lib: modem_slm: Refactor UART implementation.

Rewrite of the previously unstable (freezes & lost data) UART
implementation between host device, which is using modem_slm lib,
and device with SLM.

Removed:
- CONFIG_MODEM_SLM_DMA_MAXLEN (RX buf size)
- modem_slm_reset_uart as there is no reason to reset UART.

Added Kconfigs for UART buffers:
- CONFIG_MODEM_SLM_UART_RX_BUF_COUNT
- CONFIG_MODEM_SLM_UART_RX_BUF_SIZE
- CONFIG_MODEM_SLM_UART_TX_BUF_SIZE

Added Kconfig for buffering AT-responses:
- CONFIG_MODEM_SLM_AT_CMD_RESP_MAX_SIZE

Signed-off-by: Markus Lassila <[email protected]>

Author: MarkusLassila

doc/nrf/libraries/modem/modem_slm.rst

@@ -32,14 +32,21 @@ The library is enabled and configured entirely using the Kconfig system.
 Configure the following Kconfig options to enable this library:
 
 * :kconfig:option:`CONFIG_MODEM_SLM` - Enables the Modem SLM library.
-* :kconfig:option:`CONFIG_MODEM_SLM_DMA_MAXLEN` - Configures UART RX EasyDMA buffer size, which is configured to 1024 bytes by default.
+* :kconfig:option:`CONFIG_MODEM_SLM_AT_CMD_RESP_MAX_SIZE` - Configures the size of the AT command response buffer.
+  The default size is 2100 bytes, which is aligned with SLM.
 * :kconfig:option:`CONFIG_MODEM_SLM_POWER_PIN` - Configures the mandatory power pin GPIO, which is not configured by default.
 * :kconfig:option:`CONFIG_MODEM_SLM_POWER_PIN_TIME` - Sets the toggle time value in milliseconds for power pin GPIO, by default 100 ms.
 
 Optionally configure the following Kconfig options based on need:
 
 * :kconfig:option:`CONFIG_MODEM_SLM_SHELL` - Enables the shell function in the Modem SLM library, which is not enabled by default.
 * :kconfig:option:`CONFIG_MODEM_SLM_INDICATE_PIN` - Configures the optional indicator GPIO, which is not configured by default.
+* :kconfig:option:`CONFIG_MODEM_SLM_UART_RX_BUF_COUNT` - Configures the number of RX buffers for the UART device.
+  The default value is 3.
+* :kconfig:option:`CONFIG_MODEM_SLM_UART_RX_BUF_SIZE` - Configures the size of the RX buffer for the UART device.
+  The default value is 256 bytes.
+* :kconfig:option:`CONFIG_MODEM_SLM_UART_TX_BUF_SIZE` - Configures the size of the TX buffer for the UART device.
+  The default value is 256 bytes.
 
 The application must use Zephyr ``chosen`` nodes in devicetree to select UART device.
 Additionally, GPIO can also be selected.
@@ -116,8 +123,6 @@ The SLM Monitor has similar functions to the :ref:`at_monitor_readme` library, e
 
      SLM_MONITOR(network, "\r\n+CEREG:", cereg_mon);
 
-     SLM_MONITOR(download, "\r\n#XDFUGET: 0,", download_mon, MON_PAUSED);
-
 API documentation
 *****************
 

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -459,6 +459,23 @@ Modem libraries
     Even within the same network, the PDN connection establishment method (PCO vs ePCO) might change when the device operates in NB-IoT or LTE Cat-M1, resulting in missing DNS addresses when one method is used, but not the other.
     Having a fallback DNS address ensures that the device always has a DNS to fallback to.
 
+* :ref:`lib_modem_slm` library:
+
+  * Added:
+
+      * The :kconfig:option:`CONFIG_MODEM_SLM_UART_RX_BUF_COUNT` Kconfig option for configuring RX buffer count.
+      * The :kconfig:option:`CONFIG_MODEM_SLM_UART_RX_BUF_SIZE` Kconfig option for configuring RX buffer size.
+      * The :kconfig:option:`CONFIG_MODEM_SLM_UART_TX_BUF_SIZE` Kconfig option for configuring TX buffer size.
+      * The :kconfig:option:`CONFIG_MODEM_SLM_AT_CMD_RESP_MAX_SIZE` Kconfig option for buffering AT command responses.
+
+  * Updated the UART implementation between the host device, using the :ref:`lib_modem_slm` library, and the device running the :ref:`Serial LTE Modem <slm_description>` application.
+
+  * Removed:
+
+      * The ``CONFIG_MODEM_SLM_DMA_MAXLEN`` Kconfig option.
+        Use :kconfig:option:`CONFIG_MODEM_SLM_UART_RX_BUF_SIZE` instead.
+      * The ``modem_slm_reset_uart`` function as there is no longer need to reset the UART.
+
 Multiprotocol Service Layer libraries
 -------------------------------------
 

include/modem/modem_slm.h

@@ -98,12 +98,6 @@ int modem_slm_register_ind(slm_ind_handler_t handler, bool wakeup);
  */
 int modem_slm_power_pin_toggle(void);
 
-/**
- * @brief Reset the RX function of the serial interface
- *
- */
-void modem_slm_reset_uart(void);
-
 /**
  * @brief Function to send an AT command in SLM command mode
  *

lib/modem_slm/Kconfig

@@ -9,16 +9,42 @@ menuconfig MODEM_SLM
 	depends on UART_ASYNC_API
 	depends on RING_BUFFER
 	select EXPERIMENTAL
+	select UART_USE_RUNTIME_CONFIGURE
 	bool "Modem SLM Library for MCU [EXPERIMENTAL]"
 
 if MODEM_SLM
 
-config MODEM_SLM_DMA_MAXLEN
-	int "Buffer size for UART RX EasyDMA"
-	range 256 2048
-	default 1024
+#
+# UART buffers
+#
+config MODEM_SLM_UART_RX_BUF_COUNT
+	int "Receive buffers for UART"
+	range 2 4
+	default 3
+	help
+	  Number of buffers for receiving (RX) UART traffic.
+	  If the buffers are full, UART RX will be disabled until the buffers are processed.
+
+config MODEM_SLM_UART_RX_BUF_SIZE
+	int "Receive buffer size for UART"
+	range 16 4096
+	default 256
+	help
+	  Amount of received (RX), unprocessed, UART traffic that can be held by a single buffer.
+
+config MODEM_SLM_UART_TX_BUF_SIZE
+	int "Send buffer size for UART"
+	range 16 4096
+	default 256
+	help
+	  Amount of UART traffic waiting to be sent (TX), which can be held.
+	  If the buffers are full, all messages will be sent synchronously.
+
+config MODEM_SLM_AT_CMD_RESP_MAX_SIZE
+	int "Maximum size of AT command response from SLM"
+	default 2100
 	help
-	  The maximum number of bytes in receive buffer.
+	  The maximum size of the AT command response.
 
 config MODEM_SLM_SHELL
 	bool "SLM Shell"