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modem: cmux: improve handling of receive buffer overrun

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This allows to properly drop single CMUX frames that are
too big to fit in the receive buffer, keeping track of
where they end so that following frames are received
correctly regardless of the data contents.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>
This commit is contained in:
Tomi Fontanilles 2024-02-14 06:08:26 +02:00 committed by Fabio Baltieri
parent bc64c91d62
commit 90f1ed6a81
1 changed files with 11 additions and 12 deletions
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23
subsys/modem/modem_cmux.c
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@ -221,7 +221,7 @@ static uint16_t modem_cmux_transmit_frame(struct modem_cmux *cmux,
uint16_t buf_idx;
space = ring_buf_space_get(&cmux->transmit_rb) - MODEM_CMUX_FRAME_SIZE_MAX;
data_len = (space < frame->data_len) ? space : frame->data_len;
data_len = MIN(space, frame->data_len);
/* SOF */
buf[0] = 0xF9;
@ -750,28 +750,27 @@ static void modem_cmux_process_received_byte(struct modem_cmux *cmux, uint8_t by
case MODEM_CMUX_RECEIVE_STATE_DATA:
/* Copy byte to data */
cmux->receive_buf[cmux->receive_buf_len] = byte;
if (cmux->receive_buf_len < cmux->receive_buf_size) {
cmux->receive_buf[cmux->receive_buf_len] = byte;
}
cmux->receive_buf_len++;
/* Check if datalen reached */
if (cmux->frame.data_len == cmux->receive_buf_len) {
/* Await FCS */
cmux->receive_state = MODEM_CMUX_RECEIVE_STATE_FCS;
break;
}
/* Check if receive buffer overrun */
if (cmux->receive_buf_len == cmux->receive_buf_size) {
LOG_WRN("Receive buf overrun");
/* Drop frame */
cmux->receive_state = MODEM_CMUX_RECEIVE_STATE_EOF;
break;
}
break;
case MODEM_CMUX_RECEIVE_STATE_FCS:
if (cmux->receive_buf_len > cmux->receive_buf_size) {
LOG_WRN("Receive buffer overrun (%u > %u)",
cmux->receive_buf_len, cmux->receive_buf_size);
cmux->receive_state = MODEM_CMUX_RECEIVE_STATE_DROP;
break;
}
/* Compute FCS */
if (cmux->frame.type == MODEM_CMUX_FRAME_TYPE_UIH) {
fcs = 0xFF - crc8(cmux->frame_header, cmux->frame_header_len,