Documentation: Add entry about the RMT peripheral for ESP32 family

Add documentation about the RMT peripheral (and using it to drive
WS2812 addressable RGB LEDs) for ESP32-S2, ESP32-S3, ESP32-C3,
ESP32-C6 and ESP32-H2.

Documentation/platforms/risc-v/esp32c3/boards/esp32c3-generic/index.rst

@@ -105,6 +105,35 @@ To test it, just execute the ``pwm`` application::
     pwm_main: starting output with frequency: 10000 duty: 00008000
     pwm_main: stopping output
 
+rmt
+---
+
+This configuration configures the transmitter and the receiver of the
+Remote Control Transceiver (RMT) peripheral on the ESP32-C3 using GPIOs 8
+and 2, respectively. The RMT peripheral is better explained
+`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32c3/api-reference/peripherals/rmt.html>`__,
+in the ESP-IDF documentation. The minimal data unit in the frame is called the
+RMT symbol, which is represented by ``rmt_item32_t`` in the driver:
+
+.. figure:: rmt_symbol.png
+   :align: center
+
+The example ``rmtchar`` can be used to test the RMT peripheral. Connecting
+these pins externally to each other will make the transmitter send RMT items
+and demonstrates the usage of the RMT peripheral::
+
+    nsh> rmtchar
+
+**WS2812 addressable RGB LEDs**
+
+This same configuration enables the usage of the RMT peripheral and the example
+``ws2812`` to drive addressable RGB LEDs::
+
+    nsh> ws2812
+
+Please note that this board contains an on-board WS2812 LED connected to GPIO8
+and, by default, this config configures the RMT transmitter in the same pin.
+
 rtc
 ---
 

Documentation/platforms/risc-v/esp32c6/boards/esp32c6-devkit/index.rst

@@ -140,6 +140,35 @@ To test it, just execute the ``pwm`` application::
     pwm_main: starting output with frequency: 10000 duty: 00008000
     pwm_main: stopping output
 
+rmt
+---
+
+This configuration configures the transmitter and the receiver of the
+Remote Control Transceiver (RMT) peripheral on the ESP32-C6 using GPIOs 8
+and 2, respectively. The RMT peripheral is better explained
+`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32c6/api-reference/peripherals/rmt.html>`__,
+in the ESP-IDF documentation. The minimal data unit in the frame is called the
+RMT symbol, which is represented by ``rmt_item32_t`` in the driver:
+
+.. figure:: rmt_symbol.png
+   :align: center
+
+The example ``rmtchar`` can be used to test the RMT peripheral. Connecting
+these pins externally to each other will make the transmitter send RMT items
+and demonstrates the usage of the RMT peripheral::
+
+    nsh> rmtchar
+
+**WS2812 addressable RGB LEDs**
+
+This same configuration enables the usage of the RMT peripheral and the example
+``ws2812`` to drive addressable RGB LEDs::
+
+    nsh> ws2812
+
+Please note that this board contains an on-board WS2812 LED connected to GPIO8
+and, by default, this config configures the RMT transmitter in the same pin.
+
 rtc
 ---
 

Documentation/platforms/risc-v/esp32h2/boards/esp32h2-devkit/index.rst

@@ -139,6 +139,35 @@ To test it, just execute the ``pwm`` application::
     pwm_main: starting output with frequency: 10000 duty: 00008000
     pwm_main: stopping output
 
+rmt
+---
+
+This configuration configures the transmitter and the receiver of the
+Remote Control Transceiver (RMT) peripheral on the ESP32-H2 using GPIOs 8
+and 2, respectively. The RMT peripheral is better explained
+`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32h2/api-reference/peripherals/rmt.html>`__,
+in the ESP-IDF documentation. The minimal data unit in the frame is called the
+RMT symbol, which is represented by ``rmt_item32_t`` in the driver:
+
+.. figure:: rmt_symbol.png
+   :align: center
+
+The example ``rmtchar`` can be used to test the RMT peripheral. Connecting
+these pins externally to each other will make the transmitter send RMT items
+and demonstrates the usage of the RMT peripheral::
+
+    nsh> rmtchar
+
+**WS2812 addressable RGB LEDs**
+
+This same configuration enables the usage of the RMT peripheral and the example
+``ws2812`` to drive addressable RGB LEDs::
+
+    nsh> ws2812
+
+Please note that this board contains an on-board WS2812 LED connected to GPIO8
+and, by default, this config configures the RMT transmitter in the same pin.
+
 rtc
 ---
 

Documentation/platforms/xtensa/esp32s2/boards/esp32s2-saola-1/index.rst

@@ -335,6 +335,35 @@ To test it, just run ``rand`` to get 32 randomly generated bytes::
     0000  98 b9 66 a2 a2 c0 a2 ae 09 70 93 d1 b5 91 86 c8  ..f......p......
     0010  8f 0e 0b 04 29 64 21 72 01 92 7c a2 27 60 6f 90  ....)d!r..|.'`o.
 
+rmt
+---
+
+This configuration configures the transmitter and the receiver of the
+Remote Control Transceiver (RMT) peripheral on the ESP32-S2 using GPIOs 18
+and 2, respectively. The RMT peripheral is better explained
+`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/api-reference/peripherals/rmt.html>`__,
+in the ESP-IDF documentation. The minimal data unit in the frame is called the
+RMT symbol, which is represented by ``rmt_item32_t`` in the driver:
+
+.. figure:: rmt_symbol.png
+   :align: center
+
+The example ``rmtchar`` can be used to test the RMT peripheral. Connecting
+these pins externally to each other will make the transmitter send RMT items
+and demonstrates the usage of the RMT peripheral::
+
+    nsh> rmtchar
+
+**WS2812 addressable RGB LEDs**
+
+This same configuration enables the usage of the RMT peripheral and the example
+``ws2812`` to drive addressable RGB LEDs::
+
+    nsh> ws2812
+
+Please note that this board contains an on-board WS2812 LED connected to GPIO18
+and, by default, this config configures the RMT transmitter in the same pin.
+
 rtc
 ---
 

Documentation/platforms/xtensa/esp32s3/boards/esp32s3-devkit/index.rst

@@ -46,6 +46,14 @@ Board LEDs
 
 There are several on-board LEDs for that indicate the presence of power
 and USB activity.  None of these are available for use by software.
+Another WS2812 LED is connected to GPIO48 or GPIO38 depending on the boards
+version.
+
+.. note:: Both the initial and v1.1 versions of ESP32-S3-DevKitC-1 are
+   available on the market. The main difference lies in the GPIO assignment
+   for the RGB LED: the initial version (1.0) uses GPIO48, whereas v1.1 uses
+   GPIO38. The initial version is selected by default, but one can select
+   ``CONFIG_ESP32S3_DEVKITC_1_V11`` through ``make menuconfig``.
 
 I2S
 ===
@@ -372,6 +380,37 @@ To test it, just run ``rand`` to get 32 randomly generated bytes::
     0000  98 b9 66 a2 a2 c0 a2 ae 09 70 93 d1 b5 91 86 c8  ..f......p......
     0010  8f 0e 0b 04 29 64 21 72 01 92 7c a2 27 60 6f 90  ....)d!r..|.'`o.
 
+rmt
+---
+
+This configuration configures the transmitter and the receiver of the
+Remote Control Transceiver (RMT) peripheral on the ESP32-S3 using GPIOs 48
+(or 38, depending on the board version) and 2, respectively.
+The RMT peripheral is better explained
+`here <https://docs.espressif.com/projects/esp-idf/en/latest/esp32s3/api-reference/peripherals/rmt.html>`__,
+in the ESP-IDF documentation. The minimal data unit in the frame is called the
+RMT symbol, which is represented by ``rmt_item32_t`` in the driver:
+
+.. figure:: rmt_symbol.png
+   :align: center
+
+The example ``rmtchar`` can be used to test the RMT peripheral. Connecting
+these pins externally to each other will make the transmitter send RMT items
+and demonstrates the usage of the RMT peripheral::
+
+    nsh> rmtchar
+
+**WS2812 addressable RGB LEDs**
+
+This same configuration enables the usage of the RMT peripheral and the example
+``ws2812`` to drive addressable RGB LEDs::
+
+    nsh> ws2812
+
+Please note that this board contains an on-board WS2812 LED connected to GPIO48
+(or GPIO38, depending on the board version) and, by default, this config
+configures the RMT transmitter in the same pin.
+
 rtc
 ---