drivers: add lpuarte driver and sample

Add low power uarte driver and sample.
Based on NCS LPUARTE driver and sample,
nrfconnect/sdk-nrf/commit/d33871cc92bc50034a6d9b7bdcac94c0ff358390

Signed-off-by: Eivind Jølsgard <[email protected]>

Author: eivindj-nordic

CODEOWNERS

@@ -34,6 +34,7 @@
 # Drivers
 /drivers/clock_control/                   @nrfconnect/ncs-bm
 /drivers/console/                         @nrfconnect/ncs-bm
+/drivers/lpuarte/                         @nrfconnect/ncs-bm
 
 # Include
 /include/*.h                              @nrfconnect/ncs-bm

boards/nordic/bm_nrf54l15dk/include/board-config.h

@@ -81,6 +81,30 @@ extern "C" {
 #define BOARD_APP_UARTE_PIN_CTS NRF_PIN_PORT_TO_PIN_NUMBER(3, 0)
 #endif
 
+/* Application LPUART configuration */
+#ifndef BOARD_APP_LPUARTE_INST
+#define BOARD_APP_LPUARTE_INST 21
+#endif
+
+#ifndef BOARD_APP_LPUARTE_PIN_TX
+#define BOARD_APP_LPUARTE_PIN_TX NRF_PIN_PORT_TO_PIN_NUMBER(11, 1)
+#endif
+#ifndef BOARD_APP_LPUARTE_PIN_RX
+#define BOARD_APP_LPUARTE_PIN_RX NRF_PIN_PORT_TO_PIN_NUMBER(10, 1)
+#endif
+#ifndef BOARD_APP_LPUARTE_PIN_RTS
+#define BOARD_APP_LPUARTE_PIN_RTS NRF_PIN_PORT_TO_PIN_NUMBER(14, 1)
+#endif
+#ifndef BOARD_APP_LPUARTE_PIN_CTS
+#define BOARD_APP_LPUARTE_PIN_CTS NRF_PIN_PORT_TO_PIN_NUMBER(13, 1)
+#endif
+#ifndef BOARD_APP_LPUARTE_PIN_REQ
+#define BOARD_APP_LPUARTE_PIN_REQ NRF_PIN_PORT_TO_PIN_NUMBER(8, 1)
+#endif
+#ifndef BOARD_APP_LPUARTE_PIN_RDY
+#define BOARD_APP_LPUARTE_PIN_RDY NRF_PIN_PORT_TO_PIN_NUMBER(9, 1)
+#endif
+
 #ifdef __cplusplus
 }
 #endif

doc/nrf-bm/drivers.rst

@@ -0,0 +1,17 @@
+.. _drivers:
+
+Drivers
+#######
+
+In supplement to nrfx drivers, |BMlong| provides drivers that implement typical use cases with Nordic Semiconductor devices.
+If the driver you are looking for is not available below, please check the nrfx documentation. TODO LINK.
+
+Only nrfx drivers and the drivers located under :file:`nrf-bm/drivers` are in the scope of the |BMshort| option.
+All other drivers that are included in the distribution must be ignored when working with the |BMshort| option.
+
+.. toctree::
+   :maxdepth: 2
+   :glob:
+   :caption: Subpages:
+
+   drivers/lpuarte.rst

doc/nrf-bm/drivers/lpuarte.rst

@@ -0,0 +1,49 @@
+.. _lpuarte:
+
+Low Power UART with EasyDMA (LPUARTE)
+#####################################
+
+The Low Power UART with EasyDMA (LPUARTE) driver implements the standard UART with two extra control lines for low power capabilities.
+The control lines allow for disabling the UART receiver during the idle period.
+This results in low power consumption, as you can shut down the high-frequency clock when UART is in idle state.
+
+Control protocol
+****************
+
+You can use the protocol for duplex transmission between two devices.
+
+The control protocol uses two additional lines alongside the standard TX and RX lines:
+
+* the *Request* line (REQ),
+* the *Ready* line (RDY).
+
+The REQ line of the first device is connected with the RDY line of the second device.
+It is configured as an output and set to low.
+
+The RDY line is configured as input without pull-up and the interrupt is configured to detect the transition from low to high state.
+
+The driver implements the control protocol in the following way:
+
+#. The transmitter initiates the transmission by calling :c:func:`bm_lpuarte_tx`.
+#. The driver reconfigures the REQ line to input with pull-up and enables the detection of high to low transition.
+#. The line is set to high due to the pull-up register, and that triggers an interrupt on the RDY line.
+#. On that interrupt, the driver starts the UART receiver.
+#. When the receiver is ready, the driver reconfigures the RDY line to output low.
+#. Then, the driver reconfigures the RDY line to input with pull-up and enables the interrupt on detection of high to low transition.
+#. This sequence results in a short pulse on the line, as the line goes low and high.
+#. The initiator detects the pulse and starts the standard UART transfer.
+#. When the transfer is completed, the driver reconfigures the REQ line to the initial state: output set to low.
+   This results in a line state change.
+#. As the line goes low, the receiver detects the change.
+   This indicates that the UARTE receiver can be stopped.
+
+Once the receiver acknowledges the transfer, it must be capable of receiving the whole transfer until the REQ line goes down.
+
+This requirement can be fulfilled in two ways:
+
+* By providing a buffer of the size of the maximum packet length.
+* By continuously responding to the RX buffer request event.
+  The latency of the event handling must be taken into account in that case.
+  For example, a flash page erase on some devices might have a significant impact.
+
+See :ref:`bm_lpuarte_sample` sample for the implementation of this driver.

drivers/CMakeLists.txt

@@ -10,3 +10,4 @@ add_compile_options($<TARGET_PROPERTY:compiler,warning_shadow_variables>)
 add_subdirectory_ifdef(CONFIG_CONSOLE console)
 add_subdirectory_ifdef(CONFIG_CLOCK_CONTROL clock_control)
 add_subdirectory_ifdef(CONFIG_FLASH flash)
+add_subdirectory_ifdef(CONFIG_BM_SW_LPUARTE lpuarte)

drivers/Kconfig

@@ -8,6 +8,7 @@ menu "Device Drivers"
 # zephyr-keep-sorted-start
 rsource "console/Kconfig"
 rsource "flash/Kconfig"
+rsource "lpuarte/Kconfig"
 # zephyr-keep-sorted-stop
 
 endmenu

drivers/lpuarte/CMakeLists.txt

@@ -0,0 +1,8 @@
+#
+# Copyright (c) 2025 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+#
+zephyr_library()
+
+zephyr_library_sources(lpuarte.c)

drivers/lpuarte/Kconfig

@@ -0,0 +1,31 @@
+# LPUARTE configuration
+
+# Copyright (c) 2025, Nordic Semiconductor ASA
+# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
+
+config BM_SW_LPUARTE
+	bool "Low Power UARTE using REQ/RDY lines"
+	help
+	  Low Power UARTE implements UARTE API and extends standard UARTE
+	  communication with a 2-pins protocol for receiver wake-up and flow control.
+
+if BM_SW_LPUARTE
+
+# Set number of event handlers used by the LPUART driver
+config NRFX_GPIOTE_NUM_OF_EVT_HANDLERS
+	default 2
+
+config BM_SW_LPUARTE_INT_DRV_TX_BUF_SIZE
+	int "Tx buffer size"
+	default 128
+	depends on BM_SW_LPUARTE_INT_DRIVEN
+	help
+	  Internal buffer of that size is created and used by uart_fifo_fill.
+	  For optimal performance it should be able to fit the longest possible
+	  packet.
+
+module = BM_SW_LPUARTE
+module-str = Low Power UARTE
+source "subsys/logging/Kconfig.template.log_config"
+
+endif