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modem: cmux: Implement DM and NSC responses #96626

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merged 1 commit into from
Oct 9, 2025
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modem: cmux: Implement DM and NSC responses #96626

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79 changes: 73 additions & 6 deletions subsys/modem/modem_cmux.c
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Original file line number Diff line number Diff line change
Expand Up @@ -338,6 +338,7 @@ static bool modem_cmux_transmit_cmd_frame(struct modem_cmux *cmux,

if (space < MODEM_CMUX_CMD_FRAME_SIZE_MAX) {
k_mutex_unlock(&cmux->transmit_rb_lock);
LOG_WRN("CMD buffer overflow");
return false;
}

Expand Down Expand Up @@ -475,6 +476,41 @@ static void modem_cmux_on_control_frame_ua(struct modem_cmux *cmux)
k_event_post(&cmux->event, MODEM_CMUX_EVENT_CONNECTED_BIT);
}

static void modem_cmux_respond_unsupported_cmd(struct modem_cmux *cmux)
{
struct modem_cmux_frame frame = cmux->frame;
struct modem_cmux_command *cmd;

if (modem_cmux_wrap_command(&cmd, frame.data, frame.data_len) < 0) {
LOG_WRN("Invalid command");
return;
}

struct {
/* 3GPP TS 27.010: 5.4.6.3.8 Non Supported Command Response (NSC) */
struct modem_cmux_command nsc;
struct modem_cmux_command_type value;
} nsc_cmd = {
.nsc = {
.type = {
.ea = 1,
.cr = 0,
.value = MODEM_CMUX_COMMAND_NSC,
},
.length = {
.ea = 1,
.value = 1,
},
},
.value = cmd->type,
};

frame.data = (uint8_t *)&nsc_cmd;
frame.data_len = sizeof(nsc_cmd);

modem_cmux_transmit_cmd_frame(cmux, &frame);
}

static void modem_cmux_on_control_frame_uih(struct modem_cmux *cmux)
{
struct modem_cmux_command *command;
Expand Down Expand Up @@ -511,6 +547,7 @@ static void modem_cmux_on_control_frame_uih(struct modem_cmux *cmux)

default:
LOG_DBG("Unknown control command");
modem_cmux_respond_unsupported_cmd(cmux);
break;
}
}
Expand All @@ -534,6 +571,26 @@ static void modem_cmux_connect_response_transmit(struct modem_cmux *cmux)
modem_cmux_transmit_cmd_frame(cmux, &frame);
}

static void modem_cmux_dm_response_transmit(struct modem_cmux *cmux)
{
if (cmux == NULL) {
return;
}

/* 3GPP TS 27.010: 5.3.3 Disconnected Mode (DM) response */
struct modem_cmux_frame frame = {
.dlci_address = cmux->frame.dlci_address,
.cr = cmux->frame.cr,
.pf = 1,
.type = MODEM_CMUX_FRAME_TYPE_DM,
.data = NULL,
.data_len = 0,
};

LOG_DBG("Send DM response");
modem_cmux_transmit_cmd_frame(cmux, &frame);
}

static void modem_cmux_on_control_frame_sabm(struct modem_cmux *cmux)
{
modem_cmux_connect_response_transmit(cmux);
Expand Down Expand Up @@ -593,6 +650,13 @@ static struct modem_cmux_dlci *modem_cmux_find_dlci(struct modem_cmux *cmux)
return NULL;
}

static void modem_cmux_on_dlci_frame_dm(struct modem_cmux_dlci *dlci)
{
dlci->state = MODEM_CMUX_DLCI_STATE_CLOSED;
modem_pipe_notify_closed(&dlci->pipe);
k_work_cancel_delayable(&dlci->close_work);
}

static void modem_cmux_on_dlci_frame_ua(struct modem_cmux_dlci *dlci)
{
switch (dlci->state) {
Expand All @@ -608,9 +672,7 @@ static void modem_cmux_on_dlci_frame_ua(struct modem_cmux_dlci *dlci)

case MODEM_CMUX_DLCI_STATE_CLOSING:
LOG_DBG("DLCI %u closed", dlci->dlci_address);
dlci->state = MODEM_CMUX_DLCI_STATE_CLOSED;
modem_pipe_notify_closed(&dlci->pipe);
k_work_cancel_delayable(&dlci->close_work);
modem_cmux_on_dlci_frame_dm(dlci);
break;

default:
Expand All @@ -619,6 +681,8 @@ static void modem_cmux_on_dlci_frame_ua(struct modem_cmux_dlci *dlci)
}
}



static void modem_cmux_on_dlci_frame_uih(struct modem_cmux_dlci *dlci)
{
struct modem_cmux *cmux = dlci->cmux;
Expand Down Expand Up @@ -665,7 +729,7 @@ static void modem_cmux_on_dlci_frame_disc(struct modem_cmux_dlci *dlci)
modem_cmux_connect_response_transmit(cmux);

if (dlci->state != MODEM_CMUX_DLCI_STATE_OPEN) {
LOG_DBG("Unexpected Disc frame");
modem_cmux_dm_response_transmit(cmux);
return;
}

Expand All @@ -682,8 +746,9 @@ static void modem_cmux_on_dlci_frame(struct modem_cmux *cmux)

dlci = modem_cmux_find_dlci(cmux);
if (dlci == NULL) {
LOG_WRN("Ignoring frame intended for unconfigured DLCI %u.",
LOG_WRN("Frame intended for unconfigured DLCI %u.",
cmux->frame.dlci_address);
modem_cmux_dm_response_transmit(cmux);
return;
}

Expand All @@ -703,7 +768,9 @@ static void modem_cmux_on_dlci_frame(struct modem_cmux *cmux)
case MODEM_CMUX_FRAME_TYPE_DISC:
modem_cmux_on_dlci_frame_disc(dlci);
break;

case MODEM_CMUX_FRAME_TYPE_DM:
modem_cmux_on_dlci_frame_dm(dlci);
break;
default:
LOG_WRN("Unknown %s frame type (%d, DLCI %d)", "DLCI", cmux->frame.type,
cmux->frame.dlci_address);
Expand Down