xref: /btstack/src/l2cap.c (revision 2149f12ebb1d2e3920345d1a13efd2a18cb74b53)
1 /*
2  * Copyright (C) 2009 by Matthias Ringwald
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  *
17  * THIS SOFTWARE IS PROVIDED BY MATTHIAS RINGWALD AND CONTRIBUTORS
18  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
19  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
20  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL MATTHIAS
21  * RINGWALD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
22  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
23  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
24  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
25  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
26  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
27  * THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28  * SUCH DAMAGE.
29  *
30  */
31 
32 /*
33  *  l2cap.c
34  *
35  *  Logical Link Control and Adaption Protocl (L2CAP)
36  *
37  *  Created by Matthias Ringwald on 5/16/09.
38  */
39 
40 #include "l2cap.h"
41 #include "hci.h"
42 #include "hci_dump.h"
43 #include "debug.h"
44 #include "btstack_memory.h"
45 
46 #include <stdarg.h>
47 #include <string.h>
48 
49 #include <stdio.h>
50 
51 // nr of buffered acl packets in outgoing queue to get max performance
52 #define NR_BUFFERED_ACL_PACKETS 3
53 
54 // used to cache l2cap rejects, echo, and informational requests
55 #define NR_PENDING_SIGNALING_RESPONSES 3
56 
57 // offsets for L2CAP SIGNALING COMMANDS
58 #define L2CAP_SIGNALING_COMMAND_CODE_OFFSET   0
59 #define L2CAP_SIGNALING_COMMAND_SIGID_OFFSET  1
60 #define L2CAP_SIGNALING_COMMAND_LENGTH_OFFSET 2
61 #define L2CAP_SIGNALING_COMMAND_DATA_OFFSET   4
62 
63 static void null_packet_handler(void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size);
64 static void l2cap_packet_handler(uint8_t packet_type, uint8_t *packet, uint16_t size);
65 
66 // used to cache l2cap rejects, echo, and informational requests
67 static l2cap_signaling_response_t signaling_responses[NR_PENDING_SIGNALING_RESPONSES];
68 static int signaling_responses_pending;
69 
70 static linked_list_t l2cap_channels = NULL;
71 static linked_list_t l2cap_services = NULL;
72 static void (*packet_handler) (void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size) = null_packet_handler;
73 static int new_credits_blocked = 0;
74 
75 static btstack_packet_handler_t attribute_protocol_packet_handler = NULL;
76 static btstack_packet_handler_t security_protocol_packet_handler = NULL;
77 
78 // prototypes
79 static void l2cap_finialize_channel_close(l2cap_channel_t *channel);
80 static l2cap_service_t * l2cap_get_service(uint16_t psm);
81 static void l2cap_emit_channel_opened(l2cap_channel_t *channel, uint8_t status);
82 static void l2cap_emit_channel_closed(l2cap_channel_t *channel);
83 static void l2cap_emit_connection_request(l2cap_channel_t *channel);
84 static int l2cap_channel_ready_for_open(l2cap_channel_t *channel);
85 
86 
87 void l2cap_init(){
88     new_credits_blocked = 0;
89     signaling_responses_pending = 0;
90 
91     l2cap_channels = NULL;
92     l2cap_services = NULL;
93 
94     packet_handler = null_packet_handler;
95 
96     //
97     // register callback with HCI
98     //
99     hci_register_packet_handler(&l2cap_packet_handler);
100     hci_connectable_control(0); // no services yet
101 }
102 
103 
104 /** Register L2CAP packet handlers */
105 static void null_packet_handler(void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
106 }
107 void l2cap_register_packet_handler(void (*handler)(void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size)){
108     packet_handler = handler;
109 }
110 
111 //  notify client/protocol handler
112 void l2cap_dispatch(l2cap_channel_t *channel, uint8_t type, uint8_t * data, uint16_t size){
113     if (channel->packet_handler) {
114         (* (channel->packet_handler))(type, channel->local_cid, data, size);
115     } else {
116         (*packet_handler)(channel->connection, type, channel->local_cid, data, size);
117     }
118 }
119 
120 void l2cap_emit_channel_opened(l2cap_channel_t *channel, uint8_t status) {
121     uint8_t event[21];
122     event[0] = L2CAP_EVENT_CHANNEL_OPENED;
123     event[1] = sizeof(event) - 2;
124     event[2] = status;
125     bt_flip_addr(&event[3], channel->address);
126     bt_store_16(event,  9, channel->handle);
127     bt_store_16(event, 11, channel->psm);
128     bt_store_16(event, 13, channel->local_cid);
129     bt_store_16(event, 15, channel->remote_cid);
130     bt_store_16(event, 17, channel->local_mtu);
131     bt_store_16(event, 19, channel->remote_mtu);
132     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
133     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
134 }
135 
136 void l2cap_emit_channel_closed(l2cap_channel_t *channel) {
137     uint8_t event[4];
138     event[0] = L2CAP_EVENT_CHANNEL_CLOSED;
139     event[1] = sizeof(event) - 2;
140     bt_store_16(event, 2, channel->local_cid);
141     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
142     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
143 }
144 
145 void l2cap_emit_connection_request(l2cap_channel_t *channel) {
146     uint8_t event[16];
147     event[0] = L2CAP_EVENT_INCOMING_CONNECTION;
148     event[1] = sizeof(event) - 2;
149     bt_flip_addr(&event[2], channel->address);
150     bt_store_16(event,  8, channel->handle);
151     bt_store_16(event, 10, channel->psm);
152     bt_store_16(event, 12, channel->local_cid);
153     bt_store_16(event, 14, channel->remote_cid);
154     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
155     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
156 }
157 
158 static void l2cap_emit_service_registered(void *connection, uint8_t status, uint16_t psm){
159     uint8_t event[5];
160     event[0] = L2CAP_EVENT_SERVICE_REGISTERED;
161     event[1] = sizeof(event) - 2;
162     event[2] = status;
163     bt_store_16(event, 3, psm);
164     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
165     (*packet_handler)(connection, HCI_EVENT_PACKET, 0, event, sizeof(event));
166 }
167 
168 void l2cap_emit_credits(l2cap_channel_t *channel, uint8_t credits) {
169     // track credits
170     channel->packets_granted += credits;
171     // log_info("l2cap_emit_credits for cid %u, credits given: %u (+%u)\n", channel->local_cid, channel->packets_granted, credits);
172 
173     uint8_t event[5];
174     event[0] = L2CAP_EVENT_CREDITS;
175     event[1] = sizeof(event) - 2;
176     bt_store_16(event, 2, channel->local_cid);
177     event[4] = credits;
178     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
179     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
180 }
181 
182 void l2cap_block_new_credits(uint8_t blocked){
183     new_credits_blocked = blocked;
184 }
185 
186 void l2cap_hand_out_credits(void){
187 
188     if (new_credits_blocked) return;    // we're told not to. used by daemon
189 
190     linked_item_t *it;
191     for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
192         if (!hci_number_free_acl_slots()) return;
193         l2cap_channel_t * channel = (l2cap_channel_t *) it;
194         if (channel->state != L2CAP_STATE_OPEN) continue;
195         if (hci_number_outgoing_packets(channel->handle) < NR_BUFFERED_ACL_PACKETS && channel->packets_granted == 0) {
196             l2cap_emit_credits(channel, 1);
197         }
198     }
199 }
200 
201 l2cap_channel_t * l2cap_get_channel_for_local_cid(uint16_t local_cid){
202     linked_item_t *it;
203     for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
204         l2cap_channel_t * channel = (l2cap_channel_t *) it;
205         if ( channel->local_cid == local_cid) {
206             return channel;
207         }
208     }
209     return NULL;
210 }
211 
212 int  l2cap_can_send_packet_now(uint16_t local_cid){
213     l2cap_channel_t *channel = l2cap_get_channel_for_local_cid(local_cid);
214     if (!channel) return 0;
215     if (!channel->packets_granted) return 0;
216     return hci_can_send_packet_now(HCI_ACL_DATA_PACKET);
217 }
218 
219 uint16_t l2cap_get_remote_mtu_for_local_cid(uint16_t local_cid){
220     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
221     if (channel) {
222         return channel->remote_mtu;
223     }
224     return 0;
225 }
226 
227 int l2cap_send_signaling_packet(hci_con_handle_t handle, L2CAP_SIGNALING_COMMANDS cmd, uint8_t identifier, ...){
228 
229     if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)){
230         log_info("l2cap_send_signaling_packet, cannot send\n");
231         return BTSTACK_ACL_BUFFERS_FULL;
232     }
233 
234     // log_info("l2cap_send_signaling_packet type %u\n", cmd);
235     uint8_t *acl_buffer = hci_get_outgoing_acl_packet_buffer();
236     va_list argptr;
237     va_start(argptr, identifier);
238     uint16_t len = l2cap_create_signaling_internal(acl_buffer, handle, cmd, identifier, argptr);
239     va_end(argptr);
240     // log_info("l2cap_send_signaling_packet con %u!\n", handle);
241     return hci_send_acl_packet(acl_buffer, len);
242 }
243 
244 uint8_t *l2cap_get_outgoing_buffer(void){
245     return hci_get_outgoing_acl_packet_buffer() + COMPLETE_L2CAP_HEADER; // 8 bytes
246 }
247 
248 int l2cap_send_prepared(uint16_t local_cid, uint16_t len){
249 
250     if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)){
251         log_info("l2cap_send_internal cid %u, cannot send\n", local_cid);
252         return BTSTACK_ACL_BUFFERS_FULL;
253     }
254 
255     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
256     if (!channel) {
257         log_error("l2cap_send_internal no channel for cid %u\n", local_cid);
258         return -1;   // TODO: define error
259     }
260 
261     if (channel->packets_granted == 0){
262         log_error("l2cap_send_internal cid %u, no credits!\n", local_cid);
263         return -1;  // TODO: define error
264     }
265 
266     --channel->packets_granted;
267 
268     log_debug("l2cap_send_internal cid %u, handle %u, 1 credit used, credits left %u;\n",
269                   local_cid, channel->handle, channel->packets_granted);
270 
271     uint8_t *acl_buffer = hci_get_outgoing_acl_packet_buffer();
272 
273     // 0 - Connection handle : PB=10 : BC=00
274     bt_store_16(acl_buffer, 0, channel->handle | (2 << 12) | (0 << 14));
275     // 2 - ACL length
276     bt_store_16(acl_buffer, 2,  len + 4);
277     // 4 - L2CAP packet length
278     bt_store_16(acl_buffer, 4,  len + 0);
279     // 6 - L2CAP channel DEST
280     bt_store_16(acl_buffer, 6, channel->remote_cid);
281     // send
282     int err = hci_send_acl_packet(acl_buffer, len+8);
283 
284     l2cap_hand_out_credits();
285 
286     return err;
287 }
288 
289 int l2cap_send_prepared_connectionless(uint16_t handle, uint16_t cid, uint16_t len){
290 
291     if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)){
292         log_info("l2cap_send_prepared_to_handle cid %u, cannot send\n", cid);
293         return BTSTACK_ACL_BUFFERS_FULL;
294     }
295 
296     log_debug("l2cap_send_prepared_to_handle cid %u, handle %u\n", cid, handle);
297 
298     uint8_t *acl_buffer = hci_get_outgoing_acl_packet_buffer();
299 
300     // 0 - Connection handle : PB=10 : BC=00
301     bt_store_16(acl_buffer, 0, handle | (2 << 12) | (0 << 14));
302     // 2 - ACL length
303     bt_store_16(acl_buffer, 2,  len + 4);
304     // 4 - L2CAP packet length
305     bt_store_16(acl_buffer, 4,  len + 0);
306     // 6 - L2CAP channel DEST
307     bt_store_16(acl_buffer, 6, cid);
308     // send
309     int err = hci_send_acl_packet(acl_buffer, len+8);
310 
311     l2cap_hand_out_credits();
312 
313     return err;
314 }
315 
316 int l2cap_send_internal(uint16_t local_cid, uint8_t *data, uint16_t len){
317 
318     if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)){
319         log_info("l2cap_send_internal cid %u, cannot send\n", local_cid);
320         return BTSTACK_ACL_BUFFERS_FULL;
321     }
322 
323     uint8_t *acl_buffer = hci_get_outgoing_acl_packet_buffer();
324 
325     memcpy(&acl_buffer[8], data, len);
326 
327     return l2cap_send_prepared(local_cid, len);
328 }
329 
330 int l2cap_send_connectionless(uint16_t handle, uint16_t cid, uint8_t *data, uint16_t len){
331 
332     if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)){
333         log_info("l2cap_send_internal cid %u, cannot send\n", cid);
334         return BTSTACK_ACL_BUFFERS_FULL;
335     }
336 
337     uint8_t *acl_buffer = hci_get_outgoing_acl_packet_buffer();
338 
339     memcpy(&acl_buffer[8], data, len);
340 
341     return l2cap_send_prepared_connectionless(handle, cid, len);
342 }
343 
344 static inline void channelStateVarSetFlag(l2cap_channel_t *channel, L2CAP_CHANNEL_STATE_VAR flag){
345     channel->state_var = (L2CAP_CHANNEL_STATE_VAR) (channel->state_var | flag);
346 }
347 
348 static inline void channelStateVarClearFlag(l2cap_channel_t *channel, L2CAP_CHANNEL_STATE_VAR flag){
349     channel->state_var = (L2CAP_CHANNEL_STATE_VAR) (channel->state_var & ~flag);
350 }
351 
352 
353 
354 // MARK: L2CAP_RUN
355 // process outstanding signaling tasks
356 void l2cap_run(void){
357 
358     // check pending signaling responses
359     while (signaling_responses_pending){
360 
361         if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)) break;
362 
363         hci_con_handle_t handle = signaling_responses[0].handle;
364         uint8_t sig_id = signaling_responses[0].sig_id;
365         uint16_t infoType = signaling_responses[0].data;    // INFORMATION_REQUEST
366         uint16_t result   = signaling_responses[0].data;    // CONNECTION_REQUEST
367 
368         switch (signaling_responses[0].code){
369             case CONNECTION_REQUEST:
370                 l2cap_send_signaling_packet(handle, CONNECTION_RESPONSE, sig_id, 0, 0, result, 0);
371                 break;
372             case ECHO_REQUEST:
373                 l2cap_send_signaling_packet(handle, ECHO_RESPONSE, sig_id, 0, NULL);
374                 break;
375             case INFORMATION_REQUEST:
376                 if (infoType == 2) {
377                     uint32_t features = 0;
378                     // extended features request supported, however no features present
379                     l2cap_send_signaling_packet(handle, INFORMATION_RESPONSE, sig_id, infoType, 0, 4, &features);
380                 } else {
381                     // all other types are not supported
382                     l2cap_send_signaling_packet(handle, INFORMATION_RESPONSE, sig_id, infoType, 1, 0, NULL);
383                 }
384                 break;
385             default:
386                 // should not happen
387                 break;
388         }
389 
390         // remove first item
391         signaling_responses_pending--;
392         int i;
393         for (i=0; i < signaling_responses_pending; i++){
394             memcpy(&signaling_responses[i], &signaling_responses[i+1], sizeof(l2cap_signaling_response_t));
395         }
396     }
397 
398     uint8_t  config_options[4];
399     linked_item_t *it;
400     linked_item_t *next;
401     for (it = (linked_item_t *) l2cap_channels; it ; it = next){
402         next = it->next;    // cache next item as current item might get freed
403 
404         if (!hci_can_send_packet_now(HCI_COMMAND_DATA_PACKET)) break;
405         if (!hci_can_send_packet_now(HCI_ACL_DATA_PACKET)) break;
406 
407         l2cap_channel_t * channel = (l2cap_channel_t *) it;
408 
409         // log_info("l2cap_run: state %u, var 0x%02x\n", channel->state, channel->state_var);
410 
411 
412         switch (channel->state){
413 
414             case L2CAP_STATE_WILL_SEND_CREATE_CONNECTION:
415                 // send connection request - set state first
416                 channel->state = L2CAP_STATE_WAIT_CONNECTION_COMPLETE;
417                 // BD_ADDR, Packet_Type, Page_Scan_Repetition_Mode, Reserved, Clock_Offset, Allow_Role_Switch
418                 hci_send_cmd(&hci_create_connection, channel->address, hci_usable_acl_packet_types(), 0, 0, 0, 1);
419                 break;
420 
421             case L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_DECLINE:
422                 l2cap_send_signaling_packet(channel->handle, CONNECTION_RESPONSE, channel->remote_sig_id, 0, 0, channel->reason, 0);
423                 // discard channel - l2cap_finialize_channel_close without sending l2cap close event
424                 linked_list_remove(&l2cap_channels, (linked_item_t *) channel); // -- remove from list
425                 btstack_memory_l2cap_channel_free(channel);
426                 break;
427 
428             case L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_ACCEPT:
429                 channel->state = L2CAP_STATE_CONFIG;
430                 channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
431                 l2cap_send_signaling_packet(channel->handle, CONNECTION_RESPONSE, channel->remote_sig_id, channel->local_cid, channel->remote_cid, 0, 0);
432                 break;
433 
434             case L2CAP_STATE_WILL_SEND_CONNECTION_REQUEST:
435                 // success, start l2cap handshake
436                 channel->local_sig_id = l2cap_next_sig_id();
437                 channel->state = L2CAP_STATE_WAIT_CONNECT_RSP;
438                 l2cap_send_signaling_packet( channel->handle, CONNECTION_REQUEST, channel->local_sig_id, channel->psm, channel->local_cid);
439                 break;
440 
441             case L2CAP_STATE_CONFIG:
442                 if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP){
443                     channelStateVarClearFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP);
444                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SENT_CONF_RSP);
445                     l2cap_send_signaling_packet(channel->handle, CONFIGURE_RESPONSE, channel->remote_sig_id, channel->remote_cid, 0, 0, 0, NULL);
446                 }
447                 else if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ){
448                     channelStateVarClearFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
449                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SENT_CONF_REQ);
450                     channel->local_sig_id = l2cap_next_sig_id();
451                     config_options[0] = 1; // MTU
452                     config_options[1] = 2; // len param
453                     bt_store_16( (uint8_t*)&config_options, 2, channel->local_mtu);
454                     l2cap_send_signaling_packet(channel->handle, CONFIGURE_REQUEST, channel->local_sig_id, channel->remote_cid, 0, 4, &config_options);
455                 }
456                 if (l2cap_channel_ready_for_open(channel)){
457                     channel->state = L2CAP_STATE_OPEN;
458                     l2cap_emit_channel_opened(channel, 0);  // success
459                     l2cap_emit_credits(channel, 1);
460                 }
461                 break;
462 
463             case L2CAP_STATE_WILL_SEND_DISCONNECT_RESPONSE:
464                 l2cap_send_signaling_packet( channel->handle, DISCONNECTION_RESPONSE, channel->remote_sig_id, channel->local_cid, channel->remote_cid);
465                 l2cap_finialize_channel_close(channel);  // -- remove from list
466                 break;
467 
468             case L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST:
469                 channel->local_sig_id = l2cap_next_sig_id();
470                 channel->state = L2CAP_STATE_WAIT_DISCONNECT;
471                 l2cap_send_signaling_packet( channel->handle, DISCONNECTION_REQUEST, channel->local_sig_id, channel->remote_cid, channel->local_cid);
472                 break;
473             default:
474                 break;
475         }
476     }
477 }
478 
479 uint16_t l2cap_max_mtu(void){
480     return hci_max_acl_data_packet_length() - L2CAP_HEADER_SIZE;
481 }
482 
483 // open outgoing L2CAP channel
484 void l2cap_create_channel_internal(void * connection, btstack_packet_handler_t packet_handler,
485                                    bd_addr_t address, uint16_t psm, uint16_t mtu){
486 
487     // alloc structure
488     l2cap_channel_t * chan = (l2cap_channel_t*) btstack_memory_l2cap_channel_get();
489     if (!chan) {
490         // emit error event
491         l2cap_channel_t dummy_channel;
492         BD_ADDR_COPY(dummy_channel.address, address);
493         dummy_channel.psm = psm;
494         l2cap_emit_channel_opened(&dummy_channel, BTSTACK_MEMORY_ALLOC_FAILED);
495         return;
496     }
497     // limit local mtu to max acl packet length
498     if (mtu > l2cap_max_mtu()) {
499         mtu = l2cap_max_mtu();
500     }
501 
502     // fill in
503     BD_ADDR_COPY(chan->address, address);
504     chan->psm = psm;
505     chan->handle = 0;
506     chan->connection = connection;
507     chan->packet_handler = packet_handler;
508     chan->remote_mtu = L2CAP_MINIMAL_MTU;
509     chan->local_mtu = mtu;
510     chan->packets_granted = 0;
511 
512     // set initial state
513     chan->state = L2CAP_STATE_WILL_SEND_CREATE_CONNECTION;
514     chan->state_var = L2CAP_CHANNEL_STATE_VAR_NONE;
515     chan->remote_sig_id = L2CAP_SIG_ID_INVALID;
516     chan->local_sig_id = L2CAP_SIG_ID_INVALID;
517 
518     // add to connections list
519     linked_list_add(&l2cap_channels, (linked_item_t *) chan);
520 
521     l2cap_run();
522 }
523 
524 void l2cap_disconnect_internal(uint16_t local_cid, uint8_t reason){
525     // find channel for local_cid
526     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
527     if (channel) {
528         channel->state = L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST;
529     }
530     // process
531     l2cap_run();
532 }
533 
534 static void l2cap_handle_connection_failed_for_addr(bd_addr_t address, uint8_t status){
535     linked_item_t *it = (linked_item_t *) &l2cap_channels;
536     while (it->next){
537         l2cap_channel_t * channel = (l2cap_channel_t *) it->next;
538         if ( ! BD_ADDR_CMP( channel->address, address) ){
539             if (channel->state == L2CAP_STATE_WAIT_CONNECTION_COMPLETE || channel->state == L2CAP_STATE_WILL_SEND_CREATE_CONNECTION) {
540                 // failure, forward error code
541                 l2cap_emit_channel_opened(channel, status);
542                 // discard channel
543                 it->next = it->next->next;
544                 btstack_memory_l2cap_channel_free(channel);
545             }
546         } else {
547             it = it->next;
548         }
549     }
550 }
551 
552 static void l2cap_handle_connection_success_for_addr(bd_addr_t address, hci_con_handle_t handle){
553     linked_item_t *it;
554     for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
555         l2cap_channel_t * channel = (l2cap_channel_t *) it;
556         if ( ! BD_ADDR_CMP( channel->address, address) ){
557             if (channel->state == L2CAP_STATE_WAIT_CONNECTION_COMPLETE || channel->state == L2CAP_STATE_WILL_SEND_CREATE_CONNECTION) {
558                 // success, start l2cap handshake
559                 channel->state = L2CAP_STATE_WILL_SEND_CONNECTION_REQUEST;
560                 channel->handle = handle;
561                 channel->local_cid = l2cap_next_local_cid();
562             }
563         }
564     }
565     // process
566     l2cap_run();
567 }
568 
569 void l2cap_event_handler( uint8_t *packet, uint16_t size ){
570 
571     bd_addr_t address;
572     hci_con_handle_t handle;
573     l2cap_channel_t * channel;
574     linked_item_t *it;
575     int hci_con_used;
576 
577     switch(packet[0]){
578 
579         // handle connection complete events
580         case HCI_EVENT_CONNECTION_COMPLETE:
581             bt_flip_addr(address, &packet[5]);
582             if (packet[2] == 0){
583                 handle = READ_BT_16(packet, 3);
584                 l2cap_handle_connection_success_for_addr(address, handle);
585             } else {
586                 l2cap_handle_connection_failed_for_addr(address, packet[2]);
587             }
588             break;
589 
590         // handle successful create connection cancel command
591         case HCI_EVENT_COMMAND_COMPLETE:
592             if ( COMMAND_COMPLETE_EVENT(packet, hci_create_connection_cancel) ) {
593                 if (packet[5] == 0){
594                     bt_flip_addr(address, &packet[6]);
595                     // CONNECTION TERMINATED BY LOCAL HOST (0X16)
596                     l2cap_handle_connection_failed_for_addr(address, 0x16);
597                 }
598             }
599             l2cap_run();    // try sending signaling packets first
600             break;
601 
602         case HCI_EVENT_COMMAND_STATUS:
603             l2cap_run();    // try sending signaling packets first
604             break;
605 
606         // handle disconnection complete events
607         case HCI_EVENT_DISCONNECTION_COMPLETE:
608             // send l2cap disconnect events for all channels on this handle
609             handle = READ_BT_16(packet, 3);
610             it = (linked_item_t *) &l2cap_channels;
611             while (it->next){
612                 l2cap_channel_t * channel = (l2cap_channel_t *) it->next;
613                 if ( channel->handle == handle ){
614                     // update prev item before free'ing next element - don't call l2cap_finalize_channel_close
615                     it->next = it->next->next;
616                     l2cap_emit_channel_closed(channel);
617                     btstack_memory_l2cap_channel_free(channel);
618                 } else {
619                     it = it->next;
620                 }
621             }
622             break;
623 
624         case HCI_EVENT_NUMBER_OF_COMPLETED_PACKETS:
625             l2cap_run();    // try sending signaling packets first
626             l2cap_hand_out_credits();
627             break;
628 
629         // HCI Connection Timeouts
630         case L2CAP_EVENT_TIMEOUT_CHECK:
631             handle = READ_BT_16(packet, 2);
632             if (hci_authentication_active_for_handle(handle)) break;
633             hci_con_used = 0;
634             for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
635                 channel = (l2cap_channel_t *) it;
636                 if (channel->handle == handle) {
637                     hci_con_used = 1;
638                 }
639             }
640             if (hci_con_used) break;
641             if (!hci_can_send_packet_now(HCI_COMMAND_DATA_PACKET)) break;
642             hci_send_cmd(&hci_disconnect, handle, 0x13); // remote closed connection
643             break;
644 
645         case DAEMON_EVENT_HCI_PACKET_SENT:
646             for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
647                 channel = (l2cap_channel_t *) it;
648                 if (channel->packet_handler) {
649                     (* (channel->packet_handler))(HCI_EVENT_PACKET, channel->local_cid, packet, size);
650                 }
651             }
652             if (attribute_protocol_packet_handler) {
653                 (*attribute_protocol_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
654             }
655             if (security_protocol_packet_handler) {
656                 (*security_protocol_packet_handler)(SM_DATA_PACKET, 0, packet, size);
657             }
658             break;
659 
660         default:
661             break;
662     }
663 
664     // pass on
665     (*packet_handler)(NULL, HCI_EVENT_PACKET, 0, packet, size);
666 }
667 
668 static void l2cap_handle_disconnect_request(l2cap_channel_t *channel, uint16_t identifier){
669     channel->remote_sig_id = identifier;
670     channel->state = L2CAP_STATE_WILL_SEND_DISCONNECT_RESPONSE;
671     l2cap_run();
672 }
673 
674 static void l2cap_register_signaling_response(hci_con_handle_t handle, uint8_t code, uint8_t sig_id, uint16_t data){
675     if (signaling_responses_pending < NR_PENDING_SIGNALING_RESPONSES) {
676         signaling_responses[signaling_responses_pending].handle = handle;
677         signaling_responses[signaling_responses_pending].code = code;
678         signaling_responses[signaling_responses_pending].sig_id = sig_id;
679         signaling_responses[signaling_responses_pending].data = data;
680         signaling_responses_pending++;
681         l2cap_run();
682     }
683 }
684 
685 static void l2cap_handle_connection_request(hci_con_handle_t handle, uint8_t sig_id, uint16_t psm, uint16_t source_cid){
686 
687     // log_info("l2cap_handle_connection_request for handle %u, psm %u cid %u\n", handle, psm, source_cid);
688     l2cap_service_t *service = l2cap_get_service(psm);
689     if (!service) {
690         // 0x0002 PSM not supported
691         l2cap_register_signaling_response(handle, CONNECTION_REQUEST, sig_id, 0x0002);
692         return;
693     }
694 
695     hci_connection_t * hci_connection = connection_for_handle( handle );
696     if (!hci_connection) {
697         //
698         log_error("no hci_connection for handle %u\n", handle);
699         return;
700     }
701     // alloc structure
702     // log_info("l2cap_handle_connection_request register channel\n");
703     l2cap_channel_t * channel = (l2cap_channel_t*) btstack_memory_l2cap_channel_get();
704     if (!channel){
705         // 0x0004 No resources available
706         l2cap_register_signaling_response(handle, CONNECTION_REQUEST, sig_id, 0x0004);
707         return;
708     }
709 
710     // fill in
711     BD_ADDR_COPY(channel->address, hci_connection->address);
712     channel->psm = psm;
713     channel->handle = handle;
714     channel->connection = service->connection;
715     channel->packet_handler = service->packet_handler;
716     channel->local_cid  = l2cap_next_local_cid();
717     channel->remote_cid = source_cid;
718     channel->local_mtu  = service->mtu;
719     channel->remote_mtu = L2CAP_DEFAULT_MTU;
720     channel->packets_granted = 0;
721     channel->remote_sig_id = sig_id;
722 
723     // limit local mtu to max acl packet length
724     if (channel->local_mtu > l2cap_max_mtu()) {
725         channel->local_mtu = l2cap_max_mtu();
726     }
727 
728     // set initial state
729     channel->state = L2CAP_STATE_WAIT_CLIENT_ACCEPT_OR_REJECT;
730     channel->state_var = L2CAP_CHANNEL_STATE_VAR_NONE;
731 
732     // add to connections list
733     linked_list_add(&l2cap_channels, (linked_item_t *) channel);
734 
735     // emit incoming connection request
736     l2cap_emit_connection_request(channel);
737 }
738 
739 void l2cap_accept_connection_internal(uint16_t local_cid){
740     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
741     if (!channel) {
742         log_error("l2cap_accept_connection_internal called but local_cid 0x%x not found", local_cid);
743         return;
744     }
745 
746     channel->state = L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_ACCEPT;
747 
748     // process
749     l2cap_run();
750 }
751 
752 void l2cap_decline_connection_internal(uint16_t local_cid, uint8_t reason){
753     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid( local_cid);
754     if (!channel) {
755         log_error( "l2cap_decline_connection_internal called but local_cid 0x%x not found", local_cid);
756         return;
757     }
758     channel->state  = L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_DECLINE;
759     channel->reason = reason;
760     l2cap_run();
761 }
762 
763 void l2cap_signaling_handle_configure_request(l2cap_channel_t *channel, uint8_t *command){
764 
765     channel->remote_sig_id = command[L2CAP_SIGNALING_COMMAND_SIGID_OFFSET];
766 
767     // accept the other's configuration options
768     uint16_t end_pos = 4 + READ_BT_16(command, L2CAP_SIGNALING_COMMAND_LENGTH_OFFSET);
769     uint16_t pos     = 8;
770     while (pos < end_pos){
771         uint8_t type   = command[pos++];
772         uint8_t length = command[pos++];
773         // MTU { type(8): 1, len(8):2, MTU(16) }
774         if ((type & 0x7f) == 1 && length == 2){
775             channel->remote_mtu = READ_BT_16(command, pos);
776             // log_info("l2cap cid %u, remote mtu %u\n", channel->local_cid, channel->remote_mtu);
777         }
778         pos += length;
779     }
780 }
781 
782 static int l2cap_channel_ready_for_open(l2cap_channel_t *channel){
783     // log_info("l2cap_channel_ready_for_open 0x%02x\n", channel->state_var);
784     if ((channel->state_var & L2CAP_CHANNEL_STATE_VAR_RCVD_CONF_RSP) == 0) return 0;
785     if ((channel->state_var & L2CAP_CHANNEL_STATE_VAR_SENT_CONF_RSP) == 0) return 0;
786     return 1;
787 }
788 
789 
790 void l2cap_signaling_handler_channel(l2cap_channel_t *channel, uint8_t *command){
791 
792     uint8_t  code       = command[L2CAP_SIGNALING_COMMAND_CODE_OFFSET];
793     uint8_t  identifier = command[L2CAP_SIGNALING_COMMAND_SIGID_OFFSET];
794     uint16_t result = 0;
795 
796     log_info("L2CAP signaling handler code %u, state %u\n", code, channel->state);
797 
798     // handle DISCONNECT REQUESTS seperately
799     if (code == DISCONNECTION_REQUEST){
800         switch (channel->state){
801             case L2CAP_STATE_CONFIG:
802             case L2CAP_STATE_OPEN:
803             case L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST:
804             case L2CAP_STATE_WAIT_DISCONNECT:
805                 l2cap_handle_disconnect_request(channel, identifier);
806                 break;
807 
808             default:
809                 // ignore in other states
810                 break;
811         }
812         return;
813     }
814 
815     // @STATEMACHINE(l2cap)
816     switch (channel->state) {
817 
818         case L2CAP_STATE_WAIT_CONNECT_RSP:
819             switch (code){
820                 case CONNECTION_RESPONSE:
821                     result = READ_BT_16 (command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET+4);
822                     switch (result) {
823                         case 0:
824                             // successful connection
825                             channel->remote_cid = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
826                             channel->state = L2CAP_STATE_CONFIG;
827                             channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
828                             break;
829                         case 1:
830                             // connection pending. get some coffee
831                             break;
832                         default:
833                             // channel closed
834                             channel->state = L2CAP_STATE_CLOSED;
835 
836                             // map l2cap connection response result to BTstack status enumeration
837                             l2cap_emit_channel_opened(channel, L2CAP_CONNECTION_RESPONSE_RESULT_SUCCESSFUL + result);
838 
839                             // drop link key if security block
840                             if (L2CAP_CONNECTION_RESPONSE_RESULT_SUCCESSFUL + result == L2CAP_CONNECTION_RESPONSE_RESULT_REFUSED_SECURITY){
841                                 hci_drop_link_key_for_bd_addr(&channel->address);
842                             }
843 
844                             // discard channel
845                             linked_list_remove(&l2cap_channels, (linked_item_t *) channel);
846                             btstack_memory_l2cap_channel_free(channel);
847                             break;
848                     }
849                     break;
850 
851                 default:
852                     //@TODO: implement other signaling packets
853                     break;
854             }
855             break;
856 
857         case L2CAP_STATE_CONFIG:
858             switch (code) {
859                 case CONFIGURE_REQUEST:
860                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_RCVD_CONF_REQ);
861                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP);
862                     l2cap_signaling_handle_configure_request(channel, command);
863                     break;
864                 case CONFIGURE_RESPONSE:
865                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_RCVD_CONF_RSP);
866                     break;
867                 default:
868                     break;
869             }
870             if (l2cap_channel_ready_for_open(channel)){
871                 // for open:
872                 channel->state = L2CAP_STATE_OPEN;
873                 l2cap_emit_channel_opened(channel, 0);
874                 l2cap_emit_credits(channel, 1);
875             }
876             break;
877 
878         case L2CAP_STATE_WAIT_DISCONNECT:
879             switch (code) {
880                 case DISCONNECTION_RESPONSE:
881                     l2cap_finialize_channel_close(channel);
882                     break;
883                 default:
884                     //@TODO: implement other signaling packets
885                     break;
886             }
887             break;
888 
889         case L2CAP_STATE_CLOSED:
890             // @TODO handle incoming requests
891             break;
892 
893         case L2CAP_STATE_OPEN:
894             //@TODO: implement other signaling packets, e.g. re-configure
895             break;
896         default:
897             break;
898     }
899     // log_info("new state %u\n", channel->state);
900 }
901 
902 
903 void l2cap_signaling_handler_dispatch( hci_con_handle_t handle, uint8_t * command){
904 
905     // get code, signalind identifier and command len
906     uint8_t code   = command[L2CAP_SIGNALING_COMMAND_CODE_OFFSET];
907     uint8_t sig_id = command[L2CAP_SIGNALING_COMMAND_SIGID_OFFSET];
908 
909     // not for a particular channel, and not CONNECTION_REQUEST, ECHO_[REQUEST|RESPONSE], INFORMATION_REQUEST
910     if (code < 1 || code == ECHO_RESPONSE || code > INFORMATION_REQUEST){
911         return;
912     }
913 
914     // general commands without an assigned channel
915     switch(code) {
916 
917         case CONNECTION_REQUEST: {
918             uint16_t psm =        READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
919             uint16_t source_cid = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET+2);
920             l2cap_handle_connection_request(handle, sig_id, psm, source_cid);
921             return;
922         }
923 
924         case ECHO_REQUEST:
925             l2cap_register_signaling_response(handle, code, sig_id, 0);
926             return;
927 
928         case INFORMATION_REQUEST: {
929             uint16_t infoType = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
930             l2cap_register_signaling_response(handle, code, sig_id, infoType);
931             return;
932         }
933 
934         default:
935             break;
936     }
937 
938 
939     // Get potential destination CID
940     uint16_t dest_cid = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
941 
942     // Find channel for this sig_id and connection handle
943     linked_item_t *it;
944     for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
945         l2cap_channel_t * channel = (l2cap_channel_t *) it;
946         if (channel->handle == handle) {
947             if (code & 1) {
948                 // match odd commands (responses) by previous signaling identifier
949                 if (channel->local_sig_id == sig_id) {
950                     l2cap_signaling_handler_channel(channel, command);
951                     break;
952                 }
953             } else {
954                 // match even commands (requests) by local channel id
955                 if (channel->local_cid == dest_cid) {
956                     l2cap_signaling_handler_channel(channel, command);
957                     break;
958                 }
959             }
960         }
961     }
962 }
963 
964 void l2cap_acl_handler( uint8_t *packet, uint16_t size ){
965 
966     // Get Channel ID
967     uint16_t channel_id = READ_L2CAP_CHANNEL_ID(packet);
968     hci_con_handle_t handle = READ_ACL_CONNECTION_HANDLE(packet);
969 
970     switch (channel_id) {
971 
972         case L2CAP_CID_SIGNALING: {
973 
974             uint16_t command_offset = 8;
975             while (command_offset < size) {
976 
977                 // handle signaling commands
978                 l2cap_signaling_handler_dispatch(handle, &packet[command_offset]);
979 
980                 // increment command_offset
981                 command_offset += L2CAP_SIGNALING_COMMAND_DATA_OFFSET + READ_BT_16(packet, command_offset + L2CAP_SIGNALING_COMMAND_LENGTH_OFFSET);
982             }
983             break;
984         }
985 
986         case L2CAP_CID_ATTRIBUTE_PROTOCOL:
987             if (attribute_protocol_packet_handler) {
988                 (*attribute_protocol_packet_handler)(ATT_DATA_PACKET, handle, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
989             }
990             break;
991 
992         case L2CAP_CID_SECURITY_MANAGER_PROTOCOL:
993             if (security_protocol_packet_handler) {
994                 (*security_protocol_packet_handler)(SM_DATA_PACKET, handle, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
995             }
996             break;
997 
998         default: {
999             // Find channel for this channel_id and connection handle
1000             l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(channel_id);
1001             if (channel) {
1002                 l2cap_dispatch(channel, L2CAP_DATA_PACKET, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
1003             }
1004             break;
1005         }
1006     }
1007 
1008     l2cap_run();
1009 }
1010 
1011 static void l2cap_packet_handler(uint8_t packet_type, uint8_t *packet, uint16_t size){
1012     switch (packet_type) {
1013         case HCI_EVENT_PACKET:
1014             l2cap_event_handler(packet, size);
1015             break;
1016         case HCI_ACL_DATA_PACKET:
1017             l2cap_acl_handler(packet, size);
1018             break;
1019         default:
1020             break;
1021     }
1022 }
1023 
1024 // finalize closed channel - l2cap_handle_disconnect_request & DISCONNECTION_RESPONSE
1025 void l2cap_finialize_channel_close(l2cap_channel_t *channel){
1026     channel->state = L2CAP_STATE_CLOSED;
1027     l2cap_emit_channel_closed(channel);
1028     // discard channel
1029     linked_list_remove(&l2cap_channels, (linked_item_t *) channel);
1030     btstack_memory_l2cap_channel_free(channel);
1031 }
1032 
1033 l2cap_service_t * l2cap_get_service(uint16_t psm){
1034     linked_item_t *it;
1035 
1036     // close open channels
1037     for (it = (linked_item_t *) l2cap_services; it ; it = it->next){
1038         l2cap_service_t * service = ((l2cap_service_t *) it);
1039         if ( service->psm == psm){
1040             return service;
1041         };
1042     }
1043     return NULL;
1044 }
1045 
1046 void l2cap_register_service_internal(void *connection, btstack_packet_handler_t packet_handler, uint16_t psm, uint16_t mtu){
1047     // check for alread registered psm
1048     // TODO: emit error event
1049     l2cap_service_t *service = l2cap_get_service(psm);
1050     if (service) {
1051         log_error("l2cap_register_service_internal: PSM %u already registered\n", psm);
1052         l2cap_emit_service_registered(connection, L2CAP_SERVICE_ALREADY_REGISTERED, psm);
1053         return;
1054     }
1055 
1056     // alloc structure
1057     // TODO: emit error event
1058     service = (l2cap_service_t *) btstack_memory_l2cap_service_get();
1059     if (!service) {
1060         log_error("l2cap_register_service_internal: no memory for l2cap_service_t\n");
1061         l2cap_emit_service_registered(connection, BTSTACK_MEMORY_ALLOC_FAILED, psm);
1062         return;
1063     }
1064 
1065     // fill in
1066     service->psm = psm;
1067     service->mtu = mtu;
1068     service->connection = connection;
1069     service->packet_handler = packet_handler;
1070 
1071     // add to services list
1072     linked_list_add(&l2cap_services, (linked_item_t *) service);
1073 
1074     // enable page scan
1075     hci_connectable_control(1);
1076 
1077     // done
1078     l2cap_emit_service_registered(connection, 0, psm);
1079 }
1080 
1081 void l2cap_unregister_service_internal(void *connection, uint16_t psm){
1082     l2cap_service_t *service = l2cap_get_service(psm);
1083     if (!service) return;
1084     linked_list_remove(&l2cap_services, (linked_item_t *) service);
1085     btstack_memory_l2cap_service_free(service);
1086 
1087     // disable page scan when no services registered
1088     if (!linked_list_empty(&l2cap_services)) return;
1089     hci_connectable_control(0);
1090 }
1091 
1092 //
1093 void l2cap_close_connection(void *connection){
1094     linked_item_t *it;
1095 
1096     // close open channels - note to myself: no channel is freed, so no new for fancy iterator tricks
1097     l2cap_channel_t * channel;
1098     for (it = (linked_item_t *) l2cap_channels; it ; it = it->next){
1099         channel = (l2cap_channel_t *) it;
1100         if (channel->connection == connection) {
1101             channel->state = L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST;
1102         }
1103     }
1104 
1105     // unregister services
1106     it = (linked_item_t *) &l2cap_services;
1107     while (it->next) {
1108         l2cap_service_t * service = (l2cap_service_t *) it->next;
1109         if (service->connection == connection){
1110             it->next = it->next->next;
1111             btstack_memory_l2cap_service_free(service);
1112         } else {
1113             it = it->next;
1114         }
1115     }
1116 
1117     // process
1118     l2cap_run();
1119 }
1120 
1121 // Bluetooth 4.0 - allows to register handler for Attribute Protocol and Security Manager Protocol
1122 void l2cap_register_fixed_channel(btstack_packet_handler_t packet_handler, uint16_t channel_id) {
1123     switch(channel_id){
1124         case L2CAP_CID_ATTRIBUTE_PROTOCOL:
1125             attribute_protocol_packet_handler = packet_handler;
1126             break;
1127         case L2CAP_CID_SECURITY_MANAGER_PROTOCOL:
1128             security_protocol_packet_handler = packet_handler;
1129             break;
1130     }
1131 }
1132 
1133