app: Add support for AT+IPR to change baud rate

Add V.250 command AT+IPR=<baud> for changing the fixed baud rate.

Update the linux dial-up script to utilize the AT+IPR.

Signed-off-by: Seppo Takalo <seppo.takalo@nordicsemi.no>

Author: SeppoTakalo

app/scripts/sm_start_ppp.sh

@@ -25,6 +25,7 @@
 #
 MODEM=/dev/ttyACM0
 BAUD=115200
+IPR_BAUD=0
 TIMEOUT=60
 APN="internet"
 TYPE="IPV4V6"
@@ -39,11 +40,15 @@ TRACE_PID_FILE="/var/run/nrf91-modem-trace.pid"
 TRACE=0
 
 usage() {
-    echo "Usage: $0 [-s serial_port] [-b baud_rate] [-t timeout] [-a APN] [-f IP|IPV6|IPV4V6] \
-[-p PDN] [-T] [-v] [-h]"
+    echo "Usage: $0 [-s serial_port] [-b baud_rate] [-B new_speed] [-t timeout] [-a APN]"
+    echo "          [-f IP|IPV6|IPV4V6] [-p PDN] [-T] [-v] [-h]"
     echo ""
     echo "  -s serial_port : Serial port where the modem is connected (default: $MODEM)"
-    echo "  -b baud_rate   : Baud rate for serial communication (default: $BAUD)"
+    echo "  -b baud_rate   : Current baud rate of Serial Modem (default: $BAUD)"
+    echo "  -B new_speed   : Use AT+IPR to change baud rate to <new_speed>"
+    echo "                   Start with current baud rate and switch to new_speed after modem is"
+    echo "                   responsive. If not set, baud rate will not be changed."
+    echo "                   When terminated, baud rate will be switched back to original."
     echo "  -t timeout     : Timeout for dialup commands in seconds (default: $TIMEOUT)"
     echo "  -a APN         : Access Point Name for cellular connection (default: $APN)"
     echo "  -f FAMILY      : PDP_type, one of IP, IPV6, IPV4V6 (default: $TYPE)"
@@ -56,11 +61,12 @@ usage() {
 }
 
 # Parse command line parameters
-while getopts s:b:t:a::f:p:Thv flag
+while getopts s:b:B:t:a::f:p:Thv flag
 do
     case "${flag}" in
 	s) MODEM=${OPTARG};;
 	b) BAUD=${OPTARG};;
+	B) IPR_BAUD=${OPTARG};;
 	t) TIMEOUT=${OPTARG};;
 	a) APN=${OPTARG};;
 	p) PDN=${OPTARG};;
@@ -199,6 +205,13 @@ else
 	cmux_close
 fi
 
+if [ $IPR_BAUD -ne 0 ]; then
+	log_dbg "Set baud rate on modem to $IPR_BAUD"
+	chat $CHATOPT -t1 '' "AT+IPR=$IPR_BAUD" "OK" >$MODEM <$MODEM
+	# Reconfigure serial port
+	stty -F $MODEM $IPR_BAUD pass8 raw crtscts clocal
+fi
+
 log_dbg "Attach CMUX channel to modem..."
 ldattach -c $'\rAT#XCMUX=1\r' GSM0710 $MODEM
 
@@ -235,6 +248,11 @@ shutdown_modem() {
 		cmux_close
 		chat $CHATOPT -t5 '' $SHUTDOWN_SCRIPT >$MODEM <$MODEM
 	fi
+	if [ $IPR_BAUD -ne 0 ]; then
+		# Restore baud rate on modem
+		chat $CHATOPT -t1 '' "AT+IPR=$BAUD" "OK" >$MODEM <$MODEM
+		stty -F $MODEM $BAUD
+	fi
 }
 
 ppp_start() {
@@ -259,6 +277,8 @@ export SHUTDOWN_SCRIPT
 export PPP_OPTIONS
 export PIDFILE
 export CHATOPT
+export BAUD
+export IPR_BAUD
 export TRACE_PID_FILE
 export -f ppp_start
 export -f shutdown_modem

app/src/sm_at_commands.c

@@ -303,10 +303,12 @@ STATIC int handle_at_clac(enum at_parser_cmd_type cmd_type, struct at_parser *,
 	rsp_send("\r\n");
 	for (size_t i = 0; i < cmd_custom_count; i++) {
 		const char *cmd = _nrf_modem_at_cmd_custom_list_start[i].cmd;
-		/* Modem AT comamands start with 'AT+' or AT%. Other commands are
+		/* Modem AT commands start with 'AT+' or AT%. Other commands are
 		 * Serial Modem specific'. Skip modem AT commands.
+		 * Exception: AT+IPR is implemented in Serial Modem.
 		 */
-		if (strncasecmp(cmd, "AT+", strlen("AT+")) == 0 ||
+		if ((strncasecmp(cmd, "AT+", strlen("AT+")) == 0 &&
+		     strncasecmp(cmd, "AT+IPR", strlen("AT+IPR")) != 0) ||
 		    strncasecmp(cmd, "AT%%", strlen("AT%%")) == 0) {
 			continue;
 		}

app/src/sm_uart_handler.c

@@ -15,6 +15,7 @@
 #include "sm_uart_handler.h"
 #include "sm_at_host.h"
 #include "sm_util.h"
+#include "sm_cmux.h"
 
 #include <zephyr/logging/log.h>
 LOG_MODULE_REGISTER(sm_uart_handler, CONFIG_SM_LOG_LEVEL);
@@ -554,6 +555,66 @@ int sm_tx_write(const uint8_t *data, size_t len, bool flush, bool urc)
 	return sm_uart_tx_write(data, len, flush, urc);
 }
 
+SM_AT_CMD_CUSTOM(xppp, "AT+IPR", handle_at_ipr);
+static int handle_at_ipr(enum at_parser_cmd_type cmd_type, struct at_parser *parser,
+			 uint32_t param_count)
+{
+	int err;
+	struct uart_config cfg;
+
+	err = uart_config_get(sm_uart_dev, &cfg);
+	if (err) {
+		LOG_ERR("uart_config_get: %d", err);
+		return err;
+	}
+
+	if (cmd_type == AT_PARSER_CMD_TYPE_READ) {
+		rsp_send("\r\n+IPR: %u\r\n", cfg.baudrate);
+		return 0;
+	}
+
+	if (cmd_type == AT_PARSER_CMD_TYPE_TEST) {
+		rsp_send("\r\n+IPR: (),(%u,%u,%u,%u,%u)\r\n",
+			 115200, 230400, 460800, 921600, 1000000);
+		return 0;
+	}
+
+	if (cmd_type != AT_PARSER_CMD_TYPE_SET || param_count != 2) {
+		return -EINVAL;
+	}
+
+	if (sm_cmux_is_started()) {
+		LOG_ERR("Cannot change baudrate while CMUX is active.");
+		return -EBUSY;
+	}
+
+	err = at_parser_num_get(parser, 1, &cfg.baudrate);
+	if (err) {
+		return err;
+	}
+
+	if ((cfg.baudrate != 115200) &&
+	    (cfg.baudrate != 230400) &&
+	    (cfg.baudrate != 460800) &&
+	    (cfg.baudrate != 921600) &&
+	    (cfg.baudrate != 1000000)) {
+		LOG_ERR("Unsupported baudrate: %u", cfg.baudrate);
+		return -EINVAL;
+	}
+
+	rsp_send_ok();
+
+	sm_uart_handler_disable();
+	err = uart_configure(sm_uart_dev, &cfg);
+	if (err) {
+		LOG_ERR("uart_configure: %d", err);
+		return err;
+	}
+	sm_uart_handler_enable();
+
+	return -SILENT_AT_COMMAND_RET;
+}
+
 int sm_uart_handler_enable(void)
 {
 	int err;

doc/app/at_generic.rst

@@ -9,6 +9,98 @@ Generic AT commands
 
 This page describes generic AT commands.
 
+UART baud rate AT+IPR
+=====================
+
+The ``AT+IPR`` command sets the UART baud rate.
+
+Set command
+-----------
+
+The set command sets the UART baud rate.
+|SM| does not support automatic baud rate detection.
+When the device resets, the baud rate is set to the default value set in the devicetree.
+
+Syntax
+~~~~~~
+
+::
+
+   AT+IPR=<baud_rate>
+
+The ``<baud_rate>`` parameter is an integer value specifying the desired baud rate.
+
+.. note::
+
+   The baud rate change takes effect after the modem responds with ``OK``.
+   The host must switch to the new baud rate to continue communication.
+
+Example
+~~~~~~~
+
+Set the baud rate to 115200.
+
+::
+
+   AT+IPR=115200
+   OK
+
+Read command
+------------
+
+The read command reads the current UART baud rate.
+
+Syntax
+~~~~~~
+
+::
+
+   AT+IPR?
+
+Response syntax
+~~~~~~~~~~~~~~~
+
+::
+
+   +IPR: <baud_rate>
+
+Example
+~~~~~~~
+
+::
+
+   AT+IPR?
+   +IPR: 115200
+   OK
+
+Test command
+------------
+
+The test command lists the supported baud rates.
+
+Syntax
+~~~~~~
+
+::
+
+   AT+IPR=?
+
+Response syntax
+~~~~~~~~~~~~~~~
+
+::
+
+   +IPR: (list of supported autodetectable baud rates)[,(list of fixed-only baud rates)]
+
+Example
+~~~~~~~
+
+::
+
+   AT+IPR=?
+   +IPR: (),(115200,230400,460800,921600,1000000)
+   OK
+
 |SM| echo E0/E1
 ===============