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docs/rc: document RC/LIRC drivers and remove empty drivers/rmt files

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Add documentation for the RC/LIRC character driver subsystem covering
device registration, the LIRC interface, and usage from user space.

Remove placeholder empty files under drivers/rmt that were left over
from the rmtchar era and are no longer referenced.

Signed-off-by: Piyush Patle <piyushpatle228@gmail.com>
This commit is contained in:
Piyush Patle
2026-03-31 18:39:00 +05:30
committed by Alan C. Assis
parent 7b590f9c43
commit 140f2c1c78
11 changed files with 144 additions and 66 deletions
Download Patch File Download Diff File Expand all files Collapse all files
Documentation/components/drivers/character/rc.rst
+136
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@@ -1,3 +1,139 @@
======================
Remote Control Devices
======================
NuttX provides a Remote Control (RC) framework for infrared style input and
output devices. The userspace interface follows the LIRC model and exposes
each device as a character node such as ``/dev/lirc0``.
Like many NuttX drivers, the RC subsystem is split into two parts:
#. a generic upper half in ``drivers/rc/lirc_dev.c``, and
#. a lower half supplied by platform or device specific code.
The upper half handles the character driver registration, per-open buffering,
``poll()`` support, and the common ``ioctl()`` interface. The lower half is
responsible for the hardware specific work such as receiving pulse timings,
transmitting IR data, or reporting decoded scancodes.
Files related to the RC framework are located in:
- ``include/nuttx/lirc.h``
- ``include/nuttx/rc/lirc_dev.h``
- ``drivers/rc/lirc_dev.c``
Application Programming Interface
=================================
Applications should include the following header files:
.. code-block:: c
#include <nuttx/lirc.h>
#include <sys/ioctl.h>
Each RC device is registered as a POSIX character device in ``/dev``.
Applications open the device with the standard ``open()`` call and then use
``read()``, ``write()``, ``poll()``, and ``ioctl()`` just like other character
drivers.
The RC framework supports three kinds of lower-half devices:
- ``LIRC_DRIVER_SCANCODE`` for devices that report decoded scancodes
- ``LIRC_DRIVER_IR_RAW`` for devices that report raw pulse/space timings
- ``LIRC_DRIVER_IR_RAW_TX`` for transmit-only raw devices
Raw Pulse/Space Format
======================
Raw IR timing is transferred in the LIRC ``mode2`` format. Each sample is a
32-bit ``unsigned int`` value. The upper 8 bits describe the sample type and
the lower 24 bits carry the payload, usually a duration in microseconds.
The helpers in ``include/nuttx/lirc.h`` are intended to build and inspect
these values:
- ``LIRC_PULSE(usec)``
- ``LIRC_SPACE(usec)``
- ``LIRC_FREQUENCY(value)``
- ``LIRC_TIMEOUT(usec)``
- ``LIRC_IS_PULSE(sample)``
- ``LIRC_IS_SPACE(sample)``
- ``LIRC_VALUE(sample)``
Typical raw transmit data looks like this:
.. code-block:: c
unsigned int txbuf[] =
{
LIRC_PULSE(9000),
LIRC_SPACE(4500),
LIRC_PULSE(560),
LIRC_SPACE(560),
LIRC_PULSE(560),
};
For raw transmit, ``write()`` expects an odd number of ``unsigned int``
samples. The upper half forwards the pulse/space sequence to the lower-half
``tx_ir()`` callback.
IOCTL Commands
==============
The RC upper half supports the standard LIRC ``ioctl()`` commands defined in
``include/nuttx/lirc.h``. Commonly used commands include:
- ``LIRC_GET_FEATURES``
- ``LIRC_GET_SEND_MODE``
- ``LIRC_GET_REC_MODE``
- ``LIRC_SET_SEND_MODE``
- ``LIRC_SET_REC_MODE``
- ``LIRC_GET_REC_RESOLUTION``
- ``LIRC_SET_SEND_CARRIER``
- ``LIRC_SET_SEND_DUTY_CYCLE``
- ``LIRC_SET_REC_TIMEOUT``
Support for a specific command depends on the lower-half capabilities. In
practice, applications usually start by querying ``LIRC_GET_FEATURES`` and
then only use the operations that the device advertises.
Lower-Half Registration
=======================
Platform code registers an RC lower half by filling ``struct lirc_lowerhalf_s``
and calling ``lirc_register()``.
.. code-block:: c
int ret = lirc_register(lower, devno);
The lower half provides a ``struct lirc_ops_s`` callback table. Depending on
the hardware, it may implement open/close callbacks, raw transmit via
``tx_ir()``, scancode transmit via ``tx_scancode()``, carrier and duty-cycle
configuration, or receive timeout handling.
Testing
-------
The ``irtest`` application in ``nuttx-apps/system/irtest`` can be used to
exercise RC devices from NSH. A typical validation sequence is:
#. open ``/dev/lircN``
#. query ``LIRC_GET_FEATURES``
#. query or set send / receive mode
#. write raw mode2 samples on transmit-capable devices
#. read back mode2 samples from receive-capable devices
Espressif RMT LIRC Adapter
==========================
Espressif targets may provide an arch-local LIRC adapter built on top of the
RMT peripheral:
- ``arch/xtensa/src/common/espressif/esp_lirc.c``
- ``arch/risc-v/src/common/espressif/esp_lirc.c``
These adapters expose the RMT peripheral through the RC framework as
``/dev/lircN`` devices while keeping the hardware specific RMT implementation
in the Espressif lower-half driver.
arch/risc-v/src/common/espressif/Kconfig
-1
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@@ -1288,7 +1288,6 @@ config ESPRESSIF_BROWNOUT_DET
config ESP_RMT
bool "Remote Control Module (RMT)"
default n
select DRIVERS_RC
---help---
The RMT (Remote Control Transceiver) peripheral was designed to act as
an infrared transceiver. However, due to the flexibility of its data
arch/risc-v/src/common/espressif/esp_lirc.h
+8
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@@ -23,10 +23,18 @@
#ifndef __ARCH_RISC_V_SRC_COMMON_ESPRESSIF_ESP_LIRC_H
#define __ARCH_RISC_V_SRC_COMMON_ESPRESSIF_ESP_LIRC_H
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include "esp_rmt.h"
/****************************************************************************
* Public Function Prototypes
****************************************************************************/
#ifndef __ASSEMBLY__
#ifdef __cplusplus
extern "C"
arch/xtensa/src/common/espressif/Kconfig
-1
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@@ -71,7 +71,6 @@ endmenu # Interrupt Configuration
config ESP_RMT
bool "Remote Control Module (RMT)"
default n
select DRIVERS_RC
---help---
The RMT (Remote Control Transceiver) peripheral was designed to act as
an infrared transceiver. However, due to the flexibility of its data
boards/xtensa/esp32/esp32-devkitc/configs/match4/defconfig
-7
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@@ -26,11 +26,7 @@ CONFIG_BUILTIN=y
CONFIG_DEV_GPIO=y
CONFIG_ESP32_UART0=y
CONFIG_ESPRESSIF_GPIO_IRQ=y
CONFIG_ESP_RMT=y
CONFIG_EXAMPLES_GPIO=y
CONFIG_EXAMPLES_RMTCHAR=y
CONFIG_EXAMPLES_RMTCHAR_RX=y
CONFIG_EXAMPLES_RMTCHAR_TX=y
CONFIG_EXAMPLES_WS2812=y
CONFIG_FS_PROCFS=y
CONFIG_GAMES_MATCH4=y
@@ -50,9 +46,6 @@ CONFIG_NSH_READLINE=y
CONFIG_PREALLOC_TIMERS=4
CONFIG_RAM_SIZE=114688
CONFIG_RAM_START=0x20000000
CONFIG_RMT=y
CONFIG_RMTCHAR=y
CONFIG_RMT_DEFAULT_RX_BUFFER_SIZE=256
CONFIG_RR_INTERVAL=200
CONFIG_SCHED_LPWORK=y
CONFIG_SCHED_WAITPID=y
boards/xtensa/esp32/esp32-devkitc/configs/snake/defconfig
-6
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@@ -28,9 +28,6 @@ CONFIG_ESP32_UART0=y
CONFIG_ESPRESSIF_GPIO_IRQ=y
CONFIG_ESP_RMT=y
CONFIG_EXAMPLES_GPIO=y
CONFIG_EXAMPLES_RMTCHAR=y
CONFIG_EXAMPLES_RMTCHAR_RX=y
CONFIG_EXAMPLES_RMTCHAR_TX=y
CONFIG_EXAMPLES_WS2812=y
CONFIG_FS_PROCFS=y
CONFIG_GAMES_SNAKE=y
@@ -50,9 +47,6 @@ CONFIG_NSH_READLINE=y
CONFIG_PREALLOC_TIMERS=4
CONFIG_RAM_SIZE=114688
CONFIG_RAM_START=0x20000000
CONFIG_RMT=y
CONFIG_RMTCHAR=y
CONFIG_RMT_DEFAULT_RX_BUFFER_SIZE=256
CONFIG_RR_INTERVAL=200
CONFIG_SCHED_LPWORK=y
CONFIG_SCHED_WAITPID=y
boards/xtensa/esp32s3/esp32s3-devkit/configs/python/defconfig
-2
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@@ -91,8 +91,6 @@ CONFIG_PSEUDOFS_SOFTLINKS=y
CONFIG_PTHREAD_MUTEX_TYPES=y
CONFIG_RAM_SIZE=114688
CONFIG_RAM_START=0x20000000
CONFIG_RMT=y
CONFIG_RMTCHAR=y
CONFIG_RR_INTERVAL=200
CONFIG_RTC=y
CONFIG_RTC_DRIVER=y
drivers/Makefile
-1
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@@ -59,7 +59,6 @@ include pinctrl/Make.defs
include pipes/Make.defs
include power/Make.defs
include regmap/Make.defs
include rmt/Make.defs
include rpmsg/Make.defs
include rptun/Make.defs
include sensors/Make.defs
drivers/rmt/CMakeLists.txt
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@@ -1,23 +0,0 @@
# ##############################################################################
# drivers/rmt/CMakeLists.txt
#
# SPDX-License-Identifier: Apache-2.0
#
# Licensed to the Apache Software Foundation (ASF) under one or more contributor
# license agreements. See the NOTICE file distributed with this work for
# additional information regarding copyright ownership. The ASF licenses this
# file to you under the Apache License, Version 2.0 (the "License"); you may not
# use this file except in compliance with the License. You may obtain a copy of
# the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under
# the License.
#
# ##############################################################################
# RMT character driver removed; RMT upper-half is now arch/espressif/esp_lirc.c
drivers/rmt/Kconfig
-4
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@@ -1,4 +0,0 @@
#
# For a description of the syntax of this configuration file,
# see the file kconfig-language.txt in the NuttX tools repository.
#
drivers/rmt/Make.defs
-21
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@@ -1,21 +0,0 @@
############################################################################
# drivers/rmt/Make.defs
#
# SPDX-License-Identifier: Apache-2.0
#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership. The
# ASF licenses this file to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance with the
# License. You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
#
############################################################################