README

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).

GPIO numbering uses the hardware pin numbering scheme (aka BCM scheme) and
not the physical pin numbers.

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" config.txt setting. As an example,
consider I2C Real Time Clock drivers. In the pre-DT world these would be loaded
by writing a magic string comprising a device identifier and an I2C address to
a special file in /sys/class/i2c-adapter, having first loaded the driver for
the I2C interface and the RTC device - something like this:

    modprobe i2c-bcm2835
    modprobe rtc-ds1307
    echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device

With DT enabled, this becomes a line in config.txt:

    dtoverlay=i2c-rtc,ds1307

This causes the file /boot/overlays/i2c-rtc.dtbo to be loaded and a "node"
describing the DS1307 I2C device to be added to the Device Tree for the Pi. By
default it usees address 0x68, but this can be modified with an additional DT
parameter:

    dtoverlay=i2c-rtc,ds1307,addr=0x68

Parameters usually have default values, although certain parameters are
mandatory. 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:
        ant1                    Select antenna 1 (default). CM4 only.

        ant2                    Select antenna 2. CM4 only.

        noant                   Disable both antennas. CM4 only.

        audio                   Set to "on" to enable the onboard ALSA audio
                                interface (default "off")

        axiperf                 Set to "on" to enable the AXI bus performance
                                monitors.
                                See /sys/kernel/debug/raspberrypi_axi_monitor
                                for the results.

        eee                     Enable Energy Efficient Ethernet support for
                                compatible devices (default "on"). See also
                                "tx_lpi_timer". Pi3B+ only.

        eth_downshift_after     Set the number of auto-negotiation failures
                                after which the 1000Mbps modes are disabled.
                                Legal values are 2, 3, 4, 5 and 0, where
                                0 means never downshift (default 2). Pi3B+ only.

        eth_led0                Set mode of LED0 - amber on Pi3B+ (default "1"),
                                green on Pi4 (default "0").
                                The legal values are:

                                Pi3B+

                                0=link/activity          1=link1000/activity
                                2=link100/activity       3=link10/activity
                                4=link100/1000/activity  5=link10/1000/activity
                                6=link10/100/activity    14=off    15=on

                                Pi4

                                0=Speed/Activity         1=Speed
                                2=Flash activity         3=FDX
                                4=Off                    5=On
                                6=Alt                    7=Speed/Flash
                                8=Link                   9=Activity

        eth_led1                Set mode of LED1 - green on Pi3B+ (default "6"),
                                amber on Pi4 (default "8"). See eth_led0 for
                                legal values.

        eth_max_speed           Set the maximum speed a link is allowed
                                to negotiate. Legal values are 10, 100 and
                                1000 (default 1000). Pi3B+ only.

        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")

        krnbt                   Set to "on" to enable autoprobing of Bluetooth
                                driver without need of hciattach/btattach
                                (default "off")

        krnbt_baudrate          Set the baudrate of the PL011 UART when used
                                with krnbt=on

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

        spi_dma4                Use to enable 40-bit DMA on spi interfaces
                                (the assigned value doesn't matter)
                                (2711 only)

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

        sd_overclock            Clock (in MHz) to use when the MMC framework
                                requests 50MHz

        sd_poll_once            Looks for a card once after booting. Useful
                                for network booting scenarios to avoid the
                                overhead of continuous polling. N.B. Using
                                this option restricts the system to using a
                                single card per boot (or none at all).
                                (default off)

        sd_force_pio            Disable DMA support for SD driver (default off)

        sd_pio_limit            Number of blocks above which to use DMA for
                                SD card (default 1)

        sd_debug                Enable debug output from SD driver (default off)

        sdio_overclock          Clock (in MHz) to use when the MMC framework
                                requests 50MHz for the SDIO/WiFi interface.

        tx_lpi_timer            Set the delay in microseconds between going idle
                                and entering the low power state (default 600).
                                Requires EEE to be enabled - see "eee".

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

        uart1                   Set to "on" or "off" to enable or disable uart1
                                (default varies)

        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")
                                N.B. For Pi 3B, 3B+, 3A+ and 4B, use the act-led
                                overlay.

        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)
                                N.B. For Pi 3B, 3B+, 3A+ and 4B, use the act-led
                                overlay.

        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:   act-led
Info:   Pi 3B, 3B+, 3A+ and 4B use a GPIO expander to drive the LEDs which can
        only be accessed from the VPU. There is a special driver for this with a
        separate DT node, which has the unfortunate consequence of breaking the
        act_led_gpio and act_led_activelow dtparams.
        This overlay changes the GPIO controller back to the standard one and
        restores the dtparams.
Load:   dtoverlay=act-led,<param>=<val>
Params: activelow               Set to "on" to invert the sense of the LED
                                (default "off")

        gpio                    Set which GPIO to use for the activity LED
                                (in case you want to connect it to an external
                                device)
                                REQUIRED


Name:   adafruit18
Info:   Overlay for the SPI-connected Adafruit 1.8" display (based on the
        ST7735R chip). It includes support for the "green tab" version.
Load:   dtoverlay=adafruit18,<param>=<val>
Params: green                   Use the adafruit18_green variant.
        rotate                  Display rotation {0,90,180,270}
        speed                   SPI bus speed in Hz (default 4000000)
        fps                     Display frame rate in Hz
        bgr                     Enable BGR mode (default off)
        debug                   Debug output level {0-7}
        dc_pin                  GPIO pin for D/C (default 24)
        reset_pin               GPIO pin for RESET (default 25)
        led_pin                 GPIO used to control backlight (default 18)


Name:   adau1977-adc
Info:   Overlay for activation of ADAU1977 ADC codec over I2C for control
        and I2S for data.
Load:   dtoverlay=adau1977-adc
Params: <None>


Name:   adau7002-simple
Info:   Overlay for the activation of ADAU7002 stereo PDM to I2S converter.
Load:   dtoverlay=adau7002-simple,<param>=<val>
Params: card-name               Override the default, "adau7002", card name.


Name:   ads1015
Info:   Overlay for activation of Texas Instruments ADS1015 ADC over I2C
Load:   dtoverlay=ads1015,<param>=<val>
Params: addr                    I2C bus address of device. Set based on how the
                                addr pin is wired. (default=0x48 assumes addr
                                is pulled to GND)
        cha_enable              Enable virtual channel a. (default=true)
        cha_cfg                 Set the configuration for virtual channel a.
                                (default=4 configures this channel for the
                                voltage at A0 with respect to GND)
        cha_datarate            Set the datarate (samples/sec) for this channel.
                                (default=4 sets 1600 sps)
        cha_gain                Set the gain of the Programmable Gain
                                Amplifier for this channel. (default=2 sets the
                                full scale of the channel to 2.048 Volts)

        Channel (ch) parameters can be set for each enabled channel.
        A maximum of 4 channels can be enabled (letters a thru d).
        For more information refer to the device datasheet at:
        http://www.ti.com/lit/ds/symlink/ads1015.pdf


Name:   ads1115
Info:   Texas Instruments ADS1115 ADC
Load:   dtoverlay=ads1115,<param>[=<val>]
Params: addr                    I2C bus address of device. Set based on how the
                                addr pin is wired. (default=0x48 assumes addr
                                is pulled to GND)
        cha_enable              Enable virtual channel a.
        cha_cfg                 Set the configuration for virtual channel a.
                                (default=4 configures this channel for the
                                voltage at A0 with respect to GND)
        cha_datarate            Set the datarate (samples/sec) for this channel.
                                (default=7 sets 860 sps)
        cha_gain                Set the gain of the Programmable Gain
                                Amplifier for this channel. (Default 1 sets the
                                full scale of the channel to 4.096 Volts)

        Channel parameters can be set for each enabled channel.
        A maximum of 4 channels can be enabled (letters a thru d).
        For more information refer to the device datasheet at:
        http://www.ti.com/lit/ds/symlink/ads1115.pdf


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:   adv7282m
Info:   Analog Devices ADV7282M analogue video to CSI2 bridge.
        Uses Unicam1, which is the standard camera connector on most Pi
        variants.
Load:   dtoverlay=adv7282m,<param>=<val>
Params: addr                    Overrides the I2C address (default 0x21)


Name:   adv728x-m
Info:   Analog Devices ADV728[0|1|2]-M analogue video to CSI2 bridges.
        This is a wrapper for adv7282m, and defaults to ADV7282M.
Load:   dtoverlay=adv728x-m,<param>=<val>
Params: addr                    Overrides the I2C address (default 0x21)
        adv7280m                Select ADV7280-M.
        adv7281m                Select ADV7281-M.
        adv7281ma               Select ADV7281-MA.


Name:   akkordion-iqdacplus
Info:   Configures the Digital Dreamtime Akkordion Music Player (based on the
        OEM IQAudIO DAC+ or DAC Zero module).
Load:   dtoverlay=akkordion-iqdacplus,<param>=<val>
Params: 24db_digital_gain       Allow gain to be applied via the PCM512x codec
                                Digital volume control. Enable with
                                dtoverlay=akkordion-iqdacplus,24db_digital_gain
                                (The default behaviour is that the Digital
                                volume control is limited to a maximum of
                                0dB. ie. it can attenuate but not provide
                                gain. For most users, this will be desired
                                as it will prevent clipping. By appending
                                the 24db_digital_gain parameter, the Digital
                                volume control will allow up to 24dB of
                                gain. If this parameter is enabled, it is the
                                responsibility of the user to ensure that
                                the Digital volume control is set to a value
                                that does not result in clipping/distortion!)


Name:   allo-boss-dac-pcm512x-audio
Info:   Configures the Allo Boss DAC audio cards.
Load:   dtoverlay=allo-boss-dac-pcm512x-audio,<param>
Params: 24db_digital_gain       Allow gain to be applied via the PCM512x codec
                                Digital volume control. Enable with
                                "dtoverlay=allo-boss-dac-pcm512x-audio,
                                24db_digital_gain"
                                (The default behaviour is that the Digital
                                volume control is limited to a maximum of
                                0dB. ie. it can attenuate but not provide
                                gain. For most users, this will be desired
                                as it will prevent clipping. By appending
                                the 24db_digital_gain parameter, the Digital
                                volume control will allow up to 24dB of
                                gain. If this parameter is enabled, it is the
                                responsibility of the user to ensure that
                                the Digital volume control is set to a value
                                that does not result in clipping/distortion!)
        slave                   Force Boss DAC into slave mode, using Pi a
                                master for bit clock and frame clock. Enable
                                with "dtoverlay=allo-boss-dac-pcm512x-audio,
                                slave"


Name:   allo-digione
Info:   Configures the Allo Digione audio card
Load:   dtoverlay=allo-digione
Params: <None>


Name:   allo-katana-dac-audio
Info:   Configures the Allo Katana DAC audio card
Load:   dtoverlay=allo-katana-dac-audio
Params: <None>


Name:   allo-piano-dac-pcm512x-audio
Info:   Configures the Allo Piano DAC (2.0/2.1) audio cards.
        (NB. This initial support is for 2.0 channel audio ONLY! ie. stereo.
        The subwoofer outputs on the Piano 2.1 are not currently supported!)
Load:   dtoverlay=allo-piano-dac-pcm512x-audio,<param>
Params: 24db_digital_gain       Allow gain to be applied via the PCM512x codec
                                Digital volume control.
                                (The default behaviour is that the Digital
                                volume control is limited to a maximum of
                                0dB. ie. it can attenuate but not provide
                                gain. For most users, this will be desired
                                as it will prevent clipping. By appending
                                the 24db_digital_gain parameter, the Digital
                                volume control will allow up to 24dB of
                                gain. If this parameter is enabled, it is the
                                responsibility of the user to ensure that
                                the Digital volume control is set to a value
                                that does not result in clipping/distortion!)


Name:   allo-piano-dac-plus-pcm512x-audio
Info:   Configures the Allo Piano DAC (2.1) audio cards.
Load:   dtoverlay=allo-piano-dac-plus-pcm512x-audio,<param>
Params: 24db_digital_gain       Allow gain to be applied via the PCM512x codec
                                Digital volume control.
                                (The default behaviour is that the Digital
                                volume control is limited to a maximum of
                                0dB. ie. it can attenuate but not provide
                                gain. For most users, this will be desired
                                as it will prevent clipping. By appending
                                the 24db_digital_gain parameter, the Digital
                                volume control will allow up to 24dB of
                                gain. If this parameter is enabled, it is the
                                responsibility of the user to ensure that
                                the Digital volume control is set to a value
                                that does not result in clipping/distortion!)
        glb_mclk                This option is only with Kali board. If enabled,
                                MCLK for Kali is used and PLL is disabled for
                                better voice quality. (default Off)


Name:   anyspi
Info:   Universal device tree overlay for SPI devices

        Just specify the SPI address and device name ("compatible" property).
        This overlay lacks any device-specific parameter support!

        For devices on spi1 or spi2, the interfaces should be enabled
        with one of the spi1-1/2/3cs and/or spi2-1/2/3cs overlays.

        Examples:
        1. SPI NOR flash on spi0.1, maximum SPI clock frequency 45MHz:
            dtoverlay=anyspi:spi0-1,dev="jedec,spi-nor",speed=45000000
        2. MCP3204 ADC on spi1.2, maximum SPI clock frequency 500kHz:
            dtoverlay=anyspi:spi1-2,dev="microchip,mcp3204"
Load:   dtoverlay=anyspi,<param>=<val>
Params: spi<n>-<m>              Configure device at spi<n>, cs<m>
                                (boolean, required)
        dev                     Set device name to search compatible module
                                (string, required)
        speed                   Set SPI clock frequency in Hz
                                (integer, optional, default 500000)


Name:   apds9960
Info:   Configures the AVAGO APDS9960 digital proximity, ambient light, RGB and
        gesture sensor
Load:   dtoverlay=apds9960,<param>=<val>
Params: gpiopin                 GPIO used for INT (default 4)
        noints                  Disable the interrupt GPIO line.


Name:   applepi-dac
Info:   Configures the Orchard Audio ApplePi-DAC audio card
Load:   dtoverlay=applepi-dac
Params: <None>


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 3000000)
        trim                    Fine tuning of the internal capacitance
                                arrays (0=+0pF, 15=+4.5pF, default 15)


Name:   audioinjector-addons
Info:   Configures the audioinjector.net audio add on soundcards
Load:   dtoverlay=audioinjector-addons,<param>=<val>
Params: non-stop-clocks         Keeps the clocks running even when the stream
                                is paused or stopped (default off)


Name:   audioinjector-isolated-soundcard
Info:   Configures the audioinjector.net isolated soundcard
Load:   dtoverlay=audioinjector-isolated-soundcard
Params: <None>


Name:   audioinjector-ultra
Info:   Configures the audioinjector.net ultra soundcard
Load:   dtoverlay=audioinjector-ultra
Params: <None>


Name:   audioinjector-wm8731-audio
Info:   Configures the audioinjector.net audio add on soundcard
Load:   dtoverlay=audioinjector-wm8731-audio
Params: <None>


Name:   audiosense-pi
Info:   Configures the audiosense-pi add on soundcard
        For more information refer to
        https://gitlab.com/kakar0t/audiosense-pi
Load:   dtoverlay=audiosense-pi
Params: <None>


Name:   audremap
Info:   Switches PWM sound output to GPIOs on the 40-pin header
Load:   dtoverlay=audremap,<param>=<val>
Params: swap_lr                 Reverse the channel allocation, which will also
                                swap the audio jack outputs (default off)
        enable_jack             Don't switch off the audio jack output
                                (default off)
        pins_12_13              Select GPIOs 12 & 13 (default)
        pins_18_19              Select GPIOs 18 & 19


Name:   balena-fin
Info:   Overlay that enables WiFi, Bluetooth and the GPIO expander on the
        balenaFin carrier board for the Raspberry Pi Compute Module 3/3+ Lite.
Load:   dtoverlay=balena-fin
Params: <None>


Name:   bmp085_i2c-sensor
Info:   This overlay is now deprecated - see i2c-sensor
Load:   <Deprecated>


Name:   cma
Info:   Set custom CMA sizes, only use if you know what you are doing, might
        clash with other overlays like vc4-fkms-v3d and vc4-kms-v3d.
Load:   dtoverlay=cma,<param>=<val>
Params: cma-512                 CMA is 512MB (needs 1GB)
        cma-448                 CMA is 448MB (needs 1GB)
        cma-384                 CMA is 384MB (needs 1GB)
        cma-320                 CMA is 320MB (needs 1GB)
        cma-256                 CMA is 256MB (needs 1GB)
        cma-192                 CMA is 192MB (needs 1GB)
        cma-128                 CMA is 128MB
        cma-96                  CMA is 96MB
        cma-64                  CMA is 64MB
        cma-size                CMA size in bytes, 4MB aligned
        cma-default             Use upstream's default value


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)


Name:   dionaudio-loco
Info:   Configures the Dion Audio LOCO DAC-AMP
Load:   dtoverlay=dionaudio-loco
Params: <None>


Name:   dionaudio-loco-v2
Info:   Configures the Dion Audio LOCO-V2 DAC-AMP
Load:   dtoverlay=dionaudio-loco-v2,<param>=<val>
Params: 24db_digital_gain       Allow gain to be applied via the PCM512x codec
                                Digital volume control. Enable with
                                "dtoverlay=hifiberry-dacplus,24db_digital_gain"
                                (The default behaviour is that the Digital
                                volume control is limited to a maximum of
                                0dB. ie. it can attenuate but not provide
                                gain. For most users, this will be desired
                                as it will prevent clipping. By appending
                                the 24dB_digital_gain parameter, the Digital
                                volume control will allow up to 24dB of
                                gain. If this parameter is enabled, it is the
                                responsibility of the user to ensure that
                                the Digital volume control is set to a value
                                that does not result in clipping/distortion!)


Name:   disable-bt
Info:   Disable onboard Bluetooth on Pi 3B, 3B+, 3A+, 4B and Zero W, restoring
        UART0/ttyAMA0 over GPIOs 14 & 15.
        N.B. To disable the systemd service that initialises the modem so it
        doesn't use the UART, use 'sudo systemctl disable hciuart'.
Load:   dtoverlay=disable-bt
Params: <None>


Name:   disable-wifi
Info:   Disable onboard WiFi on Pi 3B, 3B+, 3A+, 4B and Zero W.
Load:   dtoverlay=disable-wifi
Params: <None>


Name:   dpi18
Info:   Overlay for a generic 18-bit DPI display
        This uses GPIOs 0-21 (so no I2C, uart etc.), and activates the output
        2-3 seconds after the kernel has started.
Load:   dtoverlay=dpi18
Params: <None>


Name:   dpi24
Info:   Overlay for a generic 24-bit DPI display
        This uses GPIOs 0-27 (so no I2C, uart etc.), and activates the output
        2-3 seconds after the kernel has started.
Load:   dtoverlay=dpi24
Params: <None>


Name:   draws
Info:   Configures the NW Digital Radio DRAWS Hat

        The board includes an ADC to measure various board values and also
        provides two analog user inputs on the expansion header.  The ADC
        can be configured for various sample rates and gain values to adjust
        the input range.  Tables describing the two parameters follow.

        ADC Gain Values:
            0 = +/- 6.144V
            1 = +/- 4.096V
            2 = +/- 2.048V
            3 = +/- 1.024V
            4 = +/- 0.512V
            5 = +/- 0.256V
            6 = +/- 0.256V
            7 = +/- 0.256V

        ADC Datarate Values:
            0 = 128sps
            1 = 250sps
            2 = 490sps
            3 = 920sps
            4 = 1600sps (default)
            5 = 2400sps
            6 = 3300sps
            7 = 3300sps
Load:   dtoverlay=draws,<param>=<val>
Params: draws_adc_ch4_gain      Sets the full scale resolution of the ADCs
                                input voltage sensor (default 1)

        draws_adc_ch4_datarate  Sets the datarate of the ADCs input voltage
                                sensor

        draws_adc_ch5_gain      Sets the full scale resolution of the ADCs
                                5V rail voltage sensor (default 1)

        draws_adc_ch5_datarate  Sets the datarate of the ADCs 4V rail voltage
                                sensor

        draws_adc_ch6_gain      Sets the full scale resolution of the ADCs
                                AIN2 input (default 2)

        draws_adc_ch6_datarate  Sets the datarate of the ADCs AIN2 input

        draws_adc_ch7_gain      Sets the full scale resolution of the ADCs
                                AIN3 input (default 2)

        draws_adc_ch7_datarate  Sets the datarate of the ADCs AIN3 input

        alsaname                Name of the ALSA audio device (default "draws")


Name:   dwc-otg
Info:   Selects the dwc_otg USB controller driver which has fiq support. This
        is the default on all except the Pi Zero which defaults to dwc2.
Load:   dtoverlay=dwc-otg
Params: <None>


Name:   dwc2
Info:   Selects the dwc2 USB controller driver
Load:   dtoverlay=dwc2,<param>=<val>
Params: dr_mode                 Dual role mode: "host", "peripheral" or "otg"

        g-rx-fifo-size          Size of rx fifo size in gadget mode

        g-np-tx-fifo-size       Size of non-periodic tx fifo size in gadget
                                mode


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


Name:   edt-ft5406
Info:   Overlay for the EDT FT5406 touchscreen on the CSI/DSI I2C interface.
        This works with the Raspberry Pi 7" touchscreen when not being polled
        by the firmware.
        You MUST use either "disable_touchscreen=1" or "ignore_lcd=1" in
        config.txt to stop the firmware polling the touchscreen.
Load:   dtoverlay=edt-ft5406,<param>=<val>
Params: sizex                   Touchscreen size x (default 800)
        sizey                   Touchscreen size y (default 480)
        invx                    Touchscreen inverted x axis
        invy                    Touchscreen inverted y axis
        swapxy                  Touchscreen swapped x y axis


Name:   enc28j60
Info:   Overlay for the Microchip ENC28J60 Ethernet Controller on SPI0
Load:   dtoverlay=enc28j60,<param>=<val>
Params: int_pin                 GPIO used for INT (default 25)

        speed                   SPI bus speed (default 12000000)


Name:   enc28j60-spi2
Info:   Overlay for the Microchip ENC28J60 Ethernet Controller on SPI2
Load:   dtoverlay=enc28j60-spi2,<param>=<val>
Params: int_pin                 GPIO used for INT (default 39)

        speed                   SPI bus speed (default 12000000)


Name:   exc3000
Info:   Enables I2C connected EETI EXC3000 multiple touch controller using
        GPIO 4 (pin 7 on GPIO header) for interrupt.
Load:   dtoverlay=exc3000,<param>=<val>
Params: interrupt               GPIO used for interrupt (default 4)
        sizex                   Touchscreen size x (default 4096)
        sizey                   Touchscreen size y (default 4096)
        invx                    Touchscreen inverted x axis
        invy                    Touchscreen inverted y axis
        swapxy                  Touchscreen swapped x y axis


Name:   fe-pi-audio
Info:   Configures the Fe-Pi Audio Sound Card
Load:   dtoverlay=fe-pi-audio
Params: <None>


Name:   fsm-demo
Info:   A demonstration of the gpio-fsm driver. The GPIOs are chosen to work
        nicely with a "traffic-light" display of red, amber and green LEDs on
        GPIOs 7, 8 and 25 respectively.
Load:   dtoverlay=fsm-demo,<param>=<val>
Params: fsm_debug               Enable debug logging (default off)


Name:   ghost-amp
Info:   An overlay for the Ghost amplifier.
Load:   dtoverlay=ghost-amp,<param>=<val>
Params: fsm_debug               Enable debug logging of the GPIO FSM (default
                                off)


Name:   goodix
Info:   Enables I2C connected Goodix gt9271 multiple touch controller using
        GPIOs 4 and 17 (pins 7 and 11 on GPIO header) for interrupt and reset.
Load:   dtoverlay=goodix,<param>=<val>
Params: interrupt               GPIO used for interrupt (default 4)
        reset                   GPIO used for reset (default 17)


Name:   googlevoicehat-soundcard
Info:   Configures the Google voiceHAT soundcard
Load:   dtoverlay=googlevoicehat-soundcard
Params: <None>


Name:   gpio-fan
Info:   Configure a GPIO pin to control a cooling fan.
Load:   dtoverlay=gpio-fan,<param>=<val>
Params: gpiopin                 GPIO used to control the fan (default 12)
        temp                    Temperature at which the fan switches on, in
                                millicelcius (default 55000)


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 "up".

        invert                  "1" = invert the input (active-low signalling).
                                "0" = non-inverted input (active-high
                                signalling). Default is "1".

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


Name:   gpio-ir-tx
Info:   Use GPIO pin as bit-banged infrared transmitter output.
        This is an alternative to "pwm-ir-tx". gpio-ir-tx doesn't require
        a PWM so it can be used together with onboard analog audio.
Load:   dtoverlay=gpio-ir-tx,<param>=<val>
Params: gpio_pin                Output GPIO (default 18)

        invert                  "1" = invert the output (make it active-low).
                                Default is "0" (active-high).


Name:   gpio-key
Info:   This is a generic overlay for activating GPIO keypresses using
        the gpio-keys library and this dtoverlay. Multiple keys can be
        set up using multiple calls to the overlay for configuring
        additional buttons or joysticks. You can see available keycodes
        at https://github.com/torvalds/linux/blob/v4.12/include/uapi/
        linux/input-event-codes.h#L64
Load:   dtoverlay=gpio-key,<param>=<val>
Params: gpio                    GPIO pin to trigger on (default 3)
        active_low              When this is 1 (active low), a falling
                                edge generates a key down event and a
                                rising edge generates a key up event.
                                When this is 0 (active high), this is
                                reversed. The default is 1 (active low)
        gpio_pull               Desired pull-up/down state (off, down, up)
                                Default is "up". Note that the default pin
                                (GPIO3) has an external pullup
        label                   Set a label for the key
        keycode                 Set the key code for the button


Name:   gpio-no-bank0-irq
Info:   Use this overlay to disable GPIO interrupts for GPIOs in bank 0 (0-27),
        which can be useful for UIO drivers.
        N.B. Using this overlay will trigger a kernel WARN during booting, but
        this can safely be ignored - the system should work as expected.
Load:   dtoverlay=gpio-no-bank0-irq
Params: <None>


Name:   gpio-no-irq
Info:   Use this overlay to disable all GPIO interrupts, which can be useful
        for user-space GPIO edge detection systems.
Load:   dtoverlay=gpio-no-irq
Params: <None>


Name:   gpio-poweroff
Info:   Drives a GPIO high or low on poweroff (including halt). Enabling this
        overlay will prevent the ability to boot by driving GPIO3 low.
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.
        input                   Set if the gpio pin should be configured as
                                an input.
        export                  Set to export the configured pin to sysfs
        timeout_ms              Specify (in ms) how long the kernel waits for
                                power-down before issuing a WARN (default 3000).


Name:   gpio-shutdown
Info:   Initiates a shutdown when GPIO pin changes. The given GPIO pin
        is configured as an input key that generates KEY_POWER events.

        This event is handled by systemd-logind by initiating a
        shutdown. Systemd versions older than 225 need an udev rule
        enable listening to the input device:

                ACTION!="REMOVE", SUBSYSTEM=="input", KERNEL=="event*", \
                        SUBSYSTEMS=="platform", DRIVERS=="gpio-keys", \
                        ATTRS{keys}=="116", TAG+="power-switch"

        Alternatively this event can be handled also on systems without
        systemd, just by traditional SysV init daemon. KEY_POWER event
        (keycode 116) needs to be mapped to KeyboardSignal on console
        and then kb::kbrequest inittab action which is triggered by
        KeyboardSignal from console can be configured to issue system
        shutdown. Steps for this configuration are:

            Add following lines to the /etc/console-setup/remap.inc file:

                # Key Power as special keypress
                keycode 116 = KeyboardSignal

            Then add following lines to /etc/inittab file:

                # Action on special keypress (Key Power)
                kb::kbrequest:/sbin/shutdown -t1 -a -h -P now

            And finally reload configuration by calling following commands:

                # dpkg-reconfigure console-setup
                # service console-setup reload
                # init q

        This overlay only handles shutdown. After shutdown, the system
        can be powered up again by driving GPIO3 low. The default
        configuration uses GPIO3 with a pullup, so if you connect a
        button between GPIO3 and GND (pin 5 and 6 on the 40-pin header),
        you get a shutdown and power-up button. Please note that
        Raspberry Pi 1 Model B rev 1 uses GPIO1 instead of GPIO3.
Load:   dtoverlay=gpio-shutdown,<param>=<val>
Params: gpio_pin                GPIO pin to trigger on (default 3)
                                For Raspberry Pi 1 Model B rev 1 set this
                                explicitly to value 1, e.g.:

                                    dtoverlay=gpio-shutdown,gpio_pin=1

        active_low              When this is 1 (active low), a falling
                                edge generates a key down event and a
                                rising edge generates a key up event.
                                When this is 0 (active high), this is
                                reversed. The default is 1 (active low).

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

                                Note that the default pin (GPIO3) has an
                                external pullup. Same applies for GPIO1
                                on Raspberry Pi 1 Model B rev 1.

        debounce                Specify the debounce interval in milliseconds
                                (default 100)


Name:   hd44780-lcd
Info:   Configures an HD44780 compatible LCD display. Uses 4 gpio pins for
        data, 2 gpio pins for enable and register select and 1 optional pin
        for enabling/disabling the backlight display.
Load:   dtoverlay=hd44780-lcd,<param>=<val>
Params: pin_d4                  GPIO pin for data pin D4 (default 6)

        pin_d5                  GPIO pin for data pin D5 (default 13)

        pin_d6                  GPIO pin for data pin D6 (default 19)

        pin_d7                  GPIO pin for data pin D7 (default 26)

        pin_en                  GPIO pin for "Enable" (default 21)

        pin_rs                  GPIO pin for "Register Select" (default 20)

        pin_bl                  Optional pin for enabling/disabling the
                                display backlight. (default disabled)

        display_height          Height of the display in characters

        display_width           Width of the display in characters


Name:   hdmi-backlight-hwhack-gpio
Info:   Devicetree overlay for GPIO based backlight on/off capability.
        Use this if you have one of those HDMI displays whose backlight cannot