Introduction
============

This directory contains Device Tree overlays. Device Tree makes it possible
to support many hardware configurations with a single kernel and without the
need to explicitly load or blacklist kernel modules. Note that this isn't a
"pure" Device Tree configuration (c.f. MACH_BCM2835) - some on-board devices
are still configured by the board support code, but the intention is to
eventually reach that goal.

On Raspberry Pi, Device Tree usage is controlled from /boot/config.txt. By
default, the Raspberry Pi kernel boots with device tree enabled. You can
completely disable DT usage (for now) by adding:

    device_tree=

to your config.txt, which should cause your Pi to revert to the old way of
doing things after a reboot.

In /boot you will find a .dtb for each base platform. This describes the
hardware that is part of the Raspberry Pi board. The loader (start.elf and its
siblings) selects the .dtb file appropriate for the platform by name, and reads
it into memory. At this point, all of the optional interfaces (i2c, i2s, spi)
are disabled, but they can be enabled using Device Tree parameters:

    dtparam=i2c=on,i2s=on,spi=on

However, this shouldn't be necessary in many use cases because loading an
overlay that requires one of those interfaces will cause it to be enabled
automatically, and it is advisable to only enable interfaces if they are
needed.

Configuring additional, optional hardware is done using Device Tree overlays
(see below).

raspi-config
============

The Advanced Options section of the raspi-config utility can enable and disable
Device Tree use, as well as toggling the I2C and SPI interfaces. Note that it
is possible to both enable an interface and blacklist the driver, if for some
reason you should want to defer the loading.

Modules
=======

As well as describing the hardware, Device Tree also gives enough information
to allow suitable driver modules to be located and loaded, with the corollary
that unneeded modules are not loaded. As a result it should be possible to
remove lines from /etc/modules, and /etc/modprobe.d/raspi-blacklist.conf can
have its contents deleted (or commented out).

Using Overlays
==============

Overlays are loaded using the "dtoverlay" directive. As an example, consider the
popular lirc-rpi module, the Linux Infrared Remote Control driver. In the
pre-DT world this would be loaded from /etc/modules, with an explicit
"modprobe lirc-rpi" command, or programmatically by lircd. With DT enabled,
this becomes a line in config.txt:

    dtoverlay=lirc-rpi

This causes the file /boot/overlays/lirc-rpi-overlay.dtb to be loaded. By
default it will use GPIOs 17 (out) and 18 (in), but this can be modified using
DT parameters:

    dtoverlay=lirc-rpi,gpio_out_pin=17,gpio_in_pin=13

Parameters always have default values, although in some cases (e.g. "w1-gpio")
it is necessary to provided multiple overlays in order to get the desired
behaviour. See the list of overlays below for a description of the parameters
and their defaults.

The Overlay and Parameter Reference
===================================

N.B. When editing this file, please preserve the indentation levels to make it
simple to parse programmatically. NO HARD TABS.


Name:   <The base DTB>
Info:   Configures the base Raspberry Pi hardware
Load:   <loaded automatically>
Params:
        audio                    Set to "on" to enable the onboard ALSA audio
                                 interface (default "off")

        i2c_arm                  Set to "on" to enable the ARM's i2c interface
                                 (default "off")

        i2c_vc                   Set to "on" to enable the i2c interface
                                 usually reserved for the VideoCore processor
                                 (default "off")

        i2c                      An alias for i2c_arm

        i2c_arm_baudrate         Set the baudrate of the ARM's i2c interface
                                 (default "100000")

        i2c_vc_baudrate          Set the baudrate of the VideoCore i2c interface
                                 (default "100000")

        i2c_baudrate             An alias for i2c_arm_baudrate

        i2s                      Set to "on" to enable the i2s interface
                                 (default "off")

        spi                      Set to "on" to enable the spi interfaces
                                 (default "off")

        random                   Set to "on" to enable the hardware random
                                 number generator (default "on")

        uart0                    Set to "off" to disable uart0 (default "on")

        watchdog                 Set to "on" to enable the hardware watchdog
                                 (default "off")

        act_led_trigger          Choose which activity the LED tracks.
                                 Use "heartbeat" for a nice load indicator.
                                 (default "mmc")

        act_led_activelow        Set to "on" to invert the sense of the LED
                                 (default "off")

        act_led_gpio             Set which GPIO to use for the activity LED
                                 (in case you want to connect it to an external
                                 device)
                                 (default "16" on a non-Plus board, "47" on a
                                 Plus or Pi 2)

        pwr_led_trigger
        pwr_led_activelow
        pwr_led_gpio
                                 As for act_led_*, but using the PWR LED.
                                 Not available on Model A/B boards.

        N.B. It is recommended to only enable those interfaces that are needed.
        Leaving all interfaces enabled can lead to unwanted behaviour (i2c_vc
        interfering with Pi Camera, I2S and SPI hogging GPIO pins, etc.)
        Note also that i2c, i2c_arm and i2c_vc are aliases for the physical
        interfaces i2c0 and i2c1. Use of the numeric variants is still possible
        but deprecated because the ARM/VC assignments differ between board
        revisions. The same board-specific mapping applies to i2c_baudrate,
        and the other i2c baudrate parameters.


Name:   ads7846
Info:   ADS7846 Touch controller
Load:   dtoverlay=ads7846,<param>=<val>
Params: cs                       SPI bus Chip Select (default 1)
        speed                    SPI bus speed (default 2MHz, max 3.25MHz)
        penirq                   GPIO used for PENIRQ. REQUIRED
        penirq_pull              Set GPIO pull (default 0=none, 2=pullup)
        swapxy                   Swap x and y axis
        xmin                     Minimum value on the X axis (default 0)
        ymin                     Minimum value on the Y axis (default 0)
        xmax                     Maximum value on the X axis (default 4095)
        ymax                     Maximum value on the Y axis (default 4095)
        pmin                     Minimum reported pressure value (default 0)
        pmax                     Maximum reported pressure value (default 65535)
        xohms                    Touchpanel sensitivity (X-plate resistance)
                                 (default 400)

        penirq is required and usually xohms (60-100) has to be set as well.
        Apart from that, pmax (255) and swapxy are also common.
        The rest of the calibration can be done with xinput-calibrator.
        See: github.com/notro/fbtft/wiki/FBTFT-on-Raspian
        Device Tree binding document:
        www.kernel.org/doc/Documentation/devicetree/bindings/input/ads7846.txt


Name:   at86rf233
Info:   Configures the Atmel AT86RF233 802.15.4 low-power WPAN transceiver,
        connected to spi0.0
Load:   dtoverlay=at86rf233,<param>=<val>
Params: interrupt                GPIO used for INT (default 23)
        reset                    GPIO used for Reset (default 24)
        sleep                    GPIO used for Sleep (default 25)
        speed                    SPI bus speed in Hz (default 6000000)
        trim                     Fine tuning of the internal capacitance
                                 arrays (0=+0pF, 15=+4.5pF, default 15)


Name:   bmp085_i2c-sensor
Info:   Configures the BMP085/BMP180 digital barometric pressure and temperature
        sensors from Bosch Sensortec
Load:   dtoverlay=bmp085_i2c-sensor
Params: <None>


Name:   dht11
Info:   Overlay for the DHT11/DHT21/DHT22 humidity/temperature sensors
        Also sometimes found with the part number(s) AM230x.
Load:   dtoverlay=dht11,<param>=<val>
Params: gpiopin                  GPIO connected to the sensor's DATA output.
                                 (default 4)


[ The ds1307-rtc overlay has been deleted. See i2c-rtc. ]


Name:   enc28j60
Info:   Overlay for the Microchip ENC28J60 Ethernet Controller (SPI)
Load:   dtoverlay=enc28j60,<param>=<val>
Params: int_pin                  GPIO used for INT (default 25)

        speed                    SPI bus speed (default 12000000)


Name:   gpio-ir
Info:   Use GPIO pin as rc-core style infrared receiver input. The rc-core-
        based gpio_ir_recv driver maps received keys directly to a
        /dev/input/event* device, all decoding is done by the kernel - LIRC is
        not required! The key mapping and other decoding parameters can be
        configured by "ir-keytable" tool.
Load:   dtoverlay=gpio-ir,<param>=<val>
Params: gpio_pin                 Input pin number. Default is 18.

        gpio_pull                Desired pull-up/down state (off, down, up)
                                 Default is "down".

        rc-map-name              Default rc keymap (can also be changed by
                                 ir-keytable), defaults to "rc-rc6-mce"


Name:   gpio-poweroff
Info:   Drives a GPIO high or low on reboot
Load:   dtoverlay=gpio-poweroff,<param>=<val>
Params: gpiopin                  GPIO for signalling (default 26)

        active_low               Set if the power control device requires a
                                 high->low transition to trigger a power-down.
                                 Note that this will require the support of a
                                 custom dt-blob.bin to prevent a power-down
                                 during the boot process, and that a reboot
                                 will also cause the pin to go low.


Name:   hifiberry-amp
Info:   Configures the HifiBerry Amp and Amp+ audio cards
Load:   dtoverlay=hifiberry-amp
Params: <None>


Name:   hifiberry-dac
Info:   Configures the HifiBerry DAC audio card
Load:   dtoverlay=hifiberry-dac
Params: <None>


Name:   hifiberry-dacplus
Info:   Configures the HifiBerry DAC+ audio card
Load:   dtoverlay=hifiberry-dacplus
Params: <None>


Name:   hifiberry-digi
Info:   Configures the HifiBerry Digi audio card
Load:   dtoverlay=hifiberry-digi
Params: <None>


Name:   hy28a
Info:   HY28A - 2.8" TFT LCD Display Module by HAOYU Electronics
        Default values match Texy's display shield
Load:   dtoverlay=hy28a,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        xohms                    Touchpanel sensitivity (X-plate resistance)

        resetgpio                GPIO used to reset controller

        ledgpio                  GPIO used to control backlight


Name:   hy28b
Info:   HY28B - 2.8" TFT LCD Display Module by HAOYU Electronics
        Default values match Texy's display shield
Load:   dtoverlay=hy28b,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        xohms                    Touchpanel sensitivity (X-plate resistance)

        resetgpio                GPIO used to reset controller

        ledgpio                  GPIO used to control backlight


Name:   i2c-gpio
Info:   Adds support for software i2c controller on gpio pins
Load:   dtoverlay=i2c-gpio,<param>=<val>
Params: i2c_gpio_sda             GPIO used for I2C data (default "23")

        i2c_gpio_scl             GPIO used for I2C clock (default "24")

        i2c_gpio_delay_us        Clock delay in microseconds
                                 (default "2" = ~100kHz)


Name:   i2c-rtc
Info:   Adds support for a number of I2C Real Time Clock devices
Load:   dtoverlay=i2c-rtc,<param>=<val>
Params: ds1307                   Select the DS1307 device

        ds3231                   Select the DS3231 device

        mcp7941x                 Select the MCP7941x device

        pcf2127                  Select the PCF2127 device

        pcf8523                  Select the PCF8523 device

        pcf8563                  Select the PCF8563 device


Name:   i2s-mmap
Info:   Enables mmap support in the bcm2708-i2s driver
Load:   dtoverlay=i2s-mmap
Params: <None>


Name:   iqaudio-dac
Info:   Configures the IQaudio DAC audio card
Load:   dtoverlay=iqaudio-dac
Params: <None>


Name:   iqaudio-dacplus
Info:   Configures the IQaudio DAC+ audio card
Load:   dtoverlay=iqaudio-dacplus
Params: <None>


Name:   lirc-rpi
Info:   Configures lirc-rpi (Linux Infrared Remote Control for Raspberry Pi)
        Consult the module documentation for more details.
Load:   dtoverlay=lirc-rpi,<param>=<val>
Params: gpio_out_pin             GPIO for output (default "17")

        gpio_in_pin              GPIO for input (default "18")

        gpio_in_pull             Pull up/down/off on the input pin
                                 (default "down")

        sense                    Override the IR receive auto-detection logic:
                                   "0" = force active-high
                                   "1" = force active-low
                                   "-1" = use auto-detection
                                 (default "-1")

        softcarrier              Turn the software carrier "on" or "off"
                                 (default "on")

        invert                   "on" = invert the output pin (default "off")

        debug                    "on" = enable additional debug messages
                                 (default "off")


Name:   mcp2515-can0
Info:   Configures the MCP2515 CAN controller on spi0.0
Load:   dtoverlay=mcp2515-can0,<param>=<val>
Params: oscillator               Clock frequency for the CAN controller (Hz)

        spimaxfrequency          Maximum SPI frequence (Hz)

        interrupt                GPIO for interrupt signal


Name:   mcp2515-can1
Info:   Configures the MCP2515 CAN controller on spi0.1
Load:   dtoverlay=mcp2515-can1,<param>=<val>
Params: oscillator               Clock frequency for the CAN controller (Hz)

        spimaxfrequency          Maximum SPI frequence (Hz)

        interrupt                GPIO for interrupt signal


Name:   mmc
Info:   Selects the bcm2835-mmc SD/MMC driver, optionally with overclock
Load:   dtoverlay=mmc,<param>=<val>
Params: overclock_50             Clock (in MHz) to use when the MMC framework
                                 requests 50MHz
        force_pio                Disable DMA support


Name:   mz61581
Info:   MZ61581 display by Tontec
Load:   dtoverlay=mz61581,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        txbuflen                 Transmit buffer length (default 32768)

        debug                    Debug output level {0-7}

        xohms                    Touchpanel sensitivity (X-plate resistance)


[ The pcf2127-rtc overlay has been deleted. See i2c-rtc. ]


[ The pcf8523-rtc overlay has been deleted. See i2c-rtc. ]


[ The pcf8563-rtc overlay has been deleted. See i2c-rtc. ]


Name:   piscreen
Info:   PiScreen display by OzzMaker.com
Load:   dtoverlay=piscreen,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        xohms                    Touchpanel sensitivity (X-plate resistance)


Name:   piscreen2r
Info:   PiScreen 2 with resistive TP display by OzzMaker.com
Load:   dtoverlay=piscreen2r,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        xohms                    Touchpanel sensitivity (X-plate resistance)


Name:   pitft28-capacitive
Info:   Adafruit PiTFT 2.8" capacitive touch screen
Load:   dtoverlay=pitft28-capacitive,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        touch-sizex              Touchscreen size x (default 240)

        touch-sizey              Touchscreen size y (default 320)

        touch-invx               Touchscreen inverted x axis

        touch-invy               Touchscreen inverted y axis

        touch-swapxy             Touchscreen swapped x y axis


Name:   pitft28-resistive
Info:   Adafruit PiTFT 2.8" resistive touch screen
Load:   dtoverlay=pitft28-resistive,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}


Name:   pps-gpio
Info:   Configures the pps-gpio (pulse-per-second time signal via GPIO).
Load:   dtoverlay=pps-gpio,<param>=<val>
Params: gpiopin                  Input GPIO (default "18")


Name:   pwm
Info:   Configures a single PWM channel
        Legal pin,function combinations for each channel:
          PWM0: 12,4(Alt0) 18,2(Alt5) 40,4(Alt0)            52,5(Alt1)
          PWM1: 13,4(Alt0) 19,2(Alt5) 41,4(Alt0) 45,4(Alt0) 53,5(Alt1)
        N.B.:
          1) Pin 18 is the only one available on all platforms, and
             it is the one used by the I2S audio interface.
             Pins 12 and 13 might be better choices on an A+, B+ or Pi2.
          2) The onboard analogue audio output uses both PWM channels.
          3) So be careful mixing audio and PWM.
          4) Currently the clock must have been enabled and configured
             by other means.
Load:   dtoverlay=pwm,<param>=<val>
Params: pin                      Output pin (default 18) - see table
        func                     Pin function (default 2 = Alt5) - see above
        clock                    PWM clock frequency (informational)


Name:   pwm-2chan
Info:   Configures both PWM channels
        Legal pin,function combinations for each channel:
          PWM0: 12,4(Alt0) 18,2(Alt5) 40,4(Alt0)            52,5(Alt1)
          PWM1: 13,4(Alt0) 19,2(Alt5) 41,4(Alt0) 45,4(Alt0) 53,5(Alt1)
        N.B.:
          1) Pin 18 is the only one available on all platforms, and
             it is the one used by the I2S audio interface.
             Pins 12 and 13 might be better choices on an A+, B+ or Pi2.
          2) The onboard analogue audio output uses both PWM channels.
          3) So be careful mixing audio and PWM.
          4) Currently the clock must have been enabled and configured
             by other means.
Load:   dtoverlay=pwm-2chan,<param>=<val>
Params: pin                      Output pin (default 18) - see table
        pin2                     Output pin for other channel (default 19)
        func                     Pin function (default 2 = Alt5) - see above
        func2                    Function for pin2 (default 2 = Alt5)
        clock                    PWM clock frequency (informational)


Name:   raspidac3
Info:   Configures the RaspiDAV Rev.3x audio card
Load:   dtoverlay=raspidac3
Params: <None>


Name:   rpi-backlight
Info:   Raspberry Pi official display backlight driver
Load:   dtoverlay=rpi-backlight
Params: <None>


Name:   rpi-dac
Info:   Configures the RPi DAC audio card
Load:   dtoverlay=rpi-dac
Params: <None>


Name:   rpi-display
Info:   RPi-Display - 2.8" Touch Display by Watterott
Load:   dtoverlay=rpi-display,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        xohms                    Touchpanel sensitivity (X-plate resistance)


Name:   rpi-ft5406
Info:   Official Raspberry Pi display touchscreen
Load:   dtoverlay=rpi-ft5406
Params: <None>


Name:   rpi-proto
Info:   Configures the RPi Proto audio card
Load:   dtoverlay=rpi-proto
Params: <None>


Name:   rpi-sense
Info:   Raspberry Pi Sense HAT
Load:   dtoverlay=rpi-sense
Params: <None>


Name:   sdhost
Info:   Selects the bcm2835-sdhost SD/MMC driver, optionally with overclock
Load:   dtoverlay=sdhost,<param>=<val>
Params: overclock_50             Clock (in MHz) to use when the MMC framework
                                 requests 50MHz

        force_pio                Disable DMA support (default off)

        pio_limit                Number of blocks above which to use DMA
                                 (default 1)

        debug                    Enable debug output (default off)


Name:   sdio
Info:   Selects the bcm2835-sdhost SD/MMC driver, optionally with overclock,
        and enables SDIO via GPIOs 22-27.
Load:   dtoverlay=sdio,<param>=<val>
Params: overclock_50             Clock (in MHz) to use when the MMC framework
                                 requests 50MHz

        force_pio                Disable DMA support (default off)

        pio_limit                Number of blocks above which to use DMA
                                 (default 1)

        debug                    Enable debug output (default off)

        poll_once                Disable SDIO-device polling every second
                                 (default on: polling once at boot-time)

        bus_width                Set the SDIO host bus width (default 4 bits)


Name:   smi
Info:   Enables the Secondary Memory Interface peripheral. Uses GPIOs 2-25!
Load:   dtoverlay=smi
Params: <None>


Name:   smi-dev
Info:   Enables the userspace interface for the SMI driver
Load:   dtoverlay=smi-dev
Params: <None>


Name:   smi-nand
Info:   Enables access to NAND flash via the SMI interface
Load:   dtoverlay=smi-nand
Params: <None>


Name:   spi-bcm2708
Info:   Selects the bcm2708-spi SPI driver
Load:   dtoverlay=spi-bcm2708
Params: <None>


Name:   spi-bcm2835
Info:   Selects the bcm2835-spi SPI driver
Load:   dtoverlay=spi-bcm2835
Params: <None>


Name:   spi-dma
Info:   enables dma modes for spi-bcm2835
Load:   dtoverlay=spi-dma
Params: <None>


Name:   tinylcd35
Info:   3.5" Color TFT Display by www.tinylcd.com
        Options: Touch, RTC, keypad
Load:   dtoverlay=tinylcd35,<param>=<val>
Params: speed                    Display SPI bus speed

        rotate                   Display rotation {0,90,180,270}

        fps                      Delay between frame updates

        debug                    Debug output level {0-7}

        touch                    Enable touch panel

        touchgpio                Touch controller IRQ GPIO

        xohms                    Touchpanel: Resistance of X-plate in ohms

        rtc-pcf                  PCF8563 Real Time Clock

        rtc-ds                   DS1307 Real Time Clock

        keypad                   Enable keypad

        Examples:
            Display with touchpanel, PCF8563 RTC and keypad:
                dtoverlay=tinylcd35,touch,rtc-pcf,keypad
            Old touch display:
                dtoverlay=tinylcd35,touch,touchgpio=3


Name:   uart1
Info:   Enable uart1 in place of uart0
Load:   dtoverlay=uart1,<param>=<val>
Params: txd1_pin                 GPIO pin for TXD1 (14, 32 or 40 - default 14)

        rxd1_pin                 GPIO pin for RXD1 (15, 33 or 41 - default 15)


Name:   vc4-kms-v3d
Info:   Enable Eric Anholt's DRM VC4 HDMI/HVS/V3D driver. Running startx or
        booting to GUI while this overlay is in use will cause interesting
        lockups.
Load:   dtoverlay=vc4-kms-v3d
Params: <None>


Name:   vga666
Info:   Overlay for the Fen Logic VGA666 board
        This uses GPIOs 2-21 (so no I2C), and activates the output 2-3 seconds
        after the kernel has started.
Load:   dtoverlay=vga666
Params: <None>


Name:   w1-gpio
Info:   Configures the w1-gpio Onewire interface module.
        Use this overlay if you *don't* need a GPIO to drive an external pullup.
Load:   dtoverlay=w1-gpio,<param>=<val>
Params: gpiopin                  GPIO for I/O (default "4")

        pullup                   Non-zero, "on", or "y" to enable the parasitic
                                 power (2-wire, power-on-data) feature


Name:   w1-gpio-pullup
Info:   Configures the w1-gpio Onewire interface module.
        Use this overlay if you *do* need a GPIO to drive an external pullup.
Load:   dtoverlay=w1-gpio-pullup,<param>=<val>
Params: gpiopin                  GPIO for I/O (default "4")

        pullup                   Non-zero, "on", or "y" to enable the parasitic
                                 power (2-wire, power-on-data) feature

        extpullup                GPIO for external pullup (default "5")


Troubleshooting
===============

If you are experiencing problems that you think are DT-related, enable DT
diagnostic output by adding this to /boot/config.txt:

    dtdebug=on

and rebooting. Then run:

    sudo vcdbg log msg

and look for relevant messages.

Further reading
===============

This is only meant to be a quick introduction to the subject of Device Tree on
Raspberry Pi. There is a more complete explanation here:

http://www.raspberrypi.org/documentation/configuration/device-tree.md
