application: serial_lte_modem: integrate CMUX with PPP

The UART-based PPP driver is replaced by the PPP module of the modem subsystem. When both CMUX and PPP are enabled, CMUX automatically configures a second channel for PPP which can only be used through it. Thus, CMUX should be started before PPP, which means before activating LTE as PPP starts automatically when the LTE link goes up. However, SLM tolerates that CMUX is started only after LTE and PPP are up. As of now, upstream Zephyr commits are needed for this to work properly. Signed-off-by: Tomi Fontanilles <[email protected]>
gWacey · Feb 7, 2024 · 5458ab1 · 5458ab1
1 parent 88fbaa7
commit 5458ab1
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Showing 8 changed files with 195 additions and 87 deletions.
diff --git a/...ions/serial_lte_modem/overlay-ppp.overlay → ...te_modem/overlay-ppp-without-cmux.overlay b/...ions/serial_lte_modem/overlay-ppp.overlay → ...te_modem/overlay-ppp-without-cmux.overlay
@@ -4,9 +4,11 @@
  * SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
  */
 
+/* Include this overlay only if using PPP without CMUX. */
+
  / {
 	chosen {
-		zephyr,ppp-uart = &uart1;
+		ncs,slm-ppp-uart = &uart1;
 	};
 };
 

diff --git a/applications/serial_lte_modem/overlay-ppp.conf b/applications/serial_lte_modem/overlay-ppp.conf
@@ -28,8 +28,11 @@ CONFIG_TFM_SECURE_UART_SHARE_INSTANCE=y
 # Zephyr PPP support
 CONFIG_NET_NATIVE=y
 CONFIG_NET_L2_PPP=y
-CONFIG_NET_DRIVERS=y
-CONFIG_NET_PPP=y
+CONFIG_MODEM_MODULES=y
+CONFIG_MODEM_PPP=y
+CONFIG_MODEM_BACKEND_UART=y
+# Allow large UART TXs to go through @115200.
+CONFIG_MODEM_BACKEND_UART_ASYNC_TRANSMIT_TIMEOUT_MS=400
 
 # L2 protocol
 CONFIG_NET_L2_PPP_MGMT=y
@@ -39,16 +42,6 @@ CONFIG_NET_L2_PPP_OPTION_SERVE_DNS=y
 CONFIG_NET_L2_PPP_TIMEOUT=5000
 CONFIG_NET_L2_PPP_MAX_CONFIGURE_REQ_RETRANSMITS=20
 
-# UART driver
-CONFIG_NET_PPP_ASYNC_UART=y
-CONFIG_NET_PPP_UART_BUF_LEN=2048
-CONFIG_NET_PPP_ASYNC_UART_TX_BUF_LEN=4096
-CONFIG_NET_PPP_RINGBUF_SIZE=4096
-CONFIG_NET_PPP_RX_STACK_SIZE=2048
-CONFIG_NET_PPP_VERIFY_FCS=n
-CONFIG_PPP_CLIENT_CLIENTSERVER=y # Windows support
-CONFIG_PPP_NET_IF_NO_AUTO_START=y
-
 # IP stack
 CONFIG_NET_IPV4=y
 CONFIG_NET_IPV6=y
@@ -66,9 +59,9 @@ CONFIG_NET_TC_RX_COUNT=0
 
 # debug options
 #CONFIG_LOG_PROCESS_THREAD_STACK_SIZE=4096
-#CONFIG_LOG_DEFAULT_LEVEL=4
 #CONFIG_NET_LOG=y
 #CONFIG_NET_PKT_LOG_LEVEL_DBG=y
-#CONFIG_NET_PPP_LOG_LEVEL_DBG=y
 #CONFIG_NET_L2_PPP_LOG_LEVEL_DBG=y
+#CONFIG_NET_MGMT_EVENT_LOG_LEVEL_DBG=y
+#CONFIG_MODEM_MODULES_LOG_LEVEL_DBG=y
 #CONFIG_UART_LOG_LEVEL_DBG=y
diff --git a/applications/serial_lte_modem/prj.conf b/applications/serial_lte_modem/prj.conf
@@ -110,7 +110,8 @@ CONFIG_SLM_EXTERNAL_XTAL=n
 CONFIG_SLM_START_SLEEP=n
 CONFIG_SLM_DATAMODE_URC=n
 
-# Debug configurations
+# debug options
+#CONFIG_ASSERT=y
 #CONFIG_LOG_BUFFER_SIZE=16384
 #CONFIG_SLM_LOG_LEVEL_DBG=y
 #CONFIG_LOG_PRINTK=n

diff --git a/applications/serial_lte_modem/src/slm_at_commands.c b/applications/serial_lte_modem/src/slm_at_commands.c
@@ -669,7 +669,16 @@ int slm_at_init(void)
 		return -EFAULT;
 	}
 #endif
-
+#if defined(CONFIG_SLM_CMUX)
+	slm_cmux_init();
+#endif
+#if defined(CONFIG_SLM_PPP)
+	err = slm_ppp_init();
+	if (err) {
+		LOG_ERR("PPP initialization failed. (%d)", err);
+		return err;
+	}
+#endif
 	return err;
 }
 

diff --git a/applications/serial_lte_modem/src/slm_at_host.c b/applications/serial_lte_modem/src/slm_at_host.c
@@ -892,14 +892,6 @@ int slm_at_host_init(void)
 		return -EFAULT;
 	}
 
-#if defined(CONFIG_SLM_PPP)
-	err = slm_ppp_init();
-	if (err) {
-		LOG_ERR("PPP initialization failed (%d).", err);
-		return err;
-	}
-#endif
-
 	k_work_init(&raw_send_scheduled_work, raw_send_scheduled);
 
 	err = slm_uart_handler_enable();

diff --git a/applications/serial_lte_modem/src/slm_cmux.c b/applications/serial_lte_modem/src/slm_cmux.c
@@ -16,6 +16,9 @@ LOG_MODULE_REGISTER(slm_cmux, CONFIG_SLM_LOG_LEVEL);
 
 enum cmux_channel {
 	AT_CHANNEL,
+#if defined(CONFIG_SLM_PPP)
+	PPP_CHANNEL,
+#endif
 	CHANNEL_COUNT
 };
 
@@ -77,8 +80,9 @@ static void dlci_pipe_event_handler(struct modem_pipe *pipe,
 
 static void cmux_event_handler(struct modem_cmux *, enum modem_cmux_event event, void *)
 {
-	assert(event == MODEM_CMUX_EVENT_CONNECTED || event == MODEM_CMUX_EVENT_DISCONNECTED);
-	LOG_INF("CMUX %sconnected.", (event == MODEM_CMUX_EVENT_CONNECTED) ? "" : "dis");
+	if (event == MODEM_CMUX_EVENT_CONNECTED || event == MODEM_CMUX_EVENT_DISCONNECTED) {
+		LOG_INF("CMUX %sconnected.", (event == MODEM_CMUX_EVENT_CONNECTED) ? "" : "dis");
+	}
 }
 
 static void init_dlci(size_t dlci_idx, uint16_t recv_buf_size,
@@ -151,6 +155,30 @@ static bool cmux_is_initialized(void)
 	return (cmux.uart_pipe != NULL);
 }
 
+void slm_cmux_init(void)
+{
+	const struct modem_cmux_config cmux_config = {
+		.callback = cmux_event_handler,
+		.receive_buf = cmux.cmux_receive_buf,
+		.receive_buf_size = sizeof(cmux.cmux_receive_buf),
+		.transmit_buf = cmux.cmux_transmit_buf,
+		.transmit_buf_size = sizeof(cmux.cmux_transmit_buf),
+	};
+
+	modem_cmux_init(&cmux.instance, &cmux_config);
+
+	for (size_t i = 0; i != ARRAY_SIZE(cmux.dlcis); ++i) {
+		init_dlci(i, sizeof(cmux.dlcis[i].receive_buf), cmux.dlcis[i].receive_buf);
+	}
+}
+
+#if defined(CONFIG_SLM_PPP)
+void *slm_cmux_get_ppp_channel_pipe(void)
+{
+	return cmux.dlcis[PPP_CHANNEL].pipe;
+}
+#endif
+
 static int cmux_start(void)
 {
 	int ret;
@@ -177,22 +205,6 @@ static int cmux_start(void)
 			return -ENODEV;
 		}
 	}
-	{
-		const struct modem_cmux_config cmux_config = {
-			.callback = cmux_event_handler,
-			.receive_buf = cmux.cmux_receive_buf,
-			.receive_buf_size = sizeof(cmux.cmux_receive_buf),
-			.transmit_buf = cmux.cmux_transmit_buf,
-			.transmit_buf_size = sizeof(cmux.cmux_transmit_buf),
-		};
-
-		modem_cmux_init(&cmux.instance, &cmux_config);
-	}
-	{
-		for (size_t i = 0; i != ARRAY_SIZE(cmux.dlcis); ++i) {
-			init_dlci(i, sizeof(cmux.dlcis[i].receive_buf), cmux.dlcis[i].receive_buf);
-		}
-	}
 
 	ret = modem_cmux_attach(&cmux.instance, cmux.uart_pipe);
 	if (ret) {

diff --git a/applications/serial_lte_modem/src/slm_cmux.h b/applications/serial_lte_modem/src/slm_cmux.h
@@ -8,6 +8,12 @@
 
 #include <modem/at_cmd_parser.h>
 
+void slm_cmux_init(void);
+
+#if defined(CONFIG_SLM_PPP)
+void *slm_cmux_get_ppp_channel_pipe(void);
+#endif
+
 int handle_at_cmux(enum at_cmd_type cmd_type);
 
 #endif