l2cap: add fcs_option to ERTM config l2cap_ertm_config_t

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ### Added
 - L2CAP: emit L2CAP_EVENT_ERTM_BUFFER_RELEASED if ERTM buffer not needed/used anymore
+- L2CAP: add fcs_option to ERTM config l2cap_ertm_config_t
 
 ## Changes December 2018
 

example/avrcp_browsing_client.c

@@ -127,6 +127,7 @@ static l2cap_ertm_config_t ertm_config = {
     144,    // l2cap ertm mtu
     4,
     4,
+    0,      // No FCS
 };
 
 

src/classic/goep_client.c

@@ -112,6 +112,7 @@ static l2cap_ertm_config_t ertm_config = {
     512,    // l2cap ertm mtu
     2,
     2,
+    0,      // No FCS
 };
 #endif
 

src/l2cap.c

@@ -408,7 +408,9 @@ static uint16_t l2cap_setup_options_ertm_request(l2cap_channel_t * channel, uint
     config_options[pos++] = 2;     // length
     little_endian_store_16(config_options, pos, channel->local_mtu);
     pos += 2;
-    // 
+
+    // Issue: iOS (e.g. 10.2) uses "No FCS" as default while Core 5.0 specifies "FCS" as default
+    // Workaround: try to actively negotiate FCS option
     config_options[pos++] = L2CAP_CONFIG_OPTION_TYPE_FRAME_CHECK_SEQUENCE;
     config_options[pos++] = 1;     // length
     config_options[pos++] = channel->fcs_option;
@@ -521,10 +523,7 @@ static void l2cap_ertm_configure_channel(l2cap_channel_t * channel, l2cap_ertm_c
     pos += ertm_config->num_rx_buffers * channel->local_mps;
     channel->tx_packets_data = &buffer[pos];
 
-    // Issue: iOS (e.g. 10.2) uses "No FCS" as default while Core 5.0 specifies "FCS" as default
-    // Workaround: try to actively negotiate "No FCS" and fall back to "FCS" if "No FCS" is rejected
-    // This works as iOS accepts the "No FCS" request, hence the default value is only used on non-iOS devices
-    channel->fcs_option = 0;
+    channel->fcs_option = ertm_config->fcs_option;
 }
 
 uint8_t l2cap_create_ertm_channel(btstack_packet_handler_t packet_handler, bd_addr_t address, uint16_t psm, 

src/l2cap.h

@@ -159,6 +159,9 @@ typedef struct {
     // Number of packets that can be received out of order (-> our tx_window size)
     uint8_t num_rx_buffers;
 
+    // Frame Check Sequence (FCS) Option
+    uint8_t fcs_option;
+
 } l2cap_ertm_config_t;
 
 // info regarding an actual channel