drivers: dtr_uart: Change RI from pulse to level

Previously RI lasted for 100ms or until DTR was activated,
now RI lasts until DTR is activated.

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

Author: MarkusLassila

doc/app/sm_configuration.rst

@@ -323,4 +323,4 @@ The following configuration files are provided:
   See the :ref:`SM_AT_FOTA` for more information.
 
 The board-specific devicetree overlays (:file:`boards/*.overlay`) set up configurations that are specific to each supported development kit.
-All of them configure the DTR to be deasserted from a button and RI to blink an LED.
+All of them configure the DTR to be deasserted from a button and RI to drive an LED.

doc/images/cmux-wakeup-timing.svg

@@ -66,7 +66,7 @@ The |SM| application uses DTR (Data Terminal Ready) and RI (Ring Indicator) pins
 * Added:
 
   * DTR pin, which is a level-based input that is configured in the devicetree with the ``dtr-gpios`` property.
-  * RI pin, which is a pulse-based output that is configured in the devicetree with the ``ri-gpios`` property.
+  * RI pin, which is a level-based output that is configured in the devicetree with the ``ri-gpios`` property.
 
 See :ref:`uart_configuration` for more information on how DTR and RI pins work in the |SM| application.
 See :ref:`sm_cellular_modem` for information on how to configure DTR and RI pins when using the |SM| application as a Zephyr modem.

doc/migration_notes.rst

@@ -263,16 +263,19 @@ No other GPIO control is required to utilize the PSM or eDRX modes.
 Incoming data wake-up
 =====================
 
-When the UART is powered down and there is incoming data, the |SM| application issues a pulse signal on the **RI** pin to notify the host.
+When the UART is powered down and there is incoming data, the |SM| application asserts the **RI** pin to notify the host.
 The RI signal is handled by the modem driver on the host, which powers up the UART device and asserts the DTR line, signaling the |SM| that the UART is powered on and ready to receive data.
+The RI signal remains asserted until the nRF91 UART is activated and ready to transmit data.
 
 .. figure:: images/cmux-wakeup-timing.svg
    :alt: Modem waking up the host timing diagram
 
    Sequence diagram showing the wake-up sequence when the UART is powered down
 
 This sequence diagram illustrates the wake-up sequence when the UART is powered down.
-The RI signal pulse triggers the host to power up its UART and assert DTR, which in turn signals the modem that the UART interface is ready.
+The RI signal triggers the host to power up its UART and assert DTR.
+Once the host UART is ready and DTR is asserted, the nRF91 enables its UART interface.
+The RI signal remains active throughout this process and only returns to inactive once the nRF91 UART is active.
 This coordinated wake-up ensures both ends of the communication link are ready before data transmission begins.
 
 Host-initiated wake-up

doc/uart_configuration.rst

@@ -50,7 +50,7 @@ struct dtr_uart_data {
 	struct k_work_delayable dtr_work;
 
 	/* --- RI (Ring Indicator) --- */
-	struct k_work_delayable ri_work;
+	bool ri_active;	/* RI signal currently active */
 
 	/* --- Power Management --- */
 	bool pm_suspended;	/* 0 = UART && DTR active, 1 = UART && DTR inactive */
@@ -206,26 +206,24 @@ static void activate_rx(struct dtr_uart_data *data)
 	user_callback(data->dev, &evt);
 }
 
-/* --- RI handling --- */
-static void ri_work_fn(struct k_work *work)
+static void ri_start(struct dtr_uart_data *data)
 {
-	const struct k_work_delayable *delayed_work =
-		CONTAINER_OF(work, struct k_work_delayable, work);
-	const struct dtr_uart_data *data =
-		CONTAINER_OF(delayed_work, struct dtr_uart_data, ri_work);
 	const struct dtr_uart_config *config = data->dev->config;
 
-	LOG_INF("RI: Stop");
-	gpio_pin_set_dt(&config->ri_gpio, 0);
+	LOG_INF("RI: Start");
+	gpio_pin_set_dt(&config->ri_gpio, 1);
+	data->ri_active = true;
 }
 
-static void ri_start(struct dtr_uart_data *data)
+static void ri_stop(struct dtr_uart_data *data)
 {
 	const struct dtr_uart_config *config = data->dev->config;
 
-	LOG_INF("RI: Start");
-	gpio_pin_set_dt(&config->ri_gpio, 1);
-	k_work_schedule(&data->ri_work, K_MSEC(100));
+	if (data->ri_active) {
+		LOG_INF("RI: Stop");
+		gpio_pin_set_dt(&config->ri_gpio, 0);
+		data->ri_active = false;
+	}
 }
 
 /* --- DTR handling --- */
@@ -256,14 +254,13 @@ static void dtr_work_handler(struct k_work *work)
 	data->dtr_state = asserted;
 
 	if (asserted) {
-		/* Stop RI signal. */
-		k_work_cancel_delayable(&data->ri_work);
-		gpio_pin_set_dt(&config->ri_gpio, 0);
-
 		/* Enable UART and RX/TX. */
 		power_on_uart(data);
 		activate_rx(data);
 		activate_tx(data);
+
+		/* Stop RI signal. */
+		ri_stop(data);
 	} else {
 		/* Disable TX. */
 		deactivate_tx(data);
@@ -382,7 +379,7 @@ static int api_tx(const struct device *dev, const uint8_t *buf, size_t len, int3
 	data->tx_buf = buf;
 	data->tx_len = len;
 
-	/* Start RI pulse. */
+	/* Start RI signal. */
 	ri_start(data);
 
 	/* Buffer the data until DTR is down. */
@@ -580,7 +577,6 @@ static int dtr_uart_init(const struct device *dev)
 	k_mutex_init(&data->dtr_mutex);
 	k_sem_init(&data->rx_disable_sync, 0, 1);
 	k_work_init_delayable(&data->dtr_work, dtr_work_handler);
-	k_work_init_delayable(&data->ri_work, ri_work_fn);
 
 	/* Set UART callback. */
 	err = uart_callback_set(config->uart, uart_callback, (void *)dev);