open & new_credits_incoming") ;
1670                 return 1;
1671             }
1672             break;
1673         case RFCOMM_CHANNEL_DLC_SETUP:
1674             if (channel->state_var & (
1675                 RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD  |
1676                 RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS
1677              )) {
1678                 log_debug("ch-ready: channel dlc setup & send msc cmd or send credits") ;
1679                 return 1;
1680             }
1681             break;
1682 
1683         default:
1684             break;
1685     }
1686 
1687     if (channel->state_var & (
1688         RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP   |
1689         RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_INFO |
1690         RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP  |
1691         RFCOMM_CHANNEL_STATE_VAR_SEND_UA       |
1692         RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP
1693                              )){
1694         log_debug("ch-ready: state %x, state var %x", channel->state, channel->state_var);
1695         return 1;
1696     }
1697 
1698     if (channel->rls_line_status != RFCOMM_RLS_STATUS_INVALID) {
1699         log_debug("ch-ready: rls_line_status");
1700         return 1;
1701     }
1702 
1703     return 0;
1704 }
1705 
1706 
1707 static void rfcomm_channel_state_machine_with_channel(rfcomm_channel_t *channel, const rfcomm_channel_event_t *event, int * out_channel_valid){
1708 
1709     // log_info("rfcomm_channel_state_machine_with_channel: state %u, state_var %04x, event %u", channel->state, channel->state_var ,event->type);
1710 
1711     // channel != NULL -> channel valid
1712     *out_channel_valid = 1;
1713 
1714     rfcomm_multiplexer_t *multiplexer = channel->multiplexer;
1715 
1716     // TODO: integrate in common switch
1717     if (event->type == CH_EVT_RCVD_DISC){
1718         rfcomm_emit_channel_closed(channel);
1719         channel->state = RFCOMM_CHANNEL_SEND_UA_AFTER_DISC;
1720         return;
1721     }
1722 
1723     // TODO: integrate in common switch
1724     if (event->type == CH_EVT_RCVD_DM){
1725         log_info("Received DM message for #%u", channel->dlci);
1726         log_info("-> Closing channel locally for #%u", channel->dlci);
1727         rfcomm_emit_channel_closed(channel);
1728         rfcomm_channel_finalize(channel);
1729         *out_channel_valid = 0;
1730         return;
1731     }
1732 
1733     // remote port negotiation command - just accept everything for now
1734     //
1735     // "The RPN command can be used before a new DLC is opened and should be used whenever the port settings change."
1736     // "The RPN command is specified as optional in TS 07.10, but it is mandatory to recognize and respond to it in RFCOMM.
1737     //   (Although the handling of individual settings are implementation-dependent.)"
1738     //
1739 
1740     // TODO: integrate in common switch
1741     if (event->type == CH_EVT_RCVD_RPN_CMD){
1742         // control port parameters
1743         rfcomm_channel_event_rpn_t *event_rpn = (rfcomm_channel_event_rpn_t*) event;
1744         rfcomm_rpn_data_update(&channel->rpn_data, &event_rpn->data);
1745         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP);
1746         // notify client about new settings
1747         rfcomm_emit_port_configuration(channel);
1748         return;
1749     }
1750 
1751     // TODO: integrate in common switch
1752     if (event->type == CH_EVT_RCVD_RPN_REQ){
1753         // no values got accepted (no values have beens sent)
1754         channel->rpn_data.parameter_mask_0 = 0x00;
1755         channel->rpn_data.parameter_mask_1 = 0x00;
1756         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP);
1757         return;
1758     }
1759 
1760     if (event->type == CH_EVT_RCVD_RLS_CMD){
1761         rfcomm_channel_event_rls_t * event_rls = (rfcomm_channel_event_rls_t*) event;
1762         channel->rls_line_status = event_rls->line_status & 0x0f;
1763         log_info("CH_EVT_RCVD_RLS_CMD setting line status to 0x%0x", channel->rls_line_status);
1764         rfcomm_emit_remote_line_status(channel, event_rls->line_status);
1765         return;
1766     }
1767 
1768     // TODO: integrate in common switch
1769     if (event->type == CH_EVT_READY_TO_SEND){
1770         if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP){
1771             log_info("Sending Remote Port Negotiation RSP for #%u", channel->dlci);
1772             rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_RPN_RSP);
1773             rfcomm_send_uih_rpn_rsp(multiplexer, channel->dlci, &channel->rpn_data);
1774             return;
1775         }
1776         if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP){
1777             log_info("Sending MSC RSP for #%u", channel->dlci);
1778             rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP);
1779             rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_RSP);
1780             rfcomm_send_uih_msc_rsp(multiplexer, channel->dlci, 0x8d);  // ea=1,fc=0,rtc=1,rtr=1,ic=0,dv=1
1781             return;
1782         }
1783         if (channel->rls_line_status != RFCOMM_RLS_STATUS_INVALID){
1784             log_info("Sending RLS RSP 0x%0x", channel->rls_line_status);
1785             uint8_t line_status = channel->rls_line_status;
1786             channel->rls_line_status = RFCOMM_RLS_STATUS_INVALID;
1787             rfcomm_send_uih_rls_rsp(multiplexer, channel->dlci, line_status);
1788             return;
1789         }
1790     }
1791 
1792     // emit MSC status to app
1793     if (event->type == CH_EVT_RCVD_MSC_CMD){
1794         // notify client about new settings
1795         rfcomm_channel_event_msc_t *event_msc = (rfcomm_channel_event_msc_t*) event;
1796         uint8_t modem_status_event[2+1];
1797         modem_status_event[0] = RFCOMM_EVENT_REMOTE_MODEM_STATUS;
1798         modem_status_event[1] = 1;
1799         modem_status_event[2] = event_msc->modem_status;
1800         (channel->packet_handler)(HCI_EVENT_PACKET, channel->rfcomm_cid, (uint8_t*)&modem_status_event, sizeof(modem_status_event));
1801         // no return, MSC_CMD will be handled by state machine below
1802     }
1803 
1804     rfcomm_channel_event_pn_t * event_pn = (rfcomm_channel_event_pn_t*) event;
1805 
1806     switch (channel->state) {
1807         case RFCOMM_CHANNEL_CLOSED:
1808             switch (event->type){
1809                 case CH_EVT_RCVD_SABM:
1810                     log_info("-> Inform app");
1811                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM);
1812                     channel->state = RFCOMM_CHANNEL_INCOMING_SETUP;
1813                     rfcomm_emit_connection_request(channel);
1814                     break;
1815                 case CH_EVT_RCVD_PN:
1816                     rfcomm_channel_accept_pn(channel, event_pn);
1817                     log_info("-> Inform app");
1818                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_PN);
1819                     channel->state = RFCOMM_CHANNEL_INCOMING_SETUP;
1820                     rfcomm_emit_connection_request(channel);
1821                     break;
1822                 default:
1823                     break;
1824             }
1825             break;
1826 
1827         case RFCOMM_CHANNEL_INCOMING_SETUP:
1828             switch (event->type){
1829                 case CH_EVT_RCVD_SABM:
1830                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM);
1831                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED) {
1832                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_UA);
1833                     }
1834                     break;
1835                 case CH_EVT_RCVD_PN:
1836                     rfcomm_channel_accept_pn(channel, event_pn);
1837                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_PN);
1838                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED) {
1839                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP);
1840                     }
1841                     break;
1842                 case CH_EVT_READY_TO_SEND:
1843                     // if / else if is used to check for state transition after sending
1844                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP){
1845                         log_info("Sending UIH Parameter Negotiation Respond for #%u", channel->dlci);
1846                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP);
1847                         rfcomm_send_uih_pn_response(multiplexer, channel->dlci, channel->pn_priority, channel->max_frame_size);
1848                     } else if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_UA){
1849                         log_info("Sending UA #%u", channel->dlci);
1850                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_UA);
1851                         rfcomm_send_ua(multiplexer, channel->dlci);
1852                     }
1853                     if (rfcomm_channel_ready_for_incoming_dlc_setup(channel)){
1854                         log_info("Incomping setup done, requesting send MSC CMD and send Credits");
1855                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD);
1856                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS);
1857                         channel->state = RFCOMM_CHANNEL_DLC_SETUP;
1858                      }
1859                     break;
1860                 default:
1861                     break;
1862             }
1863             break;
1864 
1865         case RFCOMM_CHANNEL_W4_MULTIPLEXER:
1866             switch (event->type) {
1867                 case CH_EVT_MULTIPLEXER_READY:
1868                     log_info("Muliplexer opened, sending UIH PN next");
1869                     channel->state = RFCOMM_CHANNEL_SEND_UIH_PN;
1870                     break;
1871                 default:
1872                     break;
1873             }
1874             break;
1875 
1876         case RFCOMM_CHANNEL_SEND_UIH_PN:
1877             switch (event->type) {
1878                 case CH_EVT_READY_TO_SEND:
1879                     log_info("Sending UIH Parameter Negotiation Command for #%u (channel 0x%p)", channel->dlci, channel );
1880                     channel->state = RFCOMM_CHANNEL_W4_PN_RSP;
1881                     rfcomm_send_uih_pn_command(multiplexer, channel->dlci, channel->max_frame_size);
1882                     break;
1883                 default:
1884                     break;
1885             }
1886             break;
1887 
1888         case RFCOMM_CHANNEL_W4_PN_RSP:
1889             switch (event->type){
1890                 case CH_EVT_RCVD_PN_RSP:
1891                     // update max frame size
1892                     if (channel->max_frame_size > event_pn->max_frame_size) {
1893                         channel->max_frame_size = event_pn->max_frame_size;
1894                     }
1895                     // new credits
1896                     channel->credits_outgoing = event_pn->credits_outgoing;
1897                     channel->state = RFCOMM_CHANNEL_SEND_SABM_W4_UA;
1898                     break;
1899                 default:
1900                     break;
1901             }
1902             break;
1903 
1904         case RFCOMM_CHANNEL_SEND_SABM_W4_UA:
1905             switch (event->type) {
1906                 case CH_EVT_READY_TO_SEND:
1907                     log_info("Sending SABM #%u", channel->dlci);
1908                     channel->state = RFCOMM_CHANNEL_W4_UA;
1909                     rfcomm_send_sabm(multiplexer, channel->dlci);
1910                     break;
1911                 default:
1912                     break;
1913             }
1914             break;
1915 
1916         case RFCOMM_CHANNEL_W4_UA:
1917             switch (event->type){
1918                 case CH_EVT_RCVD_UA:
1919                     channel->state = RFCOMM_CHANNEL_DLC_SETUP;
1920                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD);
1921                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS);
1922                     break;
1923                 default:
1924                     break;
1925             }
1926             break;
1927 
1928         case RFCOMM_CHANNEL_DLC_SETUP:
1929             switch (event->type){
1930                 case CH_EVT_RCVD_MSC_CMD:
1931                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_CMD);
1932                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP);
1933                     break;
1934                 case CH_EVT_RCVD_MSC_RSP:
1935                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_RCVD_MSC_RSP);
1936                     break;
1937 
1938                 case CH_EVT_READY_TO_SEND:
1939                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD){
1940                         log_info("Sending MSC CMD for #%u", channel->dlci);
1941                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_CMD);
1942                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SENT_MSC_CMD);
1943                         rfcomm_send_uih_msc_cmd(multiplexer, channel->dlci , 0x8d);  // ea=1,fc=0,rtc=1,rtr=1,ic=0,dv=1
1944                         break;
1945                     }
1946                     if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS){
1947                         log_info("Providing credits for #%u", channel->dlci);
1948                         rfcomm_channel_state_remove(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_CREDITS);
1949                         rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SENT_CREDITS);
1950 
1951                         if (channel->new_credits_incoming) {
1952                             uint8_t new_credits = channel->new_credits_incoming;
1953                             channel->new_credits_incoming = 0;
1954                             rfcomm_channel_send_credits(channel, new_credits);
1955                         }
1956                         break;
1957 
1958                     }
1959                     break;
1960                 default:
1961                     break;
1962             }
1963             // finally done?
1964             if (rfcomm_channel_ready_for_open(channel)){
1965                 channel->state = RFCOMM_CHANNEL_OPEN;
1966                 rfcomm_channel_opened(channel);
1967             }
1968             break;
1969 
1970         case RFCOMM_CHANNEL_OPEN:
1971             switch (event->type){
1972                 case CH_EVT_RCVD_MSC_CMD:
1973                     rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_MSC_RSP);
1974                     break;
1975                 case CH_EVT_READY_TO_SEND:
1976                     if (channel->new_credits_incoming) {
1977                         uint8_t new_credits = channel->new_credits_incoming;
1978                         channel->new_credits_incoming = 0;
1979                         rfcomm_channel_send_credits(channel, new_credits);
1980                         break;
1981                     }
1982                     break;
1983                 case CH_EVT_RCVD_CREDITS:
1984                     rfcomm_notify_channel_can_send();
1985                     break;
1986                 default:
1987                     break;
1988             }
1989             break;
1990 
1991         case RFCOMM_CHANNEL_SEND_DM:
1992             switch (event->type) {
1993                 case CH_EVT_READY_TO_SEND:
1994                     log_info("Sending DM_PF for #%u", channel->dlci);
1995                     // don't emit channel closed - channel was never open
1996                     channel->state = RFCOMM_CHANNEL_CLOSED;
1997                     rfcomm_send_dm_pf(multiplexer, channel->dlci);
1998                     rfcomm_channel_finalize(channel);
1999                     *out_channel_valid = 0;
2000                     break;
2001                 default:
2002                     break;
2003             }
2004             break;
2005 
2006         case RFCOMM_CHANNEL_SEND_DISC:
2007             switch (event->type) {
2008                 case CH_EVT_READY_TO_SEND:
2009                     channel->state = RFCOMM_CHANNEL_W4_UA_AFTER_DISC;
2010                     rfcomm_send_disc(multiplexer, channel->dlci);
2011                     break;
2012                 default:
2013                     break;
2014             }
2015             break;
2016 
2017         case RFCOMM_CHANNEL_W4_UA_AFTER_DISC:
2018             switch (event->type){
2019                 case CH_EVT_RCVD_UA:
2020                     channel->state = RFCOMM_CHANNEL_CLOSED;
2021                     rfcomm_emit_channel_closed(channel);
2022                     rfcomm_channel_finalize(channel);
2023                     *out_channel_valid = 0;
2024                     break;
2025                 default:
2026                     break;
2027             }
2028             break;
2029 
2030         case RFCOMM_CHANNEL_SEND_UA_AFTER_DISC:
2031             switch (event->type) {
2032                 case CH_EVT_READY_TO_SEND:
2033                     log_info("Sending UA after DISC for #%u", channel->dlci);
2034                     channel->state = RFCOMM_CHANNEL_CLOSED;
2035                     rfcomm_send_ua(multiplexer, channel->dlci);
2036                     rfcomm_channel_finalize(channel);
2037                     *out_channel_valid = 0;
2038                     break;
2039                 default:
2040                     break;
2041             }
2042             break;
2043 
2044         default:
2045             break;
2046     }
2047 }
2048 
2049 // MARK: RFCOMM BTstack API
2050 
2051 void rfcomm_init(void){
2052     rfcomm_client_cid_generator = 0;
2053     rfcomm_multiplexers = NULL;
2054     rfcomm_services     = NULL;
2055     rfcomm_channels     = NULL;
2056     rfcomm_security_level = LEVEL_2;
2057 }
2058 
2059 void rfcomm_set_required_security_level(gap_security_level_t security_level){
2060     rfcomm_security_level = security_level;
2061 }
2062 
2063 int rfcomm_can_send_packet_now(uint16_t rfcomm_cid){
2064     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2065     if (!channel){
2066         log_error("rfcomm_send cid 0x%02x doesn't exist!", rfcomm_cid);
2067         return 0;
2068     }
2069     return rfcomm_channel_can_send(channel);
2070 }
2071 
2072 void rfcomm_request_can_send_now_event(uint16_t rfcomm_cid){
2073     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2074     if (!channel){
2075         log_error("rfcomm_send cid 0x%02x doesn't exist!", rfcomm_cid);
2076         return;
2077     }
2078     channel->waiting_for_can_send_now = 1;
2079     l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2080 }
2081 
2082 static int rfcomm_assert_send_valid(rfcomm_channel_t * channel , uint16_t len){
2083     if (len > channel->max_frame_size){
2084         log_error("rfcomm_send cid 0x%02x, rfcomm data lenght exceeds MTU!", channel->rfcomm_cid);
2085         return RFCOMM_DATA_LEN_EXCEEDS_MTU;
2086     }
2087 
2088     if (!channel->credits_outgoing){
2089         log_info("rfcomm_send cid 0x%02x, no rfcomm outgoing credits!", channel->rfcomm_cid);
2090         return RFCOMM_NO_OUTGOING_CREDITS;
2091     }
2092 
2093     if ((channel->multiplexer->fcon & 1) == 0){
2094         log_info("rfcomm_send cid 0x%02x, aggregate flow off!", channel->rfcomm_cid);
2095         return RFCOMM_AGGREGATE_FLOW_OFF;
2096     }
2097     return 0;
2098 }
2099 
2100 // pre: rfcomm_can_send_packet_now(rfcomm_cid) == true
2101 int rfcomm_reserve_packet_buffer(void){
2102     return l2cap_reserve_packet_buffer();
2103 }
2104 
2105 void rfcomm_release_packet_buffer(void){
2106     l2cap_release_packet_buffer();
2107 }
2108 
2109 uint8_t * rfcomm_get_outgoing_buffer(void){
2110     uint8_t * rfcomm_out_buffer = l2cap_get_outgoing_buffer();
2111     // address + control + length (16) + no credit field
2112     return &rfcomm_out_buffer[4];
2113 }
2114 
2115 uint16_t rfcomm_get_max_frame_size(uint16_t rfcomm_cid){
2116     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2117     if (!channel){
2118         log_error("rfcomm_get_max_frame_size cid 0x%02x doesn't exist!", rfcomm_cid);
2119         return 0;
2120     }
2121     return channel->max_frame_size;
2122 }
2123 
2124 int rfcomm_send_prepared(uint16_t rfcomm_cid, uint16_t len){
2125     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2126     if (!channel){
2127         log_error("rfcomm_send_prepared cid 0x%02x doesn't exist!", rfcomm_cid);
2128         return 0;
2129     }
2130 
2131     int err = rfcomm_assert_send_valid(channel, len);
2132     if (err) return err;
2133     if (!l2cap_can_send_prepared_packet_now(channel->multiplexer->l2cap_cid)){
2134         log_error("rfcomm_send_prepared: l2cap cannot send now");
2135         return BTSTACK_ACL_BUFFERS_FULL;
2136     }
2137 
2138     // send might cause l2cap to emit new credits, update counters first
2139     if (len){
2140         channel->credits_outgoing--;
2141     } else {
2142         log_info("sending empty RFCOMM packet for cid %02x", rfcomm_cid);
2143     }
2144 
2145     int result = rfcomm_send_uih_prepared(channel->multiplexer, channel->dlci, len);
2146 
2147     if (result != 0) {
2148         if (len) {
2149             channel->credits_outgoing++;
2150         }
2151         log_error("rfcomm_send_prepared: error %d", result);
2152         return result;
2153     }
2154 
2155     return result;
2156 }
2157 
2158 int rfcomm_send(uint16_t rfcomm_cid, uint8_t *data, uint16_t len){
2159     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2160     if (!channel){
2161         log_error("cid 0x%02x doesn't exist!", rfcomm_cid);
2162         return ERROR_CODE_UNKNOWN_CONNECTION_IDENTIFIER;
2163     }
2164 
2165     int err = rfcomm_assert_send_valid(channel, len);
2166     if (err) return err;
2167     if (!l2cap_can_send_packet_now(channel->multiplexer->l2cap_cid)){
2168         log_error("rfcomm_send_internal: l2cap cannot send now");
2169         return BTSTACK_ACL_BUFFERS_FULL;
2170     }
2171 
2172     rfcomm_reserve_packet_buffer();
2173     uint8_t * rfcomm_payload = rfcomm_get_outgoing_buffer();
2174     memcpy(rfcomm_payload, data, len);
2175     err = rfcomm_send_prepared(rfcomm_cid, len);
2176     if (err){
2177         rfcomm_release_packet_buffer();
2178     }
2179     return err;
2180 }
2181 
2182 // Sends Local Lnie Status, see LINE_STATUS_..
2183 int rfcomm_send_local_line_status(uint16_t rfcomm_cid, uint8_t line_status){
2184     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2185     if (!channel){
2186         log_error("rfcomm_send_local_line_status cid 0x%02x doesn't exist!", rfcomm_cid);
2187         return 0;
2188     }
2189     return rfcomm_send_uih_rls_cmd(channel->multiplexer, channel->dlci, line_status);
2190 }
2191 
2192 // Sned local modem status. see MODEM_STAUS_..
2193 int rfcomm_send_modem_status(uint16_t rfcomm_cid, uint8_t modem_status){
2194     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2195     if (!channel){
2196         log_error("rfcomm_send_modem_status cid 0x%02x doesn't exist!", rfcomm_cid);
2197         return 0;
2198     }
2199     return rfcomm_send_uih_msc_cmd(channel->multiplexer, channel->dlci, modem_status);
2200 }
2201 
2202 // Configure remote port
2203 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){
2204     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2205     if (!channel){
2206         log_error("rfcomm_send_port_configuration cid 0x%02x doesn't exist!", rfcomm_cid);
2207         return 0;
2208     }
2209     rfcomm_rpn_data_t rpn_data;
2210     rpn_data.baud_rate = baud_rate;
2211     rpn_data.flags = data_bits | (stop_bits << 2) | (parity << 3);
2212     rpn_data.flow_control = flow_control;
2213     rpn_data.xon = 0;
2214     rpn_data.xoff = 0;
2215     rpn_data.parameter_mask_0 = 0x1f;   // all but xon/xoff
2216     rpn_data.parameter_mask_1 = 0x3f;   // all flow control options
2217     return rfcomm_send_uih_rpn_cmd(channel->multiplexer, channel->dlci, &rpn_data);
2218 }
2219 
2220 // Query remote port
2221 int rfcomm_query_port_configuration(uint16_t rfcomm_cid){
2222     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2223     if (!channel){
2224         log_error("rfcomm_query_port_configuration cid 0x%02x doesn't exist!", rfcomm_cid);
2225         return 0;
2226     }
2227     return rfcomm_send_uih_rpn_req(channel->multiplexer, channel->dlci);
2228 }
2229 
2230 
2231 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){
2232     log_info("RFCOMM_CREATE_CHANNEL addr %s channel #%u init credits %u",  bd_addr_to_str(addr), server_channel, initial_credits);
2233 
2234     // create new multiplexer if necessary
2235     uint8_t status = 0;
2236     uint8_t dlci = 0;
2237     int new_multiplexer = 0;
2238     rfcomm_channel_t * channel = NULL;
2239     rfcomm_multiplexer_t * multiplexer = rfcomm_multiplexer_for_addr(addr);
2240     if (!multiplexer) {
2241         multiplexer = rfcomm_multiplexer_create_for_addr(addr);
2242         if (!multiplexer){
2243             status = BTSTACK_MEMORY_ALLOC_FAILED;
2244             goto fail;
2245         }
2246         multiplexer->outgoing = 1;
2247         multiplexer->state = RFCOMM_MULTIPLEXER_W4_CONNECT;
2248         new_multiplexer = 1;
2249     }
2250 
2251     // check if channel for this remote service already exists
2252     dlci = (server_channel << 1) | (multiplexer->outgoing ^ 1);
2253     channel = rfcomm_channel_for_multiplexer_and_dlci(multiplexer, dlci);
2254     if (channel){
2255         status = RFCOMM_CHANNEL_ALREADY_REGISTERED;
2256         goto fail;
2257     }
2258 
2259     // prepare channel
2260     channel = rfcomm_channel_create(multiplexer, NULL, server_channel);
2261     if (!channel){
2262         status = BTSTACK_MEMORY_ALLOC_FAILED;
2263         goto fail;
2264     }
2265 
2266     // rfcomm_cid is already assigned by rfcomm_channel_create
2267     channel->incoming_flow_control = incoming_flow_control;
2268     channel->new_credits_incoming  = initial_credits;
2269     channel->packet_handler = packet_handler;
2270 
2271     // return rfcomm_cid
2272     if (out_rfcomm_cid){
2273         *out_rfcomm_cid = channel->rfcomm_cid;
2274     }
2275 
2276     // start multiplexer setup
2277     if (multiplexer->state != RFCOMM_MULTIPLEXER_OPEN) {
2278         channel->state = RFCOMM_CHANNEL_W4_MULTIPLEXER;
2279         uint16_t l2cap_cid = 0;
2280         status = l2cap_create_channel(rfcomm_packet_handler, addr, BLUETOOTH_PROTOCOL_RFCOMM, l2cap_max_mtu(), &l2cap_cid);
2281         if (status) goto fail;
2282         multiplexer->l2cap_cid = l2cap_cid;
2283         return 0;
2284     }
2285 
2286     channel->state = RFCOMM_CHANNEL_SEND_UIH_PN;
2287 
2288     // start connecting, if multiplexer is already up and running
2289     l2cap_request_can_send_now_event(multiplexer->l2cap_cid);
2290     return 0;
2291 
2292 fail:
2293     if (new_multiplexer) btstack_memory_rfcomm_multiplexer_free(multiplexer);
2294     if (channel)         btstack_memory_rfcomm_channel_free(channel);
2295     return status;
2296 }
2297 
2298 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){
2299     return rfcomm_channel_create_internal(packet_handler, addr, server_channel, 1, initial_credits, out_rfcomm_cid);
2300 }
2301 
2302 uint8_t rfcomm_create_channel(btstack_packet_handler_t packet_handler, bd_addr_t addr, uint8_t server_channel, uint16_t * out_rfcomm_cid){
2303     return rfcomm_channel_create_internal(packet_handler, addr, server_channel, 0, RFCOMM_CREDITS, out_rfcomm_cid);
2304 }
2305 
2306 void rfcomm_disconnect(uint16_t rfcomm_cid){
2307     log_info("RFCOMM_DISCONNECT cid 0x%02x", rfcomm_cid);
2308     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2309     if (!channel) return;
2310 
2311     channel->state = RFCOMM_CHANNEL_SEND_DISC;
2312     l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2313 }
2314 
2315 static uint8_t rfcomm_register_service_internal(btstack_packet_handler_t packet_handler,
2316     uint8_t channel, uint16_t max_frame_size, uint8_t incoming_flow_control, uint8_t initial_credits){
2317 
2318     log_info("RFCOMM_REGISTER_SERVICE channel #%u mtu %u flow_control %u credits %u",
2319              channel, max_frame_size, incoming_flow_control, initial_credits);
2320 
2321     // check if already registered
2322     rfcomm_service_t * service = rfcomm_service_for_channel(channel);
2323     if (service){
2324         return RFCOMM_CHANNEL_ALREADY_REGISTERED;
2325     }
2326 
2327     // alloc structure
2328     service = btstack_memory_rfcomm_service_get();
2329     if (!service) {
2330         return BTSTACK_MEMORY_ALLOC_FAILED;
2331     }
2332 
2333     // register with l2cap if not registered before, max MTU
2334     if (btstack_linked_list_empty(&rfcomm_services)){
2335         l2cap_register_service(rfcomm_packet_handler, BLUETOOTH_PROTOCOL_RFCOMM, 0xffff, rfcomm_security_level);
2336     }
2337 
2338     // fill in
2339     service->packet_handler = packet_handler;
2340     service->server_channel = channel;
2341     service->max_frame_size = max_frame_size;
2342     service->incoming_flow_control = incoming_flow_control;
2343     service->incoming_initial_credits = initial_credits;
2344 
2345     // add to services list
2346     btstack_linked_list_add(&rfcomm_services, (btstack_linked_item_t *) service);
2347 
2348     return 0;
2349 }
2350 
2351 uint8_t rfcomm_register_service_with_initial_credits(btstack_packet_handler_t packet_handler,
2352     uint8_t channel, uint16_t max_frame_size, uint8_t initial_credits){
2353 
2354     return rfcomm_register_service_internal(packet_handler, channel, max_frame_size, 1, initial_credits);
2355 }
2356 
2357 uint8_t rfcomm_register_service(btstack_packet_handler_t packet_handler, uint8_t channel,
2358     uint16_t max_frame_size){
2359 
2360     return rfcomm_register_service_internal(packet_handler, channel, max_frame_size, 0,RFCOMM_CREDITS);
2361 }
2362 
2363 void rfcomm_unregister_service(uint8_t service_channel){
2364     log_info("RFCOMM_UNREGISTER_SERVICE #%u", service_channel);
2365     rfcomm_service_t *service = rfcomm_service_for_channel(service_channel);
2366     if (!service) return;
2367     btstack_linked_list_remove(&rfcomm_services, (btstack_linked_item_t *) service);
2368     btstack_memory_rfcomm_service_free(service);
2369 
2370     // unregister if no services active
2371     if (btstack_linked_list_empty(&rfcomm_services)){
2372         // bt_send_cmd(&l2cap_unregister_service, BLUETOOTH_PROTOCOL_RFCOMM);
2373         l2cap_unregister_service(BLUETOOTH_PROTOCOL_RFCOMM);
2374     }
2375 }
2376 
2377 void rfcomm_accept_connection(uint16_t rfcomm_cid){
2378     log_info("RFCOMM_ACCEPT_CONNECTION cid 0x%02x", rfcomm_cid);
2379     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2380     if (!channel) return;
2381     switch (channel->state) {
2382         case RFCOMM_CHANNEL_INCOMING_SETUP:
2383             rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_CLIENT_ACCEPTED);
2384             if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_PN){
2385                 rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_PN_RSP);
2386                 l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2387             }
2388             if (channel->state_var & RFCOMM_CHANNEL_STATE_VAR_RCVD_SABM){
2389                 rfcomm_channel_state_add(channel, RFCOMM_CHANNEL_STATE_VAR_SEND_UA);
2390                 l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2391             }
2392             // at least one of { PN RSP, UA } needs to be sent
2393             // state transistion incoming setup -> dlc setup happens in rfcomm_run after these have been sent
2394             break;
2395         default:
2396             break;
2397     }
2398 
2399 }
2400 
2401 void rfcomm_decline_connection(uint16_t rfcomm_cid){
2402     log_info("RFCOMM_DECLINE_CONNECTION cid 0x%02x", rfcomm_cid);
2403     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2404     if (!channel) return;
2405     switch (channel->state) {
2406         case RFCOMM_CHANNEL_INCOMING_SETUP:
2407             channel->state = RFCOMM_CHANNEL_SEND_DM;
2408             l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2409             break;
2410         default:
2411             break;
2412     }
2413 }
2414 
2415 void rfcomm_grant_credits(uint16_t rfcomm_cid, uint8_t credits){
2416     log_info("RFCOMM_GRANT_CREDITS cid 0x%02x credits %u", rfcomm_cid, credits);
2417     rfcomm_channel_t * channel = rfcomm_channel_for_rfcomm_cid(rfcomm_cid);
2418     if (!channel) return;
2419     if (!channel->incoming_flow_control) return;
2420     channel->new_credits_incoming += credits;
2421 
2422     // process
2423     l2cap_request_can_send_now_event(channel->multiplexer->l2cap_cid);
2424 }
2425 
2426 
2427