Optional build configuration

There are a set of ways in which a user can influence different parameters of the build. We list here the ones that are closely related to this BSP or specific to it. For the rest please check: http://www.yoctoproject.org/docs/latest/ref-manual/ref-manual.html

Compressed deployed files

  1. Overwrite IMAGE_FSTYPES in local.conf

    • IMAGE_FSTYPES = "tar.bz2 ext3.xz"

  2. Overwrite SDIMG_ROOTFS_TYPE in local.conf

    • SDIMG_ROOTFS_TYPE = "ext3.xz"

Accommodate the values above to your own needs (ex: ext3 / ext4).

GPU memory

  • GPU_MEM: GPU memory in megabyte. Sets the memory split between the ARM and GPU. ARM gets the remaining memory. Min 16. Default 64.

  • GPU_MEM_256: GPU memory in megabyte for the 256MB Raspberry Pi. Ignored by the 512MB RP. Overrides gpu_mem. Max 192. Default not set.

  • GPU_MEM_512: GPU memory in megabyte for the 512MB Raspberry Pi. Ignored by the 256MB RP. Overrides gpu_mem. Max 448. Default not set.

  • GPU_MEM_1024: GPU memory in megabyte for the 1024MB Raspberry Pi. Ignored by the 256MB/512MB RP. Overrides gpu_mem. Max 944. Default not set.

See: https://www.raspberrypi.com/documentation/computers/config_txt.html#memory-options

VC4

By default, each machine uses vc4 for graphics. This will in turn sets mesa as provider for gl libraries. DISABLE_VC4GRAPHICS can be set to 1 to disable this behaviour falling back to using userland. Be aware that userland has not support for 64-bit arch. If you disable vc4 on a 64-bit Raspberry Pi machine, expect build breakage.

Add purchased license codecs

To add your own licenses use variables KEY_DECODE_MPG2 and KEY_DECODE_WVC1 in local.conf. Example:

KEY_DECODE_MPG2 = "12345678"
KEY_DECODE_WVC1 = "12345678"

You can supply more licenses separated by comma. Example:

KEY_DECODE_WVC1 = "0x12345678,0xabcdabcd,0x87654321"

See: https://www.raspberrypi.com/documentation/computers/config_txt.html#licence-key-and-codec-options

Disable overscan

By default the GPU adds a black border around the video output to compensate for TVs which cut off part of the image. To disable this set this variable in local.conf:

DISABLE_OVERSCAN = "1"

Disable splash screen

By default a rainbow splash screen is shown after the GPU firmware is loaded. To disable this set this variable in local.conf:

DISABLE_SPLASH = "1"

Boot delay

The Raspberry Pi waits a number of seconds after loading the GPU firmware and before loading the kernel. By default it is one second. This is useful if your SD card needs a while to get ready before Linux is able to boot from it. To remove (or adjust) this delay set these variables in local.conf:

BOOT_DELAY = "0"
BOOT_DELAY_MS = "0"

Set overclocking options

The Raspberry Pi can be overclocked. As of now overclocking up to the “Turbo Mode” is officially supported by the Raspberry Pi and does not void warranty. Check the config.txt for a detailed description of options and modes. The following variables are supported in local.conf: ARM_FREQ, GPU_FREQ, CORE_FREQ, SDRAM_FREQ and OVER_VOLTAGE.

Example official settings for Turbo Mode in Raspberry Pi 2:

ARM_FREQ = "1000"
CORE_FREQ = "500"
SDRAM_FREQ = "500"
OVER_VOLTAGE = "6"

See: https://www.raspberrypi.com/documentation/computers/config_txt.html#overclocking-options

HDMI and composite video options

The Raspberry Pi can output video over HDMI or SDTV composite (the RCA connector). By default the video mode for these is autodetected on boot: the HDMI mode is selected according to the connected monitor’s EDID information and the composite mode is defaulted to NTSC using a 4:3 aspect ratio. Check the config.txt for a detailed description of options and modes. The following variables are supported in local.conf: HDMI_FORCE_HOTPLUG, HDMI_DRIVE, HDMI_GROUP, HDMI_MODE, HDMI_CVT, CONFIG_HDMI_BOOST, SDTV_MODE, SDTV_ASPECT and DISPLAY_ROTATE.

Example to force HDMI output to 720p in CEA mode:

HDMI_GROUP = "1"
HDMI_MODE = "4"

See: https://www.raspberrypi.com/documentation/computers/configuration.html#hdmi-configuration

Video camera support with V4L2 drivers

Set this variable to enable support for the video camera (Linux 3.12.4+ required):

VIDEO_CAMERA = "1"

Enable offline compositing support

Set this variable to enable support for dispmanx offline compositing:

DISPMANX_OFFLINE = "1"

This will enable the firmware to fall back to off-line compositing of Dispmanx elements. Normally the compositing is done on-line, during scanout, but cannot handle too many elements. With off-line enabled, an off-screen buffer is allocated for compositing. When scene complexity (number and sizes of elements) is high, compositing will happen off-line into the buffer.

Heavily recommended for Wayland/Weston.

See: http://wayland.freedesktop.org/raspberrypi.html

Enable kgdb over console support

To add the kdbg over console (kgdboc) parameter to the kernel command line, set this variable in local.conf:

ENABLE_KGDB = "1"

Boot to U-Boot

To have u-boot load kernel image, set in your local.conf:

RPI_USE_U_BOOT = "1"

This will select the appropriate image format for use with u-boot automatically. For further customisation the KERNEL_IMAGETYPE and KERNEL_BOOTCMD variables can be overridden to select the exact kernel image type (eg. zImage) and u-boot command (eg. bootz) to be used.

Image with Initramfs

To build an initramfs image:

  • Set this 3 kernel variables (in kernel’s do_configure:prepend in linux-raspberrypi.inc after the line kernel_configure_variable LOCALVERSION “””” )

    • kernel_configure_variable BLK_DEV_INITRD y

    • kernel_configure_variable INITRAMFS_SOURCE “”

    • kernel_configure_variable RD_GZIP y

  • Set the yocto variables (e.g. in local.conf)

    • INITRAMFS_IMAGE = "<name for your initramfs image>"

    • INITRAMFS_IMAGE_BUNDLE = "1"

    • BOOT_SPACE = "1073741"

    • INITRAMFS_MAXSIZE = "315400"

    • IMAGE_FSTYPES_pn-${INITRAMFS_IMAGE} = "${INITRAMFS_FSTYPES}"

Including additional files in the SD card image boot partition

The SD card image class supports adding extra files into the boot partition, where the files are copied from either the image root partition or from the build image deploy directory.

To copy files that are present in the root partition into boot, FATPAYLOAD is a simple space-separated list of files to be copied:

FATPAYLOAD = "/boot/example1 /boot/example2"

To copy files from the image deploy directory, the files should be listed in the DEPLOYPAYLOAD as a space-separated list of entries. Each entry lists a file to be copied, and an optional destination filename can be specified by supplying it after a colon separator.

DEPLOYPAYLOAD = "example1-${MACHINE}:example1 example2"

Files that are to be included from the deploy directory will be produced by tasks that image building task must depend upon, to ensure that the files are available when they are needed, so these component deploy tasks must be added to: RPI_SDIMG_EXTRA_DEPENDS.

RPI_SDIMG_EXTRA_DEPENDS:append = " example:do_deploy"

Enable SPI bus

When using device tree kernels, set this variable to enable the SPI bus:

ENABLE_SPI_BUS = "1"

Enable I2C

When using device tree kernels, set this variable to enable I2C:

ENABLE_I2C = "1"

Furthermore, to auto-load I2C kernel modules set:

KERNEL_MODULE_AUTOLOAD:rpi += "i2c-dev i2c-bcm2708"

Enable PiTFT support

Basic support for using PiTFT screens can be enabled by adding below in local.conf:

  • MACHINE_FEATURES += "pitft"

    • This will enable SPI bus and i2c device-trees, it will also setup framebuffer for console and x server on PiTFT.

NOTE: To get this working the overlay for the PiTFT model must be build, added and specified as well (dtoverlay= in config.txt).

Below is a list of currently supported PiTFT models in meta-raspberrypi, the modelname should be added as a MACHINE_FEATURES in local.conf like below:

MACHINE_FEATURES += "pitft <modelname>"

List of currently supported models:

  • pitft22

  • pitft28r

  • pitft28c

  • pitft35r

Misc. display

If you would like to use the Waveshare “C” 1024×600, 7 inch Capacitive Touch Screen LCD, HDMI interface (http://www.waveshare.com/7inch-HDMI-LCD-C.htm) Rev 2.1, please set the following in your local.conf:

WAVESHARE_1024X600_C_2_1 = "1"

Enable UART

RaspberryPi 0, 1, 2 and CM will have UART console enabled by default.

RaspberryPi 0 WiFi and 3 does not have the UART enabled by default because this needs a fixed core frequency and enable_uart will set it to the minimum. Certain operations - 60fps h264 decode, high quality deinterlace - which aren’t performed on the ARM may be affected, and we wouldn’t want to do that to users who don’t want to use the serial port. Users who want serial console support on RaspberryPi 0 Wifi or 3 will have to explicitly set in local.conf:

ENABLE_UART = "1"

Ref.:

Enable USB Peripheral (Gadget) support

The standard USB driver only supports host mode operations. Users who want to use gadget modules like g_ether should set the following in local.conf:

ENABLE_DWC2_PERIPHERAL = "1"

Enable USB host support

By default in case of the Compute Module 4 IO Board the standard USB driver that usually supports host mode operations is disabled for power saving reasons. Users who want to use the 2 USB built-in ports or the other ports provided via the header extension should set the following in local.conf:

ENABLE_DWC2_HOST = "1"

Set CPUs to be isolated from the standard Linux scheduler

By default Linux will use all available CPUs for scheduling tasks. For real time purposes there can be an advantage to isolating one or more CPUs from the standard scheduler. It should be noted that CPU 0 is special, it is the only CPU available during the early stages of the boot process and cannot be isolated.

The string assigned to this variable may be a single CPU number, a comma separated list (“1,2”), a range(“1-3”), or a mixture of these (“1,3-5”)

ISOLATED_CPUS = "1-2"

Enable Openlabs 802.15.4 radio module

When using device tree kernels, set this variable to enable the 802.15.4 hat:

ENABLE_AT86RF = "1"

See: https://openlabs.co/OSHW/Raspberry-Pi-802.15.4-radio

Enable CAN

In order to use CAN with an MCP2515-based module, set the following variables:

ENABLE_SPI_BUS = "1"
ENABLE_CAN = "1"

In case of dual CAN module (e.g. PiCAN2 Duo), set following variables instead:

ENABLE_SPI_BUS = "1"
ENABLE_DUAL_CAN = "1"

Some modules may require setting the frequency of the crystal oscillator used on the particular board. The frequency is usually marked on the package of the crystal. By default, it is set to 16 MHz. To change that to 8 MHz, the following variable also has to be set:

CAN_OSCILLATOR="8000000"

Tested modules:

Enable infrared

Users who want to enable infrared support, for example for using LIRC (Linux Infrared Remote Control), have to explicitly set in local.conf:

ENABLE_IR = "1"

This will add device tree overlays gpio-ir and gpio-ir-tx to config.txt. Appropriate kernel modules will be also included in the image. By default the GPIO pin for gpio-ir is set to 18 and the pin for gpio-ir-tx is 17. Both pins can be easily changed by modifying variables GPIO_IR and GPIO_IR_TX.

Enable gpio-shutdown

When using device tree kernels, set this variable to enable gpio-shutdown:

ENABLE_GPIO_SHUTDOWN = "1"

This will add the corresponding device tree overlay to config.txt and include the gpio-keys kernel module in the image. If System V init is used, additional mapping is applied to bind the button event to shutdown command. Systemd init should handle the event out of the box.

By default the feature uses gpio pin 3 (except RPi 1 Model B rev 1 enumerates the pin as gpio 1). This conflicts with the I2C bus. If you set ENABLE_I2C to 1 or enabled PiTFT support, or otherwise want to use another pin, use GPIO_SHUTDOWN_PIN to assign another pin. Example using gpio pin 25:

 GPIO_SHUTDOWN_PIN = "25"

Enable One-Wire Interface

One-wire is a single-wire communication bus typically used to connect sensors to the RaspberryPi. The Raspberry Pi supports one-wire on any GPIO pin, but the default is GPIO 4. To enable the one-wire interface explicitly set it in local.conf

ENABLE_W1 = "1"

Once discovery is complete you can list the devices that your Raspberry Pi has discovered via all 1-Wire busses check the interface with this command

ls /sys/bus/w1/devices/

Manual additions to config.txt

The RPI_EXTRA_CONFIG variable can be used to manually add additional lines to the config.txt file if there is not a specific option above for the configuration you need. To add multiple lines you must include \n separators. If double-quotes are needed in the lines you are adding you can use single quotes around the whole string.

For example, to add a comment containing a double-quote and a configuration option:

RPI_EXTRA_CONFIG = ' \n \
    # Raspberry Pi 7\" display/touch screen \n \
    lcd_rotate=2 \n \
    '

Enable Raspberrypi Camera V2

RaspberryPi does not have the unicam device ( RaspberryPi Camera ) enabled by default. Because this unicam device ( bcm2835-unicam ) as of now is used by libcamera opensource. So we have to explicitly set in local.conf.

RASPBERRYPI_CAMERA_V2 = "1"

This will add the device tree overlays imx219 ( RaspberryPi Camera sensor V2 driver ) to config.txt. Also, this will enable adding Contiguous Memory Allocation value in the cmdline.txt.

Ref.:

WM8960 soundcard support

Support for WM8960 based sound cards such as the WM8960 Hi-Fi Sound Card HAT for Raspberry Pi from Waveshare, and ReSpeaker 2 / 4 / 6 Mics Pi HAT from Seeed Studio, can be enabled in local.conf

```conf
MACHINE_FEATURES += "wm8960"
```

You may need to adjust volume and toggle switches that are off by default

```bash
amixer -c1 sset 'Headphone',0 80%,80%
amixer -c1 sset 'Speaker',0 80%,80%
amixer -c1 sset 'Left Input Mixer Boost' toggle
amixer -c1 sset 'Left Output Mixer PCM' toggle
amixer -c1 sset 'Right Input Mixer Boost' toggle
amixer -c1 sset 'Right Output Mixer PCM' toggle
```

Audio capture on ReSpeaker 2 / 4 / 6 Mics Pi HAT from Seeed Studio is very noisy.

Support for RTC devices

The RaspberryPi boards don’t feature an RTC module and the machine configurations provided in this BSP layer have this assumption (until, if at all, some later boards will come with one).

rtc is handled as a MACHINE_FEATURES in the context of the build system which means that if an attached device is provided for which support is needed, the recommended way forward is to write a new machine configuration based on an existing one. Check the documentation for MACHINE_FEATURES_BACKFILL_CONSIDERED for how this is disabled for the relevant machines.

Even when MACHINE_FEATURES is tweaked to include the needed rtc string, make sure that your kernel configuration is supporting the attached device and the device tree is properly tweaked. Also, mind the runtime components that take advantage of your RTC device. You can do that by checking what is included/configured in the build system based on the inclusion of rtc in MACHINE_FEATURES.