beagle — RTEMS User Manual 5.4-rc2 (21st August 2026) documentation

# beagle

This BSP supports four variants, beagleboardorig, beagleboardxm, beaglebonewhite and beagleboneblack. The basic hardware initialization is not performed by the BSP. A boot loader with device tree support must be used to start the BSP, e.g., U-Boot.

TODO(These drivers are present but not documented yet):

> - Clock driver.

> - Network Interface Driver.

> - SDcard driver.

> - GPIO Driver.

> - Console driver.

> - PWM Driver.

> - RTC driver.

## Boot via U-Boot

To boot via uboot, the ELF must be converted to a U-Boot image like below:

    arm-rtems5-objcopy hello.exe -O binary app.bin
    gzip -9 app.bin
    mkimage -A arm -O linux -T kernel -a 0x80000000 -e 0x80000000 -n RTEMS -d app.bin.gz rtems-app.img

## Getting the Device Tree Blob

The Device Tree Blob (DTB) is needed to load the device tree while starting up the kernel. We build the dtb from the FreeBSD source matching the commit hash from the libbsd HEAD of freebsd-org. For example if the HEAD is at “19a6ceb89dbacf74697d493e48c388767126d418” Then the right Device Tree Source (DTS) file is: https://github.com/freebsd/freebsd/blob/19a6ceb89dbacf74697d493e48c388767126d418/sys/gnu/dts/arm/am335x-boneblack.dts

Please refer to the Device Tree to know more about building and applying the Device Trees.

## Writing the uEnv.txt file

The uEnv.txt file is needed to set any environment variable before the kernel is loaded. Each line is a u-boot command that the uboot will execute during start up.

Add the following to a file named uEnv.txt:

    setenv bootdelay 5
    uenvcmd=run boot
    boot=fatload mmc 0 0x80800000 rtems-app.img ; fatload mmc 0 0x88000000 am335x-boneblack.dtb ; bootm 0x80800000 - 0x88000000

## I2C Driver

The Beagle has the i2c-0 device registered at initialization. For registering i2c-1 and i2c-2 `bbb_register_i2c_1()` and `bbb_register_i2c_2()` wrapper functions are respectively used.

For registering an I2C device with a custom path (say /dev/i2c-3) the function `am335x_i2c_bus_register()` has to be used.

The function prototype is given below:

    int am335x_i2c_bus_register(
    const char         *bus_path,
    uintptr_t           register_base,
    uint32_t            input_clock,
    rtems_vector_number irq
    );

## SPI Driver

The SPI device /dev/spi-0 can be registered with `bbb_register_spi_0()`

For registering with a custom path, the `bsp_register_spi()` can be used.

The function prototype is given below:

    rtems_status_code bsp_register_spi(
       const char         *bus_path,
       uintptr_t           register_base,
       rtems_vector_number irq
    );