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l2cap: send fcs option from ertm config, use fcs if either side requested it

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This commit is contained in:
Matthias Ringwald 2024-11-03 23:18:52 +01:00
parent 5d59e25a1a
commit d75fc2605a
2 changed files with 15 additions and 11 deletions
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21
src/l2cap.c
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@ -526,11 +526,12 @@ static uint16_t l2cap_setup_options_ertm_request(l2cap_channel_t * channel, uint
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;
// fcs_option = 2 <=> OMIT FCS Omit
if (channel->fcs_option < 2){
config_options[pos++] = L2CAP_CONFIG_OPTION_TYPE_FRAME_CHECK_SEQUENCE;
config_options[pos++] = 1; // length
config_options[pos++] = channel->fcs_option;
}
return pos; // 11+4+3=18
}
@ -1507,7 +1508,7 @@ uint8_t l2cap_send_prepared(uint16_t local_cid, uint16_t len){
int fcs_size = 0;
#ifdef ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE
if (channel->mode == L2CAP_CHANNEL_MODE_ENHANCED_RETRANSMISSION && channel->fcs_option){
if (channel->mode == L2CAP_CHANNEL_MODE_ENHANCED_RETRANSMISSION && channel->fcs_active){
fcs_size = 2;
}
#endif
@ -1518,7 +1519,7 @@ uint8_t l2cap_send_prepared(uint16_t local_cid, uint16_t len){
l2cap_setup_header(acl_buffer, channel->con_handle, packet_boundary_flag, channel->remote_cid, len + fcs_size);
#ifdef ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE
if (fcs_size){
if (fcs_size > 0){
// calculate FCS over l2cap data
uint16_t fcs = crc16_calc(acl_buffer + 4, 4 + len);
log_info("I-Frame: fcs 0x%04x", fcs);
@ -3340,7 +3341,7 @@ static void l2cap_signaling_handle_configure_request(l2cap_channel_t *channel, u
// "FCS" has precedence over "No FCS"
uint8_t update = channel->fcs_option || use_fcs;
log_info("local fcs: %u, remote fcs: %u -> %u", channel->fcs_option, use_fcs, update);
channel->fcs_option = update;
channel->fcs_active = update;
// If ERTM mandatory, but remote didn't send Retransmission and Flowcontrol options -> disconnect
if (((channel->state_var & L2CAP_CHANNEL_STATE_VAR_SEND_CONF_RSP_ERTM) == 0) & (channel->ertm_mandatory)){
channel->state = L2CAP_STATE_WILL_SEND_DISCONNECT_REQUEST;
@ -4605,12 +4606,12 @@ static void l2cap_acl_classic_handler_for_channel(l2cap_channel_t * l2cap_channe
#ifdef ENABLE_L2CAP_ENHANCED_RETRANSMISSION_MODE
if (l2cap_channel->mode == L2CAP_CHANNEL_MODE_ENHANCED_RETRANSMISSION){
int fcs_size = l2cap_channel->fcs_option ? 2 : 0;
int fcs_size = l2cap_channel->fcs_active ? 2 : 0;
// assert control + FCS fields are inside
if (size < COMPLETE_L2CAP_HEADER+2+fcs_size) return;
if (l2cap_channel->fcs_option){
if (fcs_size > 0){
// verify FCS (required if one side requested it)
uint16_t fcs_calculated = crc16_calc(&packet[4], size - (4+2));
uint16_t fcs_packet = little_endian_read_16(packet, size-2);

5
src/l2cap.h
View File

@ -316,9 +316,12 @@ typedef struct {
// if ertm is not mandatory, allow fallback to L2CAP Basic Mode - flag
uint8_t ertm_mandatory;
// Frame Chech Sequence (crc16) is present in both directions
// Frame Check Sequence local (from ertm config)
uint8_t fcs_option;
// Frame Check Sequence was requested by either side
bool fcs_active;
// sender: max num of stored outgoing frames
uint8_t num_tx_buffers;