xref: /btstack/src/l2cap.c (revision 2e77e513be6c9b9bbf66ef944e189d0f5074daad)
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
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33  * Please inquire about commercial licensing options at
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36  */
37 
38 /*
39  *  l2cap.c
40  *
41  *  Logical Link Control and Adaption Protocl (L2CAP)
42  *
43  *  Created by Matthias Ringwald on 5/16/09.
44  */
45 
46 #include "l2cap.h"
47 #include "hci.h"
48 #include "hci_dump.h"
49 #include "debug.h"
50 #include "btstack_memory.h"
51 
52 #include <stdarg.h>
53 #include <string.h>
54 
55 #include <stdio.h>
56 
57 // nr of buffered acl packets in outgoing queue to get max performance
58 #define NR_BUFFERED_ACL_PACKETS 3
59 
60 // used to cache l2cap rejects, echo, and informational requests
61 #define NR_PENDING_SIGNALING_RESPONSES 3
62 
63 // offsets for L2CAP SIGNALING COMMANDS
64 #define L2CAP_SIGNALING_COMMAND_CODE_OFFSET   0
65 #define L2CAP_SIGNALING_COMMAND_SIGID_OFFSET  1
66 #define L2CAP_SIGNALING_COMMAND_LENGTH_OFFSET 2
67 #define L2CAP_SIGNALING_COMMAND_DATA_OFFSET   4
68 
69 static void null_packet_handler(void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size);
70 static void l2cap_packet_handler(uint8_t packet_type, uint8_t *packet, uint16_t size);
71 
72 // used to cache l2cap rejects, echo, and informational requests
73 static l2cap_signaling_response_t signaling_responses[NR_PENDING_SIGNALING_RESPONSES];
74 static int signaling_responses_pending;
75 
76 static linked_list_t l2cap_channels;
77 static linked_list_t l2cap_services;
78 static void (*packet_handler) (void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size) = null_packet_handler;
79 static int new_credits_blocked = 0;
80 
81 static btstack_packet_handler_t attribute_protocol_packet_handler;
82 static btstack_packet_handler_t security_protocol_packet_handler;
83 static btstack_packet_handler_t connectionless_channel_packet_handler;
84 static uint8_t require_security_level2_for_outgoing_sdp;
85 
86 // prototypes
87 static void l2cap_finialize_channel_close(l2cap_channel_t *channel);
88 static l2cap_service_t * l2cap_get_service(uint16_t psm);
89 static void l2cap_emit_channel_opened(l2cap_channel_t *channel, uint8_t status);
90 static void l2cap_emit_channel_closed(l2cap_channel_t *channel);
91 static void l2cap_emit_connection_request(l2cap_channel_t *channel);
92 static int l2cap_channel_ready_for_open(l2cap_channel_t *channel);
93 
94 
95 void l2cap_init(){
96     new_credits_blocked = 0;
97     signaling_responses_pending = 0;
98 
99     l2cap_channels = NULL;
100     l2cap_services = NULL;
101 
102     packet_handler = null_packet_handler;
103     attribute_protocol_packet_handler = NULL;
104     security_protocol_packet_handler = NULL;
105     connectionless_channel_packet_handler = NULL;
106 
107     require_security_level2_for_outgoing_sdp = 0;
108 
109     //
110     // register callback with HCI
111     //
112     hci_register_packet_handler(&l2cap_packet_handler);
113     hci_connectable_control(0); // no services yet
114 }
115 
116 
117 /** Register L2CAP packet handlers */
118 static void null_packet_handler(void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
119 }
120 void l2cap_register_packet_handler(void (*handler)(void * connection, uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size)){
121     packet_handler = handler;
122 }
123 
124 //  notify client/protocol handler
125 void l2cap_dispatch(l2cap_channel_t *channel, uint8_t type, uint8_t * data, uint16_t size){
126     if (channel->packet_handler) {
127         (* (channel->packet_handler))(type, channel->local_cid, data, size);
128     } else {
129         (*packet_handler)(channel->connection, type, channel->local_cid, data, size);
130     }
131 }
132 
133 void l2cap_emit_channel_opened(l2cap_channel_t *channel, uint8_t status) {
134     log_info("L2CAP_EVENT_CHANNEL_OPENED status 0x%x addr %s handle 0x%x psm 0x%x local_cid 0x%x remote_cid 0x%x local_mtu %u, remote_mtu %u, flush_timeout %u",
135              status, bd_addr_to_str(channel->address), channel->handle, channel->psm,
136              channel->local_cid, channel->remote_cid, channel->local_mtu, channel->remote_mtu, channel->flush_timeout);
137     uint8_t event[23];
138     event[0] = L2CAP_EVENT_CHANNEL_OPENED;
139     event[1] = sizeof(event) - 2;
140     event[2] = status;
141     bt_flip_addr(&event[3], channel->address);
142     bt_store_16(event,  9, channel->handle);
143     bt_store_16(event, 11, channel->psm);
144     bt_store_16(event, 13, channel->local_cid);
145     bt_store_16(event, 15, channel->remote_cid);
146     bt_store_16(event, 17, channel->local_mtu);
147     bt_store_16(event, 19, channel->remote_mtu);
148     bt_store_16(event, 21, channel->flush_timeout);
149     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
150     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
151 }
152 
153 void l2cap_emit_channel_closed(l2cap_channel_t *channel) {
154     log_info("L2CAP_EVENT_CHANNEL_CLOSED local_cid 0x%x", channel->local_cid);
155     uint8_t event[4];
156     event[0] = L2CAP_EVENT_CHANNEL_CLOSED;
157     event[1] = sizeof(event) - 2;
158     bt_store_16(event, 2, channel->local_cid);
159     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
160     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
161 }
162 
163 void l2cap_emit_connection_request(l2cap_channel_t *channel) {
164     log_info("L2CAP_EVENT_INCOMING_CONNECTION addr %s handle 0x%x psm 0x%x local_cid 0x%x remote_cid 0x%x",
165              bd_addr_to_str(channel->address), channel->handle,  channel->psm, channel->local_cid, channel->remote_cid);
166     uint8_t event[16];
167     event[0] = L2CAP_EVENT_INCOMING_CONNECTION;
168     event[1] = sizeof(event) - 2;
169     bt_flip_addr(&event[2], channel->address);
170     bt_store_16(event,  8, channel->handle);
171     bt_store_16(event, 10, channel->psm);
172     bt_store_16(event, 12, channel->local_cid);
173     bt_store_16(event, 14, channel->remote_cid);
174     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
175     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
176 }
177 
178 void l2cap_emit_connection_parameter_update_response(uint16_t handle, uint16_t result){
179     uint8_t event[6];
180     event[0] = L2CAP_EVENT_CONNECTION_PARAMETER_UPDATE_RESPONSE;
181     event[1] = 4;
182     bt_store_16(event, 2, handle);
183     bt_store_16(event, 4, result);
184     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
185     (*packet_handler)(NULL, HCI_EVENT_PACKET, 0, event, sizeof(event));
186 }
187 
188 static void l2cap_emit_service_registered(void *connection, uint8_t status, uint16_t psm){
189     log_info("L2CAP_EVENT_SERVICE_REGISTERED status 0x%x psm 0x%x", status, psm);
190     uint8_t event[5];
191     event[0] = L2CAP_EVENT_SERVICE_REGISTERED;
192     event[1] = sizeof(event) - 2;
193     event[2] = status;
194     bt_store_16(event, 3, psm);
195     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
196     (*packet_handler)(connection, HCI_EVENT_PACKET, 0, event, sizeof(event));
197 }
198 
199 void l2cap_emit_credits(l2cap_channel_t *channel, uint8_t credits) {
200 
201     log_info("L2CAP_EVENT_CREDITS local_cid 0x%x credits %u", channel->local_cid, credits);
202     // track credits
203     channel->packets_granted += credits;
204 
205     uint8_t event[5];
206     event[0] = L2CAP_EVENT_CREDITS;
207     event[1] = sizeof(event) - 2;
208     bt_store_16(event, 2, channel->local_cid);
209     event[4] = credits;
210     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
211     l2cap_dispatch(channel, HCI_EVENT_PACKET, event, sizeof(event));
212 }
213 
214 void l2cap_block_new_credits(uint8_t blocked){
215     new_credits_blocked = blocked;
216 }
217 
218 void l2cap_hand_out_credits(void){
219 
220     if (new_credits_blocked) return;    // we're told not to. used by daemon
221 
222     linked_list_iterator_t it;
223     linked_list_iterator_init(&it, &l2cap_channels);
224     while (linked_list_iterator_has_next(&it)){
225         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
226         if (!hci_number_free_acl_slots_for_handle(channel->handle)) return;
227         if (channel->state != L2CAP_STATE_OPEN) continue;
228         if (hci_number_outgoing_packets(channel->handle) < NR_BUFFERED_ACL_PACKETS && channel->packets_granted == 0) {
229             l2cap_emit_credits(channel, 1);
230         }
231     }
232 }
233 
234 l2cap_channel_t * l2cap_get_channel_for_local_cid(uint16_t local_cid){
235     linked_list_iterator_t it;
236     linked_list_iterator_init(&it, &l2cap_channels);
237     while (linked_list_iterator_has_next(&it)){
238         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
239         if ( channel->local_cid == local_cid) {
240             return channel;
241         }
242     }
243     return NULL;
244 }
245 
246 int  l2cap_can_send_packet_now(uint16_t local_cid){
247     l2cap_channel_t *channel = l2cap_get_channel_for_local_cid(local_cid);
248     if (!channel) return 0;
249     if (!channel->packets_granted) return 0;
250     return hci_can_send_acl_packet_now(channel->handle);
251 }
252 
253 // @deprecated
254 int l2cap_can_send_connectionless_packet_now(void){
255     // TODO provide real handle
256     return l2cap_can_send_fixed_channel_packet_now(0x1234);
257 }
258 
259 int  l2cap_can_send_fixed_channel_packet_now(uint16_t handle){
260     return hci_can_send_acl_packet_now(handle);
261 }
262 
263 uint16_t l2cap_get_remote_mtu_for_local_cid(uint16_t local_cid){
264     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
265     if (channel) {
266         return channel->remote_mtu;
267     }
268     return 0;
269 }
270 
271 static l2cap_channel_t * l2cap_channel_for_rtx_timer(timer_source_t * ts){
272     linked_list_iterator_t it;
273     linked_list_iterator_init(&it, &l2cap_channels);
274     while (linked_list_iterator_has_next(&it)){
275         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
276         if ( &channel->rtx == ts) {
277             return channel;
278         }
279     }
280     return NULL;
281 }
282 
283 static void l2cap_rtx_timeout(timer_source_t * ts){
284     l2cap_channel_t * channel = l2cap_channel_for_rtx_timer(ts);
285     if (!ts) return;
286 
287     log_info("l2cap_rtx_timeout for local cid 0x%02x", channel->local_cid);
288 
289     // "When terminating the channel, it is not necessary to send a L2CAP_DisconnectReq
290     //  and enter WAIT_DISCONNECT state. Channels can be transitioned directly to the CLOSED state."
291     // notify client
292     l2cap_emit_channel_opened(channel, L2CAP_CONNECTION_RESPONSE_RESULT_RTX_TIMEOUT);
293 
294     // discard channel
295     // no need to stop timer here, it is removed from list during timer callback
296     linked_list_remove(&l2cap_channels, (linked_item_t *) channel);
297     btstack_memory_l2cap_channel_free(channel);
298 }
299 
300 static void l2cap_stop_rtx(l2cap_channel_t * channel){
301     log_info("l2cap_stop_rtx for local cid 0x%02x", channel->local_cid);
302     run_loop_remove_timer(&channel->rtx);
303 }
304 
305 static void l2cap_start_rtx(l2cap_channel_t * channel){
306     l2cap_stop_rtx(channel);
307     log_info("l2cap_start_rtx for local cid 0x%02x", channel->local_cid);
308     run_loop_set_timer_handler(&channel->rtx, l2cap_rtx_timeout);
309     run_loop_set_timer(&channel->rtx, L2CAP_RTX_TIMEOUT_MS);
310     run_loop_add_timer(&channel->rtx);
311 }
312 
313 static void l2cap_start_ertx(l2cap_channel_t * channel){
314     log_info("l2cap_start_ertx for local cid 0x%02x", channel->local_cid);
315     l2cap_stop_rtx(channel);
316     run_loop_set_timer_handler(&channel->rtx, l2cap_rtx_timeout);
317     run_loop_set_timer(&channel->rtx, L2CAP_ERTX_TIMEOUT_MS);
318     run_loop_add_timer(&channel->rtx);
319 }
320 
321 void l2cap_require_security_level_2_for_outgoing_sdp(){
322     require_security_level2_for_outgoing_sdp = 1;
323 }
324 
325 static int l2cap_security_level_0_allowed_for_PSM(uint16_t psm){
326     return (psm == PSM_SDP) && (!require_security_level2_for_outgoing_sdp);
327 }
328 
329 int l2cap_send_signaling_packet(hci_con_handle_t handle, L2CAP_SIGNALING_COMMANDS cmd, uint8_t identifier, ...){
330 
331     if (!hci_can_send_acl_packet_now(handle)){
332         log_info("l2cap_send_signaling_packet, cannot send");
333         return BTSTACK_ACL_BUFFERS_FULL;
334     }
335 
336     // log_info("l2cap_send_signaling_packet type %u", cmd);
337     hci_reserve_packet_buffer();
338     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
339     va_list argptr;
340     va_start(argptr, identifier);
341     uint16_t len = l2cap_create_signaling_classic(acl_buffer, handle, cmd, identifier, argptr);
342     va_end(argptr);
343     // log_info("l2cap_send_signaling_packet con %u!", handle);
344     return hci_send_acl_packet_buffer(len);
345 }
346 
347 #ifdef HAVE_BLE
348 int l2cap_send_le_signaling_packet(hci_con_handle_t handle, L2CAP_SIGNALING_COMMANDS cmd, uint8_t identifier, ...){
349 
350     if (!hci_can_send_acl_packet_now(handle)){
351         log_info("l2cap_send_signaling_packet, cannot send");
352         return BTSTACK_ACL_BUFFERS_FULL;
353     }
354 
355     // log_info("l2cap_send_signaling_packet type %u", cmd);
356     hci_reserve_packet_buffer();
357     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
358     va_list argptr;
359     va_start(argptr, identifier);
360     uint16_t len = l2cap_create_signaling_le(acl_buffer, handle, cmd, identifier, argptr);
361     va_end(argptr);
362     // log_info("l2cap_send_signaling_packet con %u!", handle);
363     return hci_send_acl_packet_buffer(len);
364 }
365 #endif
366 
367 uint8_t *l2cap_get_outgoing_buffer(void){
368     return hci_get_outgoing_packet_buffer() + COMPLETE_L2CAP_HEADER; // 8 bytes
369 }
370 
371 int l2cap_reserve_packet_buffer(void){
372     return hci_reserve_packet_buffer();
373 }
374 
375 void l2cap_release_packet_buffer(void){
376     hci_release_packet_buffer();
377 }
378 
379 
380 int l2cap_send_prepared(uint16_t local_cid, uint16_t len){
381 
382     if (!hci_is_packet_buffer_reserved()){
383         log_error("l2cap_send_prepared called without reserving packet first");
384         return BTSTACK_ACL_BUFFERS_FULL;
385     }
386 
387     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
388     if (!channel) {
389         log_error("l2cap_send_prepared no channel for cid 0x%02x", local_cid);
390         return -1;   // TODO: define error
391     }
392 
393     if (channel->packets_granted == 0){
394         log_error("l2cap_send_prepared cid 0x%02x, no credits!", local_cid);
395         return -1;  // TODO: define error
396     }
397 
398     if (!hci_can_send_prepared_acl_packet_now(channel->handle)){
399         log_info("l2cap_send_prepared cid 0x%02x, cannot send", local_cid);
400         return BTSTACK_ACL_BUFFERS_FULL;
401     }
402 
403     --channel->packets_granted;
404 
405     log_debug("l2cap_send_prepared cid 0x%02x, handle %u, 1 credit used, credits left %u;",
406                   local_cid, channel->handle, channel->packets_granted);
407 
408     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
409 
410     int pb = hci_non_flushable_packet_boundary_flag_supported() ? 0x00 : 0x02;
411 
412     // 0 - Connection handle : PB=pb : BC=00
413     bt_store_16(acl_buffer, 0, channel->handle | (pb << 12) | (0 << 14));
414     // 2 - ACL length
415     bt_store_16(acl_buffer, 2,  len + 4);
416     // 4 - L2CAP packet length
417     bt_store_16(acl_buffer, 4,  len + 0);
418     // 6 - L2CAP channel DEST
419     bt_store_16(acl_buffer, 6, channel->remote_cid);
420     // send
421     int err = hci_send_acl_packet_buffer(len+8);
422 
423     l2cap_hand_out_credits();
424 
425     return err;
426 }
427 
428 int l2cap_send_prepared_connectionless(uint16_t handle, uint16_t cid, uint16_t len){
429 
430     if (!hci_is_packet_buffer_reserved()){
431         log_error("l2cap_send_prepared_connectionless called without reserving packet first");
432         return BTSTACK_ACL_BUFFERS_FULL;
433     }
434 
435     if (!hci_can_send_prepared_acl_packet_now(handle)){
436         log_info("l2cap_send_prepared_connectionless handle 0x%02x, cid 0x%02x, cannot send", handle, cid);
437         return BTSTACK_ACL_BUFFERS_FULL;
438     }
439 
440     log_debug("l2cap_send_prepared_connectionless handle %u, cid 0x%02x", handle, cid);
441 
442     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
443 
444     int pb = hci_non_flushable_packet_boundary_flag_supported() ? 0x00 : 0x02;
445 
446     // 0 - Connection handle : PB=pb : BC=00
447     bt_store_16(acl_buffer, 0, handle | (pb << 12) | (0 << 14));
448     // 2 - ACL length
449     bt_store_16(acl_buffer, 2,  len + 4);
450     // 4 - L2CAP packet length
451     bt_store_16(acl_buffer, 4,  len + 0);
452     // 6 - L2CAP channel DEST
453     bt_store_16(acl_buffer, 6, cid);
454     // send
455     int err = hci_send_acl_packet_buffer(len+8);
456 
457     l2cap_hand_out_credits();
458 
459     return err;
460 }
461 
462 int l2cap_send_internal(uint16_t local_cid, uint8_t *data, uint16_t len){
463 
464     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
465     if (!channel) {
466         log_error("l2cap_send_internal no channel for cid 0x%02x", local_cid);
467         return -1;   // TODO: define error
468     }
469 
470     if (len > channel->remote_mtu){
471         log_error("l2cap_send_internal cid 0x%02x, data length exceeds remote MTU.", local_cid);
472         return L2CAP_DATA_LEN_EXCEEDS_REMOTE_MTU;
473     }
474 
475     if (!hci_can_send_acl_packet_now(channel->handle)){
476         log_info("l2cap_send_internal cid 0x%02x, cannot send", local_cid);
477         return BTSTACK_ACL_BUFFERS_FULL;
478     }
479 
480     hci_reserve_packet_buffer();
481     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
482 
483     memcpy(&acl_buffer[8], data, len);
484 
485     return l2cap_send_prepared(local_cid, len);
486 }
487 
488 int l2cap_send_connectionless(uint16_t handle, uint16_t cid, uint8_t *data, uint16_t len){
489 
490     if (!hci_can_send_acl_packet_now(handle)){
491         log_info("l2cap_send_internal cid 0x%02x, cannot send", cid);
492         return BTSTACK_ACL_BUFFERS_FULL;
493     }
494 
495     hci_reserve_packet_buffer();
496     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
497 
498     memcpy(&acl_buffer[8], data, len);
499 
500     return l2cap_send_prepared_connectionless(handle, cid, len);
501 }
502 
503 int l2cap_send_echo_request(uint16_t handle, uint8_t *data, uint16_t len){
504     return l2cap_send_signaling_packet(handle, ECHO_REQUEST, 0x77, len, data);
505 }
506 
507 static inline void channelStateVarSetFlag(l2cap_channel_t *channel, L2CAP_CHANNEL_STATE_VAR flag){
508     channel->state_var = (L2CAP_CHANNEL_STATE_VAR) (channel->state_var | flag);
509 }
510 
511 static inline void channelStateVarClearFlag(l2cap_channel_t *channel, L2CAP_CHANNEL_STATE_VAR flag){
512     channel->state_var = (L2CAP_CHANNEL_STATE_VAR) (channel->state_var & ~flag);
513 }
514 
515 
516 
517 // MARK: L2CAP_RUN
518 // process outstanding signaling tasks
519 void l2cap_run(void){
520 
521     // check pending signaling responses
522     while (signaling_responses_pending){
523 
524         hci_con_handle_t handle = signaling_responses[0].handle;
525 
526         if (!hci_can_send_acl_packet_now(handle)) break;
527 
528         uint8_t  sig_id = signaling_responses[0].sig_id;
529         uint16_t infoType = signaling_responses[0].data;    // INFORMATION_REQUEST
530         uint16_t result   = signaling_responses[0].data;    // CONNECTION_REQUEST, COMMAND_REJECT
531         uint8_t  response_code = signaling_responses[0].code;
532 
533         // remove first item before sending (to avoid sending response mutliple times)
534         signaling_responses_pending--;
535         int i;
536         for (i=0; i < signaling_responses_pending; i++){
537             memcpy(&signaling_responses[i], &signaling_responses[i+1], sizeof(l2cap_signaling_response_t));
538         }
539 
540         switch (response_code){
541             case CONNECTION_REQUEST:
542                 l2cap_send_signaling_packet(handle, CONNECTION_RESPONSE, sig_id, 0, 0, result, 0);
543                 // also disconnect if result is 0x0003 - security blocked
544                 if (result == 0x0003){
545                     hci_disconnect_security_block(handle);
546                 }
547                 break;
548             case ECHO_REQUEST:
549                 l2cap_send_signaling_packet(handle, ECHO_RESPONSE, sig_id, 0, NULL);
550                 break;
551             case INFORMATION_REQUEST:
552                 switch (infoType){
553                     case 1: { // Connectionless MTU
554                         uint16_t connectionless_mtu = hci_max_acl_data_packet_length();
555                         l2cap_send_signaling_packet(handle, INFORMATION_RESPONSE, sig_id, infoType, 0, sizeof(connectionless_mtu), &connectionless_mtu);
556                         break;
557                     }
558                     case 2: { // Extended Features Supported
559                         // extended features request supported, features: fixed channels, unicast connectionless data reception
560                         uint32_t features = 0x280;
561                         l2cap_send_signaling_packet(handle, INFORMATION_RESPONSE, sig_id, infoType, 0, sizeof(features), &features);
562                         break;
563                     }
564                     case 3: { // Fixed Channels Supported
565                         uint8_t map[8];
566                         memset(map, 0, 8);
567                         map[0] = 0x01;  // L2CAP Signaling Channel (0x01) + Connectionless reception (0x02)
568                         l2cap_send_signaling_packet(handle, INFORMATION_RESPONSE, sig_id, infoType, 0, sizeof(map), &map);
569                         break;
570                     }
571                     default:
572                         // all other types are not supported
573                         l2cap_send_signaling_packet(handle, INFORMATION_RESPONSE, sig_id, infoType, 1, 0, NULL);
574                         break;
575                 }
576                 break;
577             case COMMAND_REJECT:
578                 l2cap_send_signaling_packet(handle, COMMAND_REJECT, sig_id, result, 0, NULL);
579 #ifdef HAVE_BLE
580             case COMMAND_REJECT_LE:
581                 l2cap_send_le_signaling_packet(handle, COMMAND_REJECT, sig_id, result, 0, NULL);
582                 break;
583 #endif
584             default:
585                 // should not happen
586                 break;
587         }
588     }
589 
590     uint8_t  config_options[4];
591     linked_list_iterator_t it;
592     linked_list_iterator_init(&it, &l2cap_channels);
593     while (linked_list_iterator_has_next(&it)){
594 
595         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
596         // log_info("l2cap_run: state %u, var 0x%02x", channel->state, channel->state_var);
597         switch (channel->state){
598 
599             case L2CAP_STATE_WAIT_INCOMING_SECURITY_LEVEL_UPDATE:
600             case L2CAP_STATE_WAIT_CLIENT_ACCEPT_OR_REJECT:
601                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
602                 if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONN_RESP_PEND) {
603                     channelStateVarClearFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONN_RESP_PEND);
604                     l2cap_send_signaling_packet(channel->handle, CONNECTION_RESPONSE, channel->remote_sig_id, channel->local_cid, channel->remote_cid, 1, 0);
605                 }
606                 break;
607 
608             case L2CAP_STATE_WILL_SEND_CREATE_CONNECTION:
609                 if (!hci_can_send_command_packet_now()) break;
610                 // send connection request - set state first
611                 channel->state = L2CAP_STATE_WAIT_CONNECTION_COMPLETE;
612                 // BD_ADDR, Packet_Type, Page_Scan_Repetition_Mode, Reserved, Clock_Offset, Allow_Role_Switch
613                 hci_send_cmd(&hci_create_connection, channel->address, hci_usable_acl_packet_types(), 0, 0, 0, 1);
614                 break;
615 
616             case L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_DECLINE:
617                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
618                 l2cap_send_signaling_packet(channel->handle, CONNECTION_RESPONSE, channel->remote_sig_id, channel->local_cid, channel->remote_cid, channel->reason, 0);
619                 // discard channel - l2cap_finialize_channel_close without sending l2cap close event
620                 l2cap_stop_rtx(channel);
621                 linked_list_iterator_remove(&it);
622                 btstack_memory_l2cap_channel_free(channel);
623                 break;
624 
625             case L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_ACCEPT:
626                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
627                 channel->state = L2CAP_STATE_CONFIG;
628                 channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
629                 l2cap_send_signaling_packet(channel->handle, CONNECTION_RESPONSE, channel->remote_sig_id, channel->local_cid, channel->remote_cid, 0, 0);
630                 break;
631 
632             case L2CAP_STATE_WILL_SEND_CONNECTION_REQUEST:
633                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
634                 // success, start l2cap handshake
635                 channel->local_sig_id = l2cap_next_sig_id();
636                 channel->state = L2CAP_STATE_WAIT_CONNECT_RSP;
637                 l2cap_send_signaling_packet( channel->handle, CONNECTION_REQUEST, channel->local_sig_id, channel->psm, channel->local_cid);
638                 l2cap_start_rtx(channel);
639                 break;
640 
641             case L2CAP_STATE_CONFIG:
642                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
643                 if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP){
644                     uint16_t flags = 0;
645                     channelStateVarClearFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP);
646                     if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_CONT) {
647                         flags = 1;
648                     } else {
649                         channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SENT_CONF_RSP);
650                     }
651                     if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_INVALID){
652                         l2cap_send_signaling_packet(channel->handle, CONFIGURE_RESPONSE, channel->remote_sig_id, channel->remote_cid, flags, L2CAP_CONF_RESULT_UNKNOWN_OPTIONS, 0, NULL);
653                     } else if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_MTU){
654                         config_options[0] = 1; // MTU
655                         config_options[1] = 2; // len param
656                         bt_store_16( (uint8_t*)&config_options, 2, channel->remote_mtu);
657                         l2cap_send_signaling_packet(channel->handle, CONFIGURE_RESPONSE, channel->remote_sig_id, channel->remote_cid, flags, 0, 4, &config_options);
658                         channelStateVarClearFlag(channel,L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_MTU);
659                     } else {
660                         l2cap_send_signaling_packet(channel->handle, CONFIGURE_RESPONSE, channel->remote_sig_id, channel->remote_cid, flags, 0, 0, NULL);
661                     }
662                     channelStateVarClearFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_CONT);
663                 }
664                 else if (channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ){
665                     channelStateVarClearFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
666                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SENT_CONF_REQ);
667                     channel->local_sig_id = l2cap_next_sig_id();
668                     config_options[0] = 1; // MTU
669                     config_options[1] = 2; // len param
670                     bt_store_16( (uint8_t*)&config_options, 2, channel->local_mtu);
671                     l2cap_send_signaling_packet(channel->handle, CONFIGURE_REQUEST, channel->local_sig_id, channel->remote_cid, 0, 4, &config_options);
672                     l2cap_start_rtx(channel);
673                 }
674                 if (l2cap_channel_ready_for_open(channel)){
675                     channel->state = L2CAP_STATE_OPEN;
676                     l2cap_emit_channel_opened(channel, 0);  // success
677                     l2cap_emit_credits(channel, 1);
678                 }
679                 break;
680 
681             case L2CAP_STATE_WILL_SEND_DISCONNECT_RESPONSE:
682                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
683                 l2cap_send_signaling_packet( channel->handle, DISCONNECTION_RESPONSE, channel->remote_sig_id, channel->local_cid, channel->remote_cid);
684                 // we don't start an RTX timer for a disconnect - there's no point in closing the channel if the other side doesn't respond :)
685                 l2cap_finialize_channel_close(channel);  // -- remove from list
686                 break;
687 
688             case L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST:
689                 if (!hci_can_send_acl_packet_now(channel->handle)) break;
690                 channel->local_sig_id = l2cap_next_sig_id();
691                 channel->state = L2CAP_STATE_WAIT_DISCONNECT;
692                 l2cap_send_signaling_packet( channel->handle, DISCONNECTION_REQUEST, channel->local_sig_id, channel->remote_cid, channel->local_cid);
693                 break;
694             default:
695                 break;
696         }
697     }
698 
699 #ifdef HAVE_BLE
700     // send l2cap con paramter update if necessary
701     hci_connections_get_iterator(&it);
702     while(linked_list_iterator_has_next(&it)){
703         hci_connection_t * connection = (hci_connection_t *) linked_list_iterator_next(&it);
704         int result;
705 
706         switch (connection->le_con_parameter_update_state){
707             case CON_PARAMETER_UPDATE_SEND_RESPONSE:
708                 result = 0;
709                 break;
710             case CON_PARAMETER_UPDATE_DENY:
711                 result = 1;
712                 break;
713             default:
714                 result = -1;
715                 break;
716         }
717         if (result < 0) break;
718 
719         if (!hci_can_send_acl_packet_now(connection->con_handle)) break;
720         hci_reserve_packet_buffer();
721         uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
722         connection->le_con_parameter_update_state = CON_PARAMETER_UPDATE_CHANGE_HCI_CON_PARAMETERS;
723         uint16_t len = l2cap_le_create_connection_parameter_update_response(acl_buffer, connection->con_handle, 0);
724         hci_send_acl_packet_buffer(len);
725     }
726 #endif
727 
728 }
729 
730 uint16_t l2cap_max_mtu(void){
731     return HCI_ACL_PAYLOAD_SIZE - L2CAP_HEADER_SIZE;
732 }
733 
734 uint16_t l2cap_max_le_mtu(){
735     return l2cap_max_mtu();
736 }
737 
738 static void l2cap_handle_connection_complete(uint16_t handle, l2cap_channel_t * channel){
739     if (channel->state == L2CAP_STATE_WAIT_CONNECTION_COMPLETE || channel->state == L2CAP_STATE_WILL_SEND_CREATE_CONNECTION) {
740         log_info("l2cap_handle_connection_complete expected state");
741         // success, start l2cap handshake
742         channel->handle = handle;
743         channel->local_cid = l2cap_next_local_cid();
744         // check remote SSP feature first
745         channel->state = L2CAP_STATE_WAIT_REMOTE_SUPPORTED_FEATURES;
746     }
747 }
748 
749 static void l2cap_handle_remote_supported_features_received(l2cap_channel_t * channel){
750     if (channel->state != L2CAP_STATE_WAIT_REMOTE_SUPPORTED_FEATURES) return;
751 
752     // we have been waiting for remote supported features, if both support SSP,
753     log_info("l2cap received remote supported features, sec_level_0_allowed for psm %u = %u", channel->psm, l2cap_security_level_0_allowed_for_PSM(channel->psm));
754     if (hci_ssp_supported_on_both_sides(channel->handle) && !l2cap_security_level_0_allowed_for_PSM(channel->psm)){
755         // request security level 2
756         channel->state = L2CAP_STATE_WAIT_OUTGOING_SECURITY_LEVEL_UPDATE;
757         gap_request_security_level(channel->handle, LEVEL_2);
758         return;
759     }
760     // fine, go ahead
761     channel->state = L2CAP_STATE_WILL_SEND_CONNECTION_REQUEST;
762 }
763 
764 // open outgoing L2CAP channel
765 void l2cap_create_channel_internal(void * connection, btstack_packet_handler_t packet_handler,
766                                    bd_addr_t address, uint16_t psm, uint16_t mtu){
767 
768     log_info("L2CAP_CREATE_CHANNEL_MTU addr %s psm 0x%x mtu %u", bd_addr_to_str(address), psm, mtu);
769 
770     // alloc structure
771     l2cap_channel_t * chan = btstack_memory_l2cap_channel_get();
772     if (!chan) {
773         // emit error event
774         l2cap_channel_t dummy_channel;
775         BD_ADDR_COPY(dummy_channel.address, address);
776         dummy_channel.psm = psm;
777         l2cap_emit_channel_opened(&dummy_channel, BTSTACK_MEMORY_ALLOC_FAILED);
778         return;
779     }
780     // Init memory (make valgrind happy)
781     memset(chan, 0, sizeof(l2cap_channel_t));
782     // limit local mtu to max acl packet length - l2cap header
783     if (mtu > l2cap_max_mtu()) {
784         mtu = l2cap_max_mtu();
785     }
786 
787     // fill in
788     BD_ADDR_COPY(chan->address, address);
789     chan->psm = psm;
790     chan->handle = 0;
791     chan->connection = connection;
792     chan->packet_handler = packet_handler;
793     chan->remote_mtu = L2CAP_MINIMAL_MTU;
794     chan->local_mtu = mtu;
795     chan->packets_granted = 0;
796 
797     // set initial state
798     chan->state = L2CAP_STATE_WILL_SEND_CREATE_CONNECTION;
799     chan->state_var = L2CAP_CHANNEL_STATE_VAR_NONE;
800     chan->remote_sig_id = L2CAP_SIG_ID_INVALID;
801     chan->local_sig_id = L2CAP_SIG_ID_INVALID;
802     chan->required_security_level = LEVEL_0;
803 
804     // add to connections list
805     linked_list_add(&l2cap_channels, (linked_item_t *) chan);
806 
807     // check if hci connection is already usable
808     hci_connection_t * conn = hci_connection_for_bd_addr_and_type(address, BD_ADDR_TYPE_CLASSIC);
809     if (conn){
810         log_info("l2cap_create_channel_internal, hci connection already exists");
811         l2cap_handle_connection_complete(conn->con_handle, chan);
812         // check ir remote supported fearures are already received
813         if (conn->bonding_flags & BONDING_RECEIVED_REMOTE_FEATURES) {
814             l2cap_handle_remote_supported_features_received(chan);
815         }
816     }
817 
818     l2cap_run();
819 }
820 
821 void l2cap_disconnect_internal(uint16_t local_cid, uint8_t reason){
822     log_info("L2CAP_DISCONNECT local_cid 0x%x reason 0x%x", local_cid, reason);
823     // find channel for local_cid
824     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
825     if (channel) {
826         channel->state = L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST;
827     }
828     // process
829     l2cap_run();
830 }
831 
832 static void l2cap_handle_connection_failed_for_addr(bd_addr_t address, uint8_t status){
833     linked_list_iterator_t it;
834     linked_list_iterator_init(&it, &l2cap_channels);
835     while (linked_list_iterator_has_next(&it)){
836         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
837         if ( BD_ADDR_CMP( channel->address, address) != 0) continue;
838         // channel for this address found
839         switch (channel->state){
840             case L2CAP_STATE_WAIT_CONNECTION_COMPLETE:
841             case L2CAP_STATE_WILL_SEND_CREATE_CONNECTION:
842                 // failure, forward error code
843                 l2cap_emit_channel_opened(channel, status);
844                 // discard channel
845                 l2cap_stop_rtx(channel);
846                 linked_list_iterator_remove(&it);
847                 btstack_memory_l2cap_channel_free(channel);
848                 break;
849             default:
850                 break;
851         }
852     }
853 }
854 
855 static void l2cap_handle_connection_success_for_addr(bd_addr_t address, hci_con_handle_t handle){
856     linked_list_iterator_t it;
857     linked_list_iterator_init(&it, &l2cap_channels);
858     while (linked_list_iterator_has_next(&it)){
859         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
860         if ( ! BD_ADDR_CMP( channel->address, address) ){
861             l2cap_handle_connection_complete(handle, channel);
862         }
863     }
864     // process
865     l2cap_run();
866 }
867 
868 void l2cap_event_handler(uint8_t *packet, uint16_t size){
869 
870     bd_addr_t address;
871     hci_con_handle_t handle;
872     linked_list_iterator_t it;
873     int hci_con_used;
874 
875     switch(packet[0]){
876 
877         // handle connection complete events
878         case HCI_EVENT_CONNECTION_COMPLETE:
879             bt_flip_addr(address, &packet[5]);
880             if (packet[2] == 0){
881                 handle = READ_BT_16(packet, 3);
882                 l2cap_handle_connection_success_for_addr(address, handle);
883             } else {
884                 l2cap_handle_connection_failed_for_addr(address, packet[2]);
885             }
886             break;
887 
888         // handle successful create connection cancel command
889         case HCI_EVENT_COMMAND_COMPLETE:
890             if ( COMMAND_COMPLETE_EVENT(packet, hci_create_connection_cancel) ) {
891                 if (packet[5] == 0){
892                     bt_flip_addr(address, &packet[6]);
893                     // CONNECTION TERMINATED BY LOCAL HOST (0X16)
894                     l2cap_handle_connection_failed_for_addr(address, 0x16);
895                 }
896             }
897             l2cap_run();    // try sending signaling packets first
898             break;
899 
900         case HCI_EVENT_COMMAND_STATUS:
901             l2cap_run();    // try sending signaling packets first
902             break;
903 
904         // handle disconnection complete events
905         case HCI_EVENT_DISCONNECTION_COMPLETE:
906             // send l2cap disconnect events for all channels on this handle and free them
907             handle = READ_BT_16(packet, 3);
908             linked_list_iterator_init(&it, &l2cap_channels);
909             while (linked_list_iterator_has_next(&it)){
910                 l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
911                 if (channel->handle != handle) continue;
912                 l2cap_emit_channel_closed(channel);
913                 l2cap_stop_rtx(channel);
914                 linked_list_iterator_remove(&it);
915                 btstack_memory_l2cap_channel_free(channel);
916             }
917             break;
918 
919         case HCI_EVENT_NUMBER_OF_COMPLETED_PACKETS:
920             l2cap_run();    // try sending signaling packets first
921             l2cap_hand_out_credits();
922             break;
923 
924         // HCI Connection Timeouts
925         case L2CAP_EVENT_TIMEOUT_CHECK:
926             handle = READ_BT_16(packet, 2);
927             if (hci_authentication_active_for_handle(handle)) break;
928             hci_con_used = 0;
929             linked_list_iterator_init(&it, &l2cap_channels);
930             while (linked_list_iterator_has_next(&it)){
931                 l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
932                 if (channel->handle != handle) continue;
933                 hci_con_used = 1;
934                 break;
935             }
936             if (hci_con_used) break;
937             if (!hci_can_send_command_packet_now()) break;
938             hci_send_cmd(&hci_disconnect, handle, 0x13); // remote closed connection
939             break;
940 
941         case DAEMON_EVENT_HCI_PACKET_SENT:
942             linked_list_iterator_init(&it, &l2cap_channels);
943             while (linked_list_iterator_has_next(&it)){
944                 l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
945                 if (!channel->packet_handler) continue;
946                 (* (channel->packet_handler))(HCI_EVENT_PACKET, channel->local_cid, packet, size);
947             }
948             if (attribute_protocol_packet_handler) {
949                 (*attribute_protocol_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
950             }
951             if (security_protocol_packet_handler) {
952                 (*security_protocol_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
953             }
954             if (connectionless_channel_packet_handler) {
955                 (*connectionless_channel_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
956             }
957             break;
958 
959         case HCI_EVENT_READ_REMOTE_SUPPORTED_FEATURES_COMPLETE:
960             handle = READ_BT_16(packet, 3);
961             linked_list_iterator_init(&it, &l2cap_channels);
962             while (linked_list_iterator_has_next(&it)){
963                 l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
964                 if (channel->handle != handle) continue;
965                 l2cap_handle_remote_supported_features_received(channel);
966                 break;
967             }
968             break;
969 
970         case GAP_SECURITY_LEVEL:
971             handle = READ_BT_16(packet, 2);
972             log_info("l2cap - security level update");
973             linked_list_iterator_init(&it, &l2cap_channels);
974             while (linked_list_iterator_has_next(&it)){
975                 l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
976                 if (channel->handle != handle) continue;
977 
978                 log_info("l2cap - state %u", channel->state);
979 
980                 gap_security_level_t actual_level = packet[4];
981                 gap_security_level_t required_level = channel->required_security_level;
982 
983                 switch (channel->state){
984                     case L2CAP_STATE_WAIT_INCOMING_SECURITY_LEVEL_UPDATE:
985                         if (actual_level >= required_level){
986                             channel->state = L2CAP_STATE_WAIT_CLIENT_ACCEPT_OR_REJECT;
987                             l2cap_emit_connection_request(channel);
988                         } else {
989                             channel->reason = 0x03; // security block
990                             channel->state = L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_DECLINE;
991                         }
992                         break;
993 
994                     case L2CAP_STATE_WAIT_OUTGOING_SECURITY_LEVEL_UPDATE:
995                         if (actual_level >= required_level){
996                             channel->state = L2CAP_STATE_WILL_SEND_CONNECTION_REQUEST;
997                         } else {
998                             // disconnnect, authentication not good enough
999                             hci_disconnect_security_block(handle);
1000                         }
1001                         break;
1002 
1003                     default:
1004                         break;
1005                 }
1006             }
1007             break;
1008 
1009         default:
1010             break;
1011     }
1012 
1013     // pass on: main packet handler, att and sm packet handlers
1014     (*packet_handler)(NULL, HCI_EVENT_PACKET, 0, packet, size);
1015     if (attribute_protocol_packet_handler){
1016         (*attribute_protocol_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
1017     }
1018     if (security_protocol_packet_handler) {
1019         (*security_protocol_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
1020     }
1021     if (connectionless_channel_packet_handler) {
1022         (*connectionless_channel_packet_handler)(HCI_EVENT_PACKET, 0, packet, size);
1023     }
1024 
1025     l2cap_run();
1026 }
1027 
1028 static void l2cap_handle_disconnect_request(l2cap_channel_t *channel, uint16_t identifier){
1029     channel->remote_sig_id = identifier;
1030     channel->state = L2CAP_STATE_WILL_SEND_DISCONNECT_RESPONSE;
1031     l2cap_run();
1032 }
1033 
1034 static void l2cap_register_signaling_response(hci_con_handle_t handle, uint8_t code, uint8_t sig_id, uint16_t data){
1035     // Vol 3, Part A, 4.3: "The DCID and SCID fields shall be ignored when the result field indi- cates the connection was refused."
1036     if (signaling_responses_pending < NR_PENDING_SIGNALING_RESPONSES) {
1037         signaling_responses[signaling_responses_pending].handle = handle;
1038         signaling_responses[signaling_responses_pending].code = code;
1039         signaling_responses[signaling_responses_pending].sig_id = sig_id;
1040         signaling_responses[signaling_responses_pending].data = data;
1041         signaling_responses_pending++;
1042         l2cap_run();
1043     }
1044 }
1045 
1046 static void l2cap_handle_connection_request(hci_con_handle_t handle, uint8_t sig_id, uint16_t psm, uint16_t source_cid){
1047 
1048     // log_info("l2cap_handle_connection_request for handle %u, psm %u cid 0x%02x", handle, psm, source_cid);
1049     l2cap_service_t *service = l2cap_get_service(psm);
1050     if (!service) {
1051         // 0x0002 PSM not supported
1052         l2cap_register_signaling_response(handle, CONNECTION_REQUEST, sig_id, 0x0002);
1053         return;
1054     }
1055 
1056     hci_connection_t * hci_connection = hci_connection_for_handle( handle );
1057     if (!hci_connection) {
1058         //
1059         log_error("no hci_connection for handle %u", handle);
1060         return;
1061     }
1062 
1063     // reject connection (0x03 security block) and disconnect if both have SSP, connection is not encrypted and PSM != SDP
1064     if (  hci_ssp_supported_on_both_sides(handle)
1065     &&    gap_security_level(handle) == LEVEL_0
1066     &&   !l2cap_security_level_0_allowed_for_PSM(psm)){
1067 
1068         // 0x0003 Security Block
1069         l2cap_register_signaling_response(handle, CONNECTION_REQUEST, sig_id, 0x0003);
1070         return;
1071     }
1072 
1073 
1074     // alloc structure
1075     // log_info("l2cap_handle_connection_request register channel");
1076     l2cap_channel_t * channel = btstack_memory_l2cap_channel_get();
1077     if (!channel){
1078         // 0x0004 No resources available
1079         l2cap_register_signaling_response(handle, CONNECTION_REQUEST, sig_id, 0x0004);
1080         return;
1081     }
1082     // Init memory (make valgrind happy)
1083     memset(channel, 0, sizeof(l2cap_channel_t));
1084     // fill in
1085     BD_ADDR_COPY(channel->address, hci_connection->address);
1086     channel->psm = psm;
1087     channel->handle = handle;
1088     channel->connection = service->connection;
1089     channel->packet_handler = service->packet_handler;
1090     channel->local_cid  = l2cap_next_local_cid();
1091     channel->remote_cid = source_cid;
1092     channel->local_mtu  = service->mtu;
1093     channel->remote_mtu = L2CAP_DEFAULT_MTU;
1094     channel->packets_granted = 0;
1095     channel->remote_sig_id = sig_id;
1096     channel->required_security_level = service->required_security_level;
1097 
1098     // limit local mtu to max acl packet length - l2cap header
1099     if (channel->local_mtu > l2cap_max_mtu()) {
1100         channel->local_mtu = l2cap_max_mtu();
1101     }
1102 
1103     // set initial state
1104     channel->state =     L2CAP_STATE_WAIT_INCOMING_SECURITY_LEVEL_UPDATE;
1105     channel->state_var = L2CAP_CHANNEL_STATE_VAR_SEND_CONN_RESP_PEND;
1106 
1107     // add to connections list
1108     linked_list_add(&l2cap_channels, (linked_item_t *) channel);
1109 
1110     // assert security requirements
1111     gap_request_security_level(handle, channel->required_security_level);
1112 }
1113 
1114 void l2cap_accept_connection_internal(uint16_t local_cid){
1115     log_info("L2CAP_ACCEPT_CONNECTION local_cid 0x%x", local_cid);
1116     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(local_cid);
1117     if (!channel) {
1118         log_error("l2cap_accept_connection_internal called but local_cid 0x%x not found", local_cid);
1119         return;
1120     }
1121 
1122     channel->state = L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_ACCEPT;
1123 
1124     // process
1125     l2cap_run();
1126 }
1127 
1128 void l2cap_decline_connection_internal(uint16_t local_cid, uint8_t reason){
1129     log_info("L2CAP_DECLINE_CONNECTION local_cid 0x%x, reason %x", local_cid, reason);
1130     l2cap_channel_t * channel = l2cap_get_channel_for_local_cid( local_cid);
1131     if (!channel) {
1132         log_error( "l2cap_decline_connection_internal called but local_cid 0x%x not found", local_cid);
1133         return;
1134     }
1135     channel->state  = L2CAP_STATE_WILL_SEND_CONNECTION_RESPONSE_DECLINE;
1136     channel->reason = reason;
1137     l2cap_run();
1138 }
1139 
1140 void l2cap_signaling_handle_configure_request(l2cap_channel_t *channel, uint8_t *command){
1141 
1142     channel->remote_sig_id = command[L2CAP_SIGNALING_COMMAND_SIGID_OFFSET];
1143 
1144     uint16_t flags = READ_BT_16(command, 6);
1145     if (flags & 1) {
1146         channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_CONT);
1147     }
1148 
1149     // accept the other's configuration options
1150     uint16_t end_pos = 4 + READ_BT_16(command, L2CAP_SIGNALING_COMMAND_LENGTH_OFFSET);
1151     uint16_t pos     = 8;
1152     while (pos < end_pos){
1153         uint8_t option_hint = command[pos] >> 7;
1154         uint8_t option_type = command[pos] & 0x7f;
1155         log_info("l2cap cid %u, hint %u, type %u", channel->local_cid, option_hint, option_type);
1156         pos++;
1157         uint8_t length = command[pos++];
1158         // MTU { type(8): 1, len(8):2, MTU(16) }
1159         if (option_type == 1 && length == 2){
1160             channel->remote_mtu = READ_BT_16(command, pos);
1161             // log_info("l2cap cid 0x%02x, remote mtu %u", channel->local_cid, channel->remote_mtu);
1162             channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_MTU);
1163         }
1164         // Flush timeout { type(8):2, len(8): 2, Flush Timeout(16)}
1165         if (option_type == 2 && length == 2){
1166             channel->flush_timeout = READ_BT_16(command, pos);
1167         }
1168         // check for unknown options
1169         if (option_hint == 0 && (option_type == 0 || option_type >= 0x07)){
1170             log_info("l2cap cid %u, unknown options", channel->local_cid);
1171             channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_INVALID);
1172         }
1173         pos += length;
1174     }
1175 }
1176 
1177 static int l2cap_channel_ready_for_open(l2cap_channel_t *channel){
1178     // log_info("l2cap_channel_ready_for_open 0x%02x", channel->state_var);
1179     if ((channel->state_var & L2CAP_CHANNEL_STATE_VAR_RCVD_CONF_RSP) == 0) return 0;
1180     if ((channel->state_var & L2CAP_CHANNEL_STATE_VAR_SENT_CONF_RSP) == 0) return 0;
1181     return 1;
1182 }
1183 
1184 
1185 void l2cap_signaling_handler_channel(l2cap_channel_t *channel, uint8_t *command){
1186 
1187     uint8_t  code       = command[L2CAP_SIGNALING_COMMAND_CODE_OFFSET];
1188     uint8_t  identifier = command[L2CAP_SIGNALING_COMMAND_SIGID_OFFSET];
1189     uint16_t result = 0;
1190 
1191     log_info("L2CAP signaling handler code %u, state %u", code, channel->state);
1192 
1193     // handle DISCONNECT REQUESTS seperately
1194     if (code == DISCONNECTION_REQUEST){
1195         switch (channel->state){
1196             case L2CAP_STATE_CONFIG:
1197             case L2CAP_STATE_OPEN:
1198             case L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST:
1199             case L2CAP_STATE_WAIT_DISCONNECT:
1200                 l2cap_handle_disconnect_request(channel, identifier);
1201                 break;
1202 
1203             default:
1204                 // ignore in other states
1205                 break;
1206         }
1207         return;
1208     }
1209 
1210     // @STATEMACHINE(l2cap)
1211     switch (channel->state) {
1212 
1213         case L2CAP_STATE_WAIT_CONNECT_RSP:
1214             switch (code){
1215                 case CONNECTION_RESPONSE:
1216                     l2cap_stop_rtx(channel);
1217                     result = READ_BT_16 (command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET+4);
1218                     switch (result) {
1219                         case 0:
1220                             // successful connection
1221                             channel->remote_cid = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
1222                             channel->state = L2CAP_STATE_CONFIG;
1223                             channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
1224                             break;
1225                         case 1:
1226                             // connection pending. get some coffee, but start the ERTX
1227                             l2cap_start_ertx(channel);
1228                             break;
1229                         default:
1230                             // channel closed
1231                             channel->state = L2CAP_STATE_CLOSED;
1232                             // map l2cap connection response result to BTstack status enumeration
1233                             l2cap_emit_channel_opened(channel, L2CAP_CONNECTION_RESPONSE_RESULT_SUCCESSFUL + result);
1234 
1235                             // drop link key if security block
1236                             if (L2CAP_CONNECTION_RESPONSE_RESULT_SUCCESSFUL + result == L2CAP_CONNECTION_RESPONSE_RESULT_REFUSED_SECURITY){
1237                                 hci_drop_link_key_for_bd_addr(channel->address);
1238                             }
1239 
1240                             // discard channel
1241                             linked_list_remove(&l2cap_channels, (linked_item_t *) channel);
1242                             btstack_memory_l2cap_channel_free(channel);
1243                             break;
1244                     }
1245                     break;
1246 
1247                 default:
1248                     //@TODO: implement other signaling packets
1249                     break;
1250             }
1251             break;
1252 
1253         case L2CAP_STATE_CONFIG:
1254             result = READ_BT_16 (command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET+4);
1255             switch (code) {
1256                 case CONFIGURE_REQUEST:
1257                     channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP);
1258                     l2cap_signaling_handle_configure_request(channel, command);
1259                     if (!(channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_CONT)){
1260                         // only done if continuation not set
1261                         channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_RCVD_CONF_REQ);
1262                     }
1263                     break;
1264                 case CONFIGURE_RESPONSE:
1265                     l2cap_stop_rtx(channel);
1266                     switch (result){
1267                         case 0: // success
1268                             channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_RCVD_CONF_RSP);
1269                             break;
1270                         case 4: // pending
1271                             l2cap_start_ertx(channel);
1272                             break;
1273                         default:
1274                             // retry on negative result
1275                             channelStateVarSetFlag(channel, L2CAP_CHANNEL_STATE_VAR_SEND_CONF_REQ);
1276                             break;
1277                     }
1278                     break;
1279                 default:
1280                     break;
1281             }
1282             if (l2cap_channel_ready_for_open(channel)){
1283                 // for open:
1284                 channel->state = L2CAP_STATE_OPEN;
1285                 l2cap_emit_channel_opened(channel, 0);
1286                 l2cap_emit_credits(channel, 1);
1287             }
1288             break;
1289 
1290         case L2CAP_STATE_WAIT_DISCONNECT:
1291             switch (code) {
1292                 case DISCONNECTION_RESPONSE:
1293                     l2cap_finialize_channel_close(channel);
1294                     break;
1295                 default:
1296                     //@TODO: implement other signaling packets
1297                     break;
1298             }
1299             break;
1300 
1301         case L2CAP_STATE_CLOSED:
1302             // @TODO handle incoming requests
1303             break;
1304 
1305         case L2CAP_STATE_OPEN:
1306             //@TODO: implement other signaling packets, e.g. re-configure
1307             break;
1308         default:
1309             break;
1310     }
1311     // log_info("new state %u", channel->state);
1312 }
1313 
1314 
1315 void l2cap_signaling_handler_dispatch( hci_con_handle_t handle, uint8_t * command){
1316 
1317     // get code, signalind identifier and command len
1318     uint8_t code   = command[L2CAP_SIGNALING_COMMAND_CODE_OFFSET];
1319     uint8_t sig_id = command[L2CAP_SIGNALING_COMMAND_SIGID_OFFSET];
1320 
1321     // not for a particular channel, and not CONNECTION_REQUEST, ECHO_[REQUEST|RESPONSE], INFORMATION_REQUEST
1322     if (code < 1 || code == ECHO_RESPONSE || code > INFORMATION_REQUEST){
1323         l2cap_register_signaling_response(handle, COMMAND_REJECT, sig_id, L2CAP_REJ_CMD_UNKNOWN);
1324         return;
1325     }
1326 
1327     // general commands without an assigned channel
1328     switch(code) {
1329 
1330         case CONNECTION_REQUEST: {
1331             uint16_t psm =        READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
1332             uint16_t source_cid = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET+2);
1333             l2cap_handle_connection_request(handle, sig_id, psm, source_cid);
1334             return;
1335         }
1336 
1337         case ECHO_REQUEST:
1338             l2cap_register_signaling_response(handle, code, sig_id, 0);
1339             return;
1340 
1341         case INFORMATION_REQUEST: {
1342             uint16_t infoType = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
1343             l2cap_register_signaling_response(handle, code, sig_id, infoType);
1344             return;
1345         }
1346 
1347         default:
1348             break;
1349     }
1350 
1351 
1352     // Get potential destination CID
1353     uint16_t dest_cid = READ_BT_16(command, L2CAP_SIGNALING_COMMAND_DATA_OFFSET);
1354 
1355     // Find channel for this sig_id and connection handle
1356     linked_list_iterator_t it;
1357     linked_list_iterator_init(&it, &l2cap_channels);
1358     while (linked_list_iterator_has_next(&it)){
1359         l2cap_channel_t * channel = (l2cap_channel_t *) linked_list_iterator_next(&it);
1360         if (channel->handle != handle) continue;
1361         if (code & 1) {
1362             // match odd commands (responses) by previous signaling identifier
1363             if (channel->local_sig_id == sig_id) {
1364                 l2cap_signaling_handler_channel(channel, command);
1365                 break;
1366             }
1367         } else {
1368             // match even commands (requests) by local channel id
1369             if (channel->local_cid == dest_cid) {
1370                 l2cap_signaling_handler_channel(channel, command);
1371                 break;
1372             }
1373         }
1374     }
1375 }
1376 
1377 void l2cap_acl_handler( uint8_t *packet, uint16_t size ){
1378 
1379     // Get Channel ID
1380     uint16_t channel_id = READ_L2CAP_CHANNEL_ID(packet);
1381     hci_con_handle_t handle = READ_ACL_CONNECTION_HANDLE(packet);
1382 
1383     switch (channel_id) {
1384 
1385         case L2CAP_CID_SIGNALING: {
1386 
1387             uint16_t command_offset = 8;
1388             while (command_offset < size) {
1389 
1390                 // handle signaling commands
1391                 l2cap_signaling_handler_dispatch(handle, &packet[command_offset]);
1392 
1393                 // increment command_offset
1394                 command_offset += L2CAP_SIGNALING_COMMAND_DATA_OFFSET + READ_BT_16(packet, command_offset + L2CAP_SIGNALING_COMMAND_LENGTH_OFFSET);
1395             }
1396             break;
1397         }
1398 
1399         case L2CAP_CID_ATTRIBUTE_PROTOCOL:
1400             if (attribute_protocol_packet_handler) {
1401                 (*attribute_protocol_packet_handler)(ATT_DATA_PACKET, handle, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
1402             }
1403             break;
1404 
1405         case L2CAP_CID_SECURITY_MANAGER_PROTOCOL:
1406             if (security_protocol_packet_handler) {
1407                 (*security_protocol_packet_handler)(SM_DATA_PACKET, handle, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
1408             }
1409             break;
1410 
1411         case L2CAP_CID_CONNECTIONLESS_CHANNEL:
1412             if (connectionless_channel_packet_handler) {
1413                 (*connectionless_channel_packet_handler)(UCD_DATA_PACKET, handle, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
1414             }
1415             break;
1416 
1417         case L2CAP_CID_SIGNALING_LE: {
1418             switch (packet[8]){
1419                 case CONNECTION_PARAMETER_UPDATE_RESPONSE: {
1420                     uint16_t result = READ_BT_16(packet, 12);
1421                     l2cap_emit_connection_parameter_update_response(handle, result);
1422                     break;
1423                 }
1424                 case CONNECTION_PARAMETER_UPDATE_REQUEST: {
1425                     uint8_t event[10];
1426                     event[0] = L2CAP_EVENT_CONNECTION_PARAMETER_UPDATE_REQUEST;
1427                     event[1] = 8;
1428                     memcpy(&event[2], &packet[12], 8);
1429 
1430                     hci_connection_t * connection = hci_connection_for_handle(handle);
1431                     if (connection){
1432                         int update_parameter = 1;
1433                         le_connection_parameter_range_t existing_range = gap_le_get_connection_parameter_range();
1434                         uint16_t le_conn_interval_min = READ_BT_16(packet,12);
1435                         uint16_t le_conn_interval_max = READ_BT_16(packet,14);
1436                         uint16_t le_conn_latency = READ_BT_16(packet,16);
1437                         uint16_t le_supervision_timeout = READ_BT_16(packet,18);
1438 
1439                         if (le_conn_interval_min < existing_range.le_conn_interval_min) update_parameter = 0;
1440                         if (le_conn_interval_max > existing_range.le_conn_interval_max) update_parameter = 0;
1441 
1442                         if (le_conn_latency < existing_range.le_conn_latency_min) update_parameter = 0;
1443                         if (le_conn_latency > existing_range.le_conn_latency_max) update_parameter = 0;
1444 
1445                         if (le_supervision_timeout < existing_range.le_supervision_timeout_min) update_parameter = 0;
1446                         if (le_supervision_timeout > existing_range.le_supervision_timeout_max) update_parameter = 0;
1447 
1448                         if (update_parameter){
1449                             connection->le_con_parameter_update_state = CON_PARAMETER_UPDATE_SEND_RESPONSE;
1450                             connection->le_conn_interval_min = le_conn_interval_min;
1451                             connection->le_conn_interval_max = le_conn_interval_max;
1452                             connection->le_conn_latency = le_conn_latency;
1453                             connection->le_supervision_timeout = le_supervision_timeout;
1454                         } else {
1455                             connection->le_con_parameter_update_state = CON_PARAMETER_UPDATE_DENY;
1456                         }
1457                     }
1458 
1459                     hci_dump_packet( HCI_EVENT_PACKET, 0, event, sizeof(event));
1460                     (*packet_handler)(NULL, HCI_EVENT_PACKET, 0, event, sizeof(event));
1461 
1462                     break;
1463                 }
1464                 default: {
1465                     uint8_t sig_id = packet[COMPLETE_L2CAP_HEADER + 1];
1466                     l2cap_register_signaling_response(handle, COMMAND_REJECT_LE, sig_id, L2CAP_REJ_CMD_UNKNOWN);
1467                     break;
1468                 }
1469             }
1470             break;
1471         }
1472 
1473         default: {
1474             // Find channel for this channel_id and connection handle
1475             l2cap_channel_t * channel = l2cap_get_channel_for_local_cid(channel_id);
1476             if (channel) {
1477                 l2cap_dispatch(channel, L2CAP_DATA_PACKET, &packet[COMPLETE_L2CAP_HEADER], size-COMPLETE_L2CAP_HEADER);
1478             }
1479             break;
1480         }
1481     }
1482 }
1483 
1484 static void l2cap_packet_handler(uint8_t packet_type, uint8_t *packet, uint16_t size){
1485     switch (packet_type) {
1486         case HCI_EVENT_PACKET:
1487             l2cap_event_handler(packet, size);
1488             break;
1489         case HCI_ACL_DATA_PACKET:
1490             l2cap_acl_handler(packet, size);
1491             break;
1492         default:
1493             break;
1494     }
1495     l2cap_run();
1496 }
1497 
1498 // finalize closed channel - l2cap_handle_disconnect_request & DISCONNECTION_RESPONSE
1499 void l2cap_finialize_channel_close(l2cap_channel_t *channel){
1500     channel->state = L2CAP_STATE_CLOSED;
1501     l2cap_emit_channel_closed(channel);
1502     // discard channel
1503     l2cap_stop_rtx(channel);
1504     linked_list_remove(&l2cap_channels, (linked_item_t *) channel);
1505     btstack_memory_l2cap_channel_free(channel);
1506 }
1507 
1508 l2cap_service_t * l2cap_get_service(uint16_t psm){
1509     linked_list_iterator_t it;
1510     linked_list_iterator_init(&it, &l2cap_services);
1511     while (linked_list_iterator_has_next(&it)){
1512         l2cap_service_t * service = (l2cap_service_t *) linked_list_iterator_next(&it);
1513         if ( service->psm == psm){
1514             return service;
1515         };
1516     }
1517     return NULL;
1518 }
1519 
1520 void l2cap_register_service_internal(void *connection, btstack_packet_handler_t packet_handler, uint16_t psm, uint16_t mtu, gap_security_level_t security_level){
1521 
1522     log_info("L2CAP_REGISTER_SERVICE psm 0x%x mtu %u connection %p", psm, mtu, connection);
1523 
1524     // check for alread registered psm
1525     // TODO: emit error event
1526     l2cap_service_t *service = l2cap_get_service(psm);
1527     if (service) {
1528         log_error("l2cap_register_service_internal: PSM %u already registered", psm);
1529         l2cap_emit_service_registered(connection, L2CAP_SERVICE_ALREADY_REGISTERED, psm);
1530         return;
1531     }
1532 
1533     // alloc structure
1534     // TODO: emit error event
1535     service = btstack_memory_l2cap_service_get();
1536     if (!service) {
1537         log_error("l2cap_register_service_internal: no memory for l2cap_service_t");
1538         l2cap_emit_service_registered(connection, BTSTACK_MEMORY_ALLOC_FAILED, psm);
1539         return;
1540     }
1541 
1542     // fill in
1543     service->psm = psm;
1544     service->mtu = mtu;
1545     service->connection = connection;
1546     service->packet_handler = packet_handler;
1547     service->required_security_level = security_level;
1548 
1549     // add to services list
1550     linked_list_add(&l2cap_services, (linked_item_t *) service);
1551 
1552     // enable page scan
1553     hci_connectable_control(1);
1554 
1555     // done
1556     l2cap_emit_service_registered(connection, 0, psm);
1557 }
1558 
1559 void l2cap_unregister_service_internal(void *connection, uint16_t psm){
1560 
1561     log_info("L2CAP_UNREGISTER_SERVICE psm 0x%x", psm);
1562 
1563     l2cap_service_t *service = l2cap_get_service(psm);
1564     if (!service) return;
1565     linked_list_remove(&l2cap_services, (linked_item_t *) service);
1566     btstack_memory_l2cap_service_free(service);
1567 
1568     // disable page scan when no services registered
1569     if (!linked_list_empty(&l2cap_services)) return;
1570     hci_connectable_control(0);
1571 }
1572 
1573 
1574 // Bluetooth 4.0 - allows to register handler for Attribute Protocol and Security Manager Protocol
1575 void l2cap_register_fixed_channel(btstack_packet_handler_t packet_handler, uint16_t channel_id) {
1576     switch(channel_id){
1577         case L2CAP_CID_ATTRIBUTE_PROTOCOL:
1578             attribute_protocol_packet_handler = packet_handler;
1579             break;
1580         case L2CAP_CID_SECURITY_MANAGER_PROTOCOL:
1581             security_protocol_packet_handler = packet_handler;
1582             break;
1583         case L2CAP_CID_CONNECTIONLESS_CHANNEL:
1584             connectionless_channel_packet_handler = packet_handler;
1585             break;
1586     }
1587 }
1588 
1589 #ifdef HAVE_BLE
1590 
1591 // Request LE connection parameter update
1592 int l2cap_le_request_connection_parameter_update(uint16_t handle, uint16_t interval_min, uint16_t interval_max, uint16_t slave_latency, uint16_t timeout_multiplier){
1593     if (!hci_can_send_acl_packet_now(handle)){
1594         log_info("l2cap_send_signaling_packet, cannot send");
1595         return BTSTACK_ACL_BUFFERS_FULL;
1596     }
1597     // log_info("l2cap_send_signaling_packet type %u", cmd);
1598     hci_reserve_packet_buffer();
1599     uint8_t *acl_buffer = hci_get_outgoing_packet_buffer();
1600     uint16_t len = l2cap_le_create_connection_parameter_update_request(acl_buffer, handle, interval_min, interval_max, slave_latency, timeout_multiplier);
1601     return hci_send_acl_packet_buffer(len);
1602 }
1603 #endif
1604 
1605