ormus-solutions/libreembed-claude-code/embedded-linux-patterns

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

# 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

# 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

/* 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>;
};

# Makefile for out-of-tree kernel module
KDIR ?= /lib/modules/$(shell uname -r)/build
 
obj-m += mydriver.o
mydriver-objs := mydriver_core.o mydriver_spi.o
 
all:
	$(MAKE) -C $(KDIR) M=$(PWD) modules
 
clean:
	$(MAKE) -C $(KDIR) M=$(PWD) clean
 
# Cross-compile:
# make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KDIR=/path/to/kernel

static ssize_t temperature_show(struct device *dev,
                                 struct device_attribute *attr, char *buf)
{
    struct mydev_priv *priv = dev_get_drvdata(dev);
    int32_t temp_mC = mydev_read_temperature(priv);
    return sysfs_emit(buf, "%d\n", temp_mC);
}
static DEVICE_ATTR_RO(temperature);
 
static struct attribute *mydev_attrs[] = {
    &dev_attr_temperature.attr,
    NULL,
};
ATTRIBUTE_GROUPS(mydev);
 
/* Add to platform_driver: */
.driver = {
    .name        = "mydev",
    .dev_groups  = mydev_groups,
    .of_match_table = mydev_of_match,
},

# Test ARM userspace binary on x86 host (requires binfmt_misc + qemu-user)
apt install qemu-user-static
qemu-arm-static -L /usr/arm-linux-gnueabihf ./myapp
 
# Full system emulation with Yocto image:
runqemu qemuarm nographic core-image-minimal
 
# Boot custom kernel + rootfs:
qemu-system-arm \
  -M virt -cpu cortex-a15 \
  -kernel zImage \
  -dtb virt.dtb \
  -initrd rootfs.cpio.gz \
  -append "console=ttyAMA0 root=/dev/ram" \
  -nographic