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fix(modem): Document CMUX compatibility issue with CAVLI C16QS

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Closes https://github.com/espressif/esp-protocols/issues/507
This commit is contained in:
David Cermak
2024-11-07 12:31:32 +01:00
parent c5653ff204
commit cc2741d4ad
1 changed files with 32 additions and 0 deletions
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32
docs/esp_modem/en/README.rst
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@ -234,3 +234,35 @@ this patch to adapt the exit sequence https://github.com/espressif/esp-protocols
if ((frame_header[3] & 1) == 0) {
if (frame_header_offset + frame.len <= 4) {
frame_header_offset += frame.len;
4) Device CAVLI C16QS does not correctly enter CMUX mode with esp_modem.
The CMUX as defined in 3GPP TS 27.010: SABM response (paragraph 5.4.1)
should be a UA frame (upon success, DM frame on failure).
This device however responds with 0x3F, which is neither UA nor DM.
You can apply the below patch to adapt the entry sequence
::
diff --git a/components/esp_modem/src/esp_modem_cmux.cpp b/components/esp_modem/src/esp_modem_cmux.cpp
index c47e13b..7afbf73 100644
--- a/components/esp_modem/src/esp_modem_cmux.cpp
+++ b/components/esp_modem/src/esp_modem_cmux.cpp
@@ -137,7 +137,8 @@ bool CMux::data_available(uint8_t *data, size_t len)
} else {
return false;
}
- } else if (data == nullptr && type == (FT_UA | PF) && len == 0) { // notify the initial SABM command
+ } else if (data == nullptr && (type == (FT_UA | PF) || type == 0x3f) && len == 0) { // notify the initial SABM command
Scoped<Lock> l(lock);
sabm_ack = dlci;
} else if (data == nullptr && dlci > 0) {
@@ -238,8 +239,7 @@ bool CMux::on_header(CMuxFrame &frame)
type = frame_header[2];
// Sanity check for expected values of DLCI and type,
// since CRC could be evaluated after the frame payload gets received
- if (dlci > MAX_TERMINALS_NUM || (frame_header[1] & 0x01) == 0 ||
- (((type & FT_UIH) != FT_UIH) && type != (FT_UA | PF) ) ) {
+ if (dlci > MAX_TERMINALS_NUM) {
recover_protocol(protocol_mismatch_reason::UNEXPECTED_HEADER);
return true;
}