app: PIPE interface to UART

Jira: SLM-134

Implement PIPE interface to Serial Modem UART to be able to use
the same UART implementation for both pure AT-commands and for
CMUXed AT-commands and PPP.

Signed-off-by: Markus Lassila <markus.lassila@nordicsemi.no>

Author: MarkusLassila

app/overlay-cmux.conf

@@ -11,18 +11,6 @@ CONFIG_SM_SKIP_READY_MSG=y
 CONFIG_MODEM_MODULES=y
 CONFIG_MODEM_CMUX=y
 
-# Enable Serial Modem UART backend
-CONFIG_MODEM_BACKEND_UART=n
-CONFIG_MODEM_BACKEND_UART_ASYNC=n
-CONFIG_MODEM_BACKEND_UART_SLM=y
-CONFIG_MODEM_BACKEND_UART_SLM_TRANSMIT_TIMEOUT_MS=1000
-
-# These buffers are unused after AT#CMUX is enabled
-# so use minimal buffer size
-CONFIG_SM_UART_RX_BUF_COUNT=2
-CONFIG_SM_UART_RX_BUF_SIZE=128
-CONFIG_SM_UART_TX_BUF_SIZE=128
-
 # debug options
 #CONFIG_MODEM_CMUX_LOG_LEVEL_DBG=y
 #CONFIG_MODEM_MODULES_LOG_LEVEL_DBG=y

app/overlay-ppp-cmux-linux.conf

@@ -11,25 +11,12 @@ CONFIG_SM_CR_TERMINATION=y
 
 CONFIG_MODEM_CMUX_MTU=127
 CONFIG_MODEM_CMUX_WORK_BUFFER_SIZE=536
-CONFIG_SM_CMUX_UART_BUFFER_SIZE=600
 
-# Enable Serial Modem UART backend
-CONFIG_MODEM_BACKEND_UART=n
-CONFIG_MODEM_BACKEND_UART_ASYNC=n
-CONFIG_MODEM_BACKEND_UART_SLM=y
-
-# For sending full 600 bytes at 115200 baudrate
-# 600 * 10 / 115200 = 52.1 ms
-CONFIG_MODEM_BACKEND_UART_SLM_TRANSMIT_TIMEOUT_MS=53
-# Assume at least baudrate 115200 for UART
-# so CMUX frame can be received in 12 ms (134*10/115200)
-CONFIG_MODEM_BACKEND_UART_SLM_RECEIVE_IDLE_TIMEOUT_MS=12
-
-# These buffers are unused after AT#CMUX is enabled
-# so use minimal buffer size
-CONFIG_SM_UART_RX_BUF_COUNT=2
-CONFIG_SM_UART_RX_BUF_SIZE=128
-CONFIG_SM_UART_TX_BUF_SIZE=128
+# With CMUX, the UART buffers should be at least the size of the
+# CONFIG_MODEM_CMUX_WORK_BUFFER_SIZE
+CONFIG_SM_UART_RX_BUF_COUNT=3
+CONFIG_SM_UART_RX_BUF_SIZE=256
+CONFIG_SM_UART_TX_BUF_SIZE=768
 
 # When using PPP, disable commands of IP-based protocols to save flash space.
 CONFIG_SM_FTPC=n

app/overlay-ppp-without-cmux.conf

@@ -0,0 +1,8 @@
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+
+# Enable modem UART backend
+CONFIG_MODEM_BACKEND_UART=y
+CONFIG_MODEM_BACKEND_UART_ASYNC=y

app/overlay-ppp.conf

@@ -24,12 +24,6 @@ CONFIG_NET_L2_PPP=y
 CONFIG_MODEM_MODULES=y
 CONFIG_MODEM_PPP=y
 
-# Enable Serial Modem UART backend
-CONFIG_MODEM_BACKEND_UART=n
-CONFIG_MODEM_BACKEND_UART_ASYNC=n
-CONFIG_MODEM_BACKEND_UART_SLM=y
-CONFIG_MODEM_BACKEND_UART_SLM_TRANSMIT_TIMEOUT_MS=1000
-
 # L2 protocol
 CONFIG_NET_L2_PPP_MGMT=y
 CONFIG_NET_L2_PPP_OPTION_MRU=y

app/prj.conf

@@ -133,6 +133,7 @@ CONFIG_SM_EXTERNAL_XTAL=n
 #CONFIG_SM_LOG_LEVEL_DBG=y
 #CONFIG_LOG_PRINTK=n
 #CONFIG_LOG_MODE_IMMEDIATE=y
+#CONFIG_DEBUG_OPTIMIZATIONS=y
 
 # For using external GNSS antenna
 #CONFIG_MODEM_ANTENNA=y

app/sample.yaml

@@ -85,6 +85,7 @@ tests:
     build_only: true
     extra_args:
       - EXTRA_CONF_FILE="overlay-ppp.conf"
+      - EXTRA_CONF_FILE="overlay-ppp-without-cmux.conf"
       - EXTRA_DTC_OVERLAY_FILE="overlay-ppp-without-cmux.overlay"
     platform_allow:
       - nrf9160dk/nrf9160/ns
@@ -104,6 +105,7 @@ tests:
     build_only: true
     extra_args:
       - EXTRA_CONF_FILE="overlay-ppp.conf"
+      - EXTRA_CONF_FILE="overlay-ppp-without-cmux.conf"
       - EXTRA_DTC_OVERLAY_FILE="overlay-ppp-without-cmux.overlay"
     extra_configs:
       - CONFIG_SM_POWER_PIN=31

app/src/sm_at_commands.c

@@ -383,34 +383,34 @@ int sm_at_init(void)
 
 	err = sm_at_tcp_proxy_init();
 	if (err) {
-		LOG_ERR("TCP Server could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "TCP Server", err);
 		return -EFAULT;
 	}
 	err = sm_at_udp_proxy_init();
 	if (err) {
-		LOG_ERR("UDP Server could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "UDP Server", err);
 		return -EFAULT;
 	}
 	err = sm_at_socket_init();
 	if (err) {
-		LOG_ERR("TCPIP could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "Socket", err);
 		return -EFAULT;
 	}
 	err = sm_at_icmp_init();
 	if (err) {
-		LOG_ERR("ICMP could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "ICMP", err);
 		return -EFAULT;
 	}
 #if defined(CONFIG_SM_SMS)
 	err = sm_at_sms_init();
 	if (err) {
-		LOG_ERR("SMS could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "SMS", err);
 		return -EFAULT;
 	}
 #endif
 	err = sm_at_fota_init();
 	if (err) {
-		LOG_ERR("FOTA could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "FOTA", err);
 		return -EFAULT;
 	}
 #if defined(CONFIG_SM_NRF_CLOUD)
@@ -419,63 +419,63 @@ int sm_at_init(void)
 		/* Allow nRF Cloud initialization to fail as sometimes JWT is missing
 		 * especially during development.
 		 */
-		LOG_ERR("nRF Cloud could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "nRF Cloud", err);
 		err = 0;
 	}
 #endif
 #if defined(CONFIG_SM_GNSS)
 	err = sm_at_gnss_init();
 	if (err) {
-		LOG_ERR("GNSS could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "GNSS", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_SM_FTPC)
 	err = sm_at_ftp_init();
 	if (err) {
-		LOG_ERR("FTP could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "FTP", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_SM_MQTTC)
 	err = sm_at_mqtt_init();
 	if (err) {
-		LOG_ERR("MQTT could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "MQTT", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_SM_HTTPC)
 	err = sm_at_httpc_init();
 	if (err) {
-		LOG_ERR("HTTP could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "HTTP", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_SM_GPIO)
 	err = sm_at_gpio_init();
 	if (err) {
-		LOG_ERR("GPIO could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "GPIO", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_SM_TWI)
 	err = sm_at_twi_init();
 	if (err) {
-		LOG_ERR("TWI could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "TWI", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_SM_CARRIER)
 	err = sm_at_carrier_init();
 	if (err) {
-		LOG_ERR("LwM2M carrier could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "LwM2M carrier", err);
 		return -EFAULT;
 	}
 #endif
 #if defined(CONFIG_LWM2M_CARRIER_SETTINGS)
 	err = sm_at_carrier_cfg_init();
 	if (err) {
-		LOG_ERR("LwM2M carrier could not be initialized: %d", err);
+		LOG_ERR("%s initialization failed (%d).", "LwM2M carrier", err);
 		return -EFAULT;
 	}
 #endif
@@ -485,7 +485,7 @@ int sm_at_init(void)
 #if defined(CONFIG_SM_PPP)
 	err = sm_ppp_init();
 	if (err) {
-		LOG_ERR("PPP initialization failed. (%d)", err);
+		LOG_ERR("%s initialization failed (%d).", "PPP", err);
 		return err;
 	}
 #endif
@@ -498,76 +498,79 @@ void sm_at_uninit(void)
 
 	err = sm_at_tcp_proxy_uninit();
 	if (err) {
-		LOG_WRN("TCP Server could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "TCP Server", err);
 	}
 	err = sm_at_udp_proxy_uninit();
 	if (err) {
-		LOG_WRN("UDP Server could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "UDP Server", err);
 	}
 	err = sm_at_socket_uninit();
 	if (err) {
-		LOG_WRN("TCPIP could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "Socket", err);
 	}
 	err = sm_at_icmp_uninit();
 	if (err) {
-		LOG_WRN("ICMP could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "ICMP", err);
 	}
 #if defined(CONFIG_SM_SMS)
 	err = sm_at_sms_uninit();
 	if (err) {
-		LOG_WRN("SMS could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "SMS", err);
 	}
 #endif
 	err = sm_at_fota_uninit();
 	if (err) {
-		LOG_WRN("FOTA could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "FOTA", err);
 	}
 #if defined(CONFIG_SM_NRF_CLOUD)
 	err = sm_at_nrfcloud_uninit();
 	if (err) {
-		LOG_WRN("nRF Cloud could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "nRF Cloud", err);
 	}
 #endif
 #if defined(CONFIG_SM_GNSS)
 	err = sm_at_gnss_uninit();
 	if (err) {
-		LOG_WRN("GNSS could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "GNSS", err);
 	}
 #endif
 #if defined(CONFIG_SM_FTPC)
 	err = sm_at_ftp_uninit();
 	if (err) {
-		LOG_WRN("FTP could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "FTP", err);
 	}
 #endif
 #if defined(CONFIG_SM_MQTTC)
 	err = sm_at_mqtt_uninit();
 	if (err) {
-		LOG_WRN("MQTT could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "MQTT", err);
 	}
 #endif
 #if defined(CONFIG_SM_HTTPC)
 	err = sm_at_httpc_uninit();
 	if (err) {
-		LOG_WRN("HTTP could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "HTTP", err);
 	}
 #endif
 #if defined(CONFIG_SM_TWI)
 	err = sm_at_twi_uninit();
 	if (err) {
-		LOG_ERR("TWI could not be uninit: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "TWI", err);
 	}
 #endif
 #if defined(CONFIG_SM_GPIO)
 	err = sm_at_gpio_uninit();
 	if (err) {
-		LOG_ERR("GPIO could not be uninit: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "GPIO", err);
 	}
 #endif
 #if defined(CONFIG_SM_CARRIER)
 	err = sm_at_carrier_uninit();
 	if (err) {
-		LOG_ERR("LwM2M carrier could not be uninitialized: %d", err);
+		LOG_WRN("%s uninitialization failed (%d).", "LwM2M carrier", err);
 	}
 #endif
+#if defined(CONFIG_SM_CMUX)
+	sm_cmux_uninit();
+#endif
 }