embedded-linux-patterns

embedded-linux-patterns

Knowledge Base

Patterns for Yocto, Buildroot, device trees, and kernel modules on ARM SoCs.

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Pattern 1: Yocto Layer and Recipe Hierarchy

Layers (priority, low to high):
  poky/meta                   # Core: glibc, busybox, gcc toolchain
  poky/meta-poky              # Poky distribution configuration
  meta-openembedded/meta-oe   # Extended packages (Python, Qt, etc.)
  meta-raspberrypi            # BSP: kernel, u-boot, machine configs
  meta-myproject              # Project-specific: your app, config

bblayers.conf adds layers. local.conf sets MACHINE, DISTRO, and BB_NUMBER_THREADS.

# Common BitBake operations:
bitbake core-image-minimal          # Build minimal console image
bitbake -s | grep myapp             # Check recipe is found
bitbake myapp -c cleanall && bitbake myapp  # Rebuild from scratch
bitbake myapp -e | grep ^S=         # Show S (source dir) variable
devtool modify myapp                # Unpack source for development
devtool finish myapp meta-myproject # Write changes back to recipe

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Pattern 2: Kernel Configuration Fragment

Instead of editing .config directly, use a config fragment in a .bbappend:

# meta-myproject/recipes-kernel/linux/linux-%.bbappend
FILESEXTRAPATHS:prepend := "${THISDIR}/files:"
SRC_URI += "file://my-features.cfg"

# files/my-features.cfg
CONFIG_CAN=y
CONFIG_CAN_RAW=y
CONFIG_SPI=y
CONFIG_SPI_SPIDEV=y
CONFIG_I2C_CHARDEV=y
# CONFIG_MODULES is not set   ← explicit disable

Apply with: bitbake linux-imx -c menuconfig then bitbake linux-imx -c savedefconfig.

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Pattern 3: Device Tree GPIO and Interrupt Properties

/* GPIO: <&gpioN pin_num active_level> */
/* IRQ:  <&intc GIC_SPI irq_num IRQ_TYPE_EDGE_RISING> */

mysensor@48 {
    compatible = "ti,ads1115";
    reg = <0x48>;

    /* Active-low interrupt from sensor, connected to PA3 */
    interrupt-parent = <&gpioa>;
    interrupts = <3 IRQ_TYPE_EDGE_FALLING>;

    /* Reset GPIO: active low, initially deasserted */
    reset-gpios = <&gpiob 5 GPIO_ACTIVE_LOW>;
};