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Machine Configuration Reference

This document explains the machine configuration files in meta-garg/conf/machine/.

BeagleBone Black (beaglebone-black.conf)

The BeagleBone Black uses a TI AM335x SoC (ARM Cortex-A8).

Header Comments

#@TYPE: Machine
#@NAME: BeagleBone Black
#@DESCRIPTION: Machine configuration for BeagleBone Black (AM335x)

These are metadata comments used by tools like the layer index to describe the machine.

SoC and Architecture

require conf/machine/include/ti-soc.inc
SOC_FAMILY = "ti-am335x"
DEFAULTTUNE = "cortexa8hf-neon"
require conf/machine/include/arm/armv7a/tune-cortexa8.inc
Variable Meaning
require conf/machine/include/ti-soc.inc Pulls in TI-specific SoC defaults from meta-ti
SOC_FAMILY Identifies the SoC family for BSP layer matching
DEFAULTTUNE Compiler tuning: Cortex-A8, hard-float, NEON SIMD
tune-cortexa8.inc Sets GCC flags: -mcpu=cortex-a8 -mfpu=neon -mfloat-abi=hard

Kernel Configuration

PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
PREFERRED_VERSION_linux-yocto = "6.6%"
KERNEL_IMAGETYPE = "zImage"
KERNEL_DEVICETREE = "am335x-boneblack.dtb"
Variable Meaning
PREFERRED_PROVIDER_virtual/kernel Which kernel recipe to use (linux-yocto is the Yocto-maintained kernel)
PREFERRED_VERSION_linux-yocto Pin to 6.6.x LTS kernel (% is wildcard)
KERNEL_IMAGETYPE zImage = compressed ARM 32-bit kernel image
KERNEL_DEVICETREE Device tree blob describing the BeagleBone Black hardware

Bootloader

UBOOT_MACHINE = "am335x_evm_defconfig"
SPL_BINARY = "MLO"
UBOOT_SUFFIX = "img"
Variable Meaning
UBOOT_MACHINE U-Boot defconfig to build (AM335x EVM covers BeagleBone)
SPL_BINARY Secondary Program Loader filename (first-stage bootloader loaded by ROM)
UBOOT_SUFFIX U-Boot binary extension (produces u-boot.img)

Boot flow: ROM → MLO (SPL) → u-boot.img → zImage + DTB

Machine Features

MACHINE_FEATURES = "usbgadget usbhost vfat ext2 screen alsa ethernet wifi"
MACHINE_EXTRA_RRECOMMENDS = "kernel-modules kernel-devicetree"
Feature What it enables
usbgadget USB device mode (BeagleBone can appear as USB device)
usbhost USB host mode (connect USB devices)
vfat FAT filesystem support (for boot partition)
ext2 ext2/3/4 filesystem support
screen Display/framebuffer support
alsa Audio support
ethernet Wired networking
wifi Wireless networking

MACHINE_EXTRA_RRECOMMENDS installs kernel modules and device tree into the image.

Serial Console & Image

SERIAL_CONSOLES = "115200;ttyS0"
IMAGE_FSTYPES = "tar.xz wic wic.bmap"
WKS_FILE = "beaglebone-yocto.wks"
Variable Meaning
SERIAL_CONSOLES Baud rate and serial device for getty
IMAGE_FSTYPES Output formats: tarball, WIC disk image, bmap for fast flashing
WKS_FILE Wic kickstart file defining partition layout

Raspberry Pi 5 (raspberrypi5.conf)

The Raspberry Pi 5 uses a BCM2712 SoC (ARM Cortex-A76, quad-core).

Architecture

DEFAULTTUNE = "cortexa76"
require conf/machine/include/arm/armv8-2a/tune-cortexa76.inc
Variable Meaning
DEFAULTTUNE Compiler tuning for Cortex-A76 (ARMv8.2-A, 64-bit)
tune-cortexa76.inc Sets GCC flags for A76: -mcpu=cortex-a76 with crypto extensions

The RPi5 is significantly more powerful than the BeagleBone new_text64-bit, out-of-order, superscalar.

Kernel Configuration

PREFERRED_PROVIDER_virtual/kernel = "linux-yocto"
PREFERRED_VERSION_linux-yocto = "6.6%"
KERNEL_IMAGETYPE = "Image"
KERNEL_DEVICETREE = "broadcom/bcm2712-rpi-5-b.dtb"
Variable Meaning
KERNEL_IMAGETYPE Image = uncompressed AArch64 kernel (RPi firmware handles decompression)
KERNEL_DEVICETREE BCM2712 device tree for RPi 5 Model B

Bootloader

UBOOT_MACHINE = "rpi_arm64_defconfig"
RPI_USE_U_BOOT = "1"
ENABLE_UART = "1"
DISABLE_OVERSCAN = "1"
Variable Meaning
UBOOT_MACHINE U-Boot config for RPi 64-bit
RPI_USE_U_BOOT Use U-Boot instead of direct kernel boot from RPi firmware
ENABLE_UART Enable serial console on GPIO pins
DISABLE_OVERSCAN Disable TV overscan compensation (for monitors)

Boot flow: RPi Firmware (GPU) → U-Boot → Image + DTB

Note: The Raspberry Pi has a unique boot process where the VideoCore GPU loads firmware from the SD card's FAT partition, which then loads U-Boot (or the kernel directly).

Machine Features

MACHINE_FEATURES = "usbhost wifi bluetooth alsa screen ethernet"
MACHINE_EXTRA_RRECOMMENDS = "kernel-modules kernel-devicetree linux-firmware-rpidistro-bcm43455"

The linux-firmware-rpidistro-bcm43455 package provides WiFi/BT firmware blobs needed for the onboard wireless chip.

Serial Console & Image

SERIAL_CONSOLES = "115200;ttyAMA10"
IMAGE_FSTYPES = "tar.xz rpi-sdimg wic wic.bmap"
Variable Meaning
SERIAL_CONSOLES ttyAMA10 is the PL011 UART exposed on GPIO 14/15 on RPi5
rpi-sdimg RPi-specific SD card image format with boot partition

Key Differences Summary

Aspect BeagleBone Black Raspberry Pi 5
Architecture ARMv7-A (32-bit) ARMv8.2-A (64-bit)
CPU Cortex-A8, single core Cortex-A76, quad core
Kernel image zImage (compressed) Image (uncompressed)
Boot flow ROM → MLO → U-Boot GPU FW → U-Boot
Serial port ttyS0 ttyAMA10
WiFi firmware External (cape) Onboard (needs blob)
Image format wic rpi-sdimg / wic

Adding a New Machine

To add support for another board:

  1. Create meta-garg/conf/machine/<machine-name>.conf
  2. Set DEFAULTTUNE and include the appropriate tune file
  3. Configure kernel, bootloader, and device tree
  4. Define MACHINE_FEATURES for available hardware
  5. Set SERIAL_CONSOLES and IMAGE_FSTYPES
  6. Add the BSP layer to bblayers.conf
  7. Create a manifest XML if using repo