Device Drivers

NuttX supports a variety of device drivers, which can be broadly divided in three classes:

Note

Device driver support depends on the in-memory, pseudo file system that is enabled by default.

Lower-half and upper-half

Drivers in NuttX generally work in two distinct layers:

  • An upper half which registers itself to NuttX using a call such as register_driver() or register_blockdriver() and implements the corresponding high-level interface (read, write, close, etc.). implements the interface. This upper half calls into the lower half via callbacks.

  • A “lower half” which is typically hardware-specific. This is usually implemented at the architecture or board level.

Subdirectories of nuttx/drivers

  • 1wire/ One Wire Drivers

    1wire device drivers.

  • analog/ Analog (ADC/DAC) Drivers

    This directory holds implementations of analog device drivers. This includes drivers for Analog to Digital Conversion (ADC) as well as drivers for Digital to Analog Conversion (DAC).

  • audio/ Audio Device Drivers

    Audio device drivers.

  • bch/ Block Driver to Character Driver

    Contains logic that may be used to convert a block driver into a character driver. This is the complementary conversion as that performed by loop.c.

  • can/ CAN Drivers

    This is the CAN drivers and logic support.

  • clk/Clock management (CLK)

    Clock management (CLK) device drivers.

  • contactless/ Constactless Devices

    Contactless devices are related to wireless devices. They are not communication devices with other similar peers, but couplers/interfaces to contactless cards and tags.

  • crypto/ Crypto Drivers

    Contains crypto drivers and support logic, including the /dev/urandom device.

  • devicetree/ Device Tree support

    Device Tree support.

  • dma/ DMA Drivers

    DMA drivers support.

  • eeprom/ EEPROM

    An EEPROM is a form of Memory Technology Device (see drivers/mtd). EEPROMs are non-volatile memory like FLASH, but differ in underlying memory technology and differ in usage in many respects: They may not be organized into blocks (at least from the standpoint of the user) and it is not necessary to erase the EEPROM memory before re-writing it. In addition, EEPROMs tend to be much smaller than FLASH parts, usually only a few kilobytes vs megabytes for FLASH. EEPROM tends to be used to retain a small amount of device configuration information; FLASH tends to be used for program or massive data storage. For these reasons, it may not be convenient to use the more complex MTD interface but instead use the simple character interface provided by the EEPROM drivers.

  • efuse/ EFUSE Drivers

    EFUSE drivers support.

  • i2c/ I2C Device Drivers

    I2C drivers and support logic.

  • i2s/ I2S Drivers

    I2S drivers and support logic.

  • input/ Input Devices

    This directory holds implementations of human input device (HID) drivers. This includes such things as mouse, touchscreen, joystick, keyboard and keypad drivers.

    Note that USB HID devices are treated differently. These can be found under usbdev/ or usbhost/.

  • ioexpander/ IO Expander Device Drivers

    IO Expander drivers.

  • ipcc/ IPCC (Inter Processor Communication Controller) Driver

    IPCC (Inter Processor Communication Controller) driver.

  • lcd/ LCD Character Drivers

    Drivers for parallel and serial LCD and OLED type devices.

  • leds/ LEDS

    Various LED-related drivers including discrete as well as PWM- driven LEDs.

  • loop/ Loop Device

    Supports the standard loop device that can be used to export a file (or character device) as a block device.

    See losetup() and loteardown() in include/nuttx/fs/fs.h.

  • math/ Math Acceleration Drivers

    MATH Acceleration drivers.

  • misc/ dev_null.c and dev_zero.c rwbuffer.c ramdisk.c

    Various drivers that don’t fit elsewhere.

  • mmcsd/ SDIO Device Drivers MMCSD Device Drivers

    Support for MMC/SD block drivers. MMC/SD block drivers based on SPI and SDIO/MCI interfaces are supported.

  • modem/ Modem Device

    Modem Support.

  • motor/ Motor Drivers

    Motor control drivers.

  • mtd/ Memory Technology Device Drivers

    Memory Technology Device (MTD) drivers. Some simple drivers for memory technologies like FLASH, EEPROM, NVRAM, etc.

    (Note: This is a simple memory interface and should not be confused with the “real” MTD developed at infradead.org. This logic is unrelated; I just used the name MTD because I am not aware of any other common way to refer to this class of devices).

  • net/ Network interface drivers

    Network interface drivers.

  • notes/ Note Driver Interface

    Note Driver Support.

  • pipes/ FIFO and named pipe drivers

    FIFO and named pipe drivers. Standard interfaces are declared in include/unistd.h

  • power/ Power-related Drivers

    Various drivers related to power management.

  • rc/ Remote Control Devices

    Remote Control Device Support.

  • regmap/ drivers/regmap

    Regmap Subsystems Support.

  • reset/ Reset Driver

    Reset Driver Support.

  • rf/ RF Devices

    RF Device Support.

  • rptun/ Remote Proc Tunnel Drivers

    Remote Proc Tunnel Driver Support.

  • segger/ Segger RTT drivers

    Segger RTT drivers.

  • sensors/ Sensor Drivers

    Drivers for various sensors. A sensor driver differs little from other types of drivers other than they are use to provide measurements of things in environment like temperature, orientation, acceleration, altitude, direction, position, etc.

    DACs might fit this definition of a sensor driver as well since they measure and convert voltage levels. DACs, however, are retained in the analog/ sub-directory.

  • serial/Serial Device Drivers

    Front-end character drivers for chip-specific UARTs. This provide some TTY-like functionality and are commonly used (but not required for) the NuttX system console.

  • spi/ SPI Device Drivers

    SPI drivers and support logic.

  • syslog/ SYSLOG

    System logging devices.

  • timers/ Timers Drivers

    Includes support for various timer devices.

  • usbdev/ USB Device-Side Drivers

    USB device drivers.

  • usbhost/ USB Host-Side Drivers

    USB host drivers.

  • usbmisc/ USB Miscellaneous Drivers

    USB Miscellaneous drivers.

  • usbmonitor/ USB Monitor support

    USB Monitor support.

  • usrsock/ Usrsock Driver

    Usrsock Driver Support.

  • video/ Video Device Drivers

    Video-related drivers.

  • virtio/ Virtio Device Drivers

    Virtio Device Support.

  • wireless/ Wireless Drivers

    Drivers for various wireless devices.

Skeleton Files

Skeleton files are “empty” frameworks for NuttX drivers. They are provided to give you a good starting point if you want to create a new NuttX driver. The following skeleton files are available:

  • drivers/lcd/skeleton.c Skeleton LCD driver

  • drivers/mtd/skeleton.c Skeleton memory technology device drivers

  • drivers/net/skeleton.c Skeleton network/Ethernet drivers

  • drivers/usbhost/usbhost_skeleton.c Skeleton USB host class driver