Broadcom BCM283x
================

Raspberry Pi
------------

barebox has support for BCM283x-based Raspberry Pi single board computers.
Support is most extensive for BCM283[567], but barebox can also boot Linux
over SD or Ethernet on the Raspberry Pi 4.

  1. Prepare an SD or microSD card with a FAT filesystem of at least 30 MB in size.

  2. Download the `Raspberry Pi firmware`_ (195 MB), unzip it, and copy the
     contents of the ``boot/`` folder to your card.

  3. Use ``make rpi_defconfig; make`` to build barebox for 32-bit boards or
     ``make rpi_v8a_defconfig; make`` to build barebox for 64-bit.

     ``rpi_defconfig`` will build at least following images:

     - ``images/barebox-raspberry-pi-1.img`` for the BCM2835/ARM1176JZF-S (Raspberry Pi 1, Raspberry Pi Zero)
     - ``images/barebox-raspberry-pi-2.img`` for the BCM2836/CORTEX-A7 (Raspberry Pi 2)
     - ``images/barebox-raspberry-pi-3.img`` for the BCM2837/CORTEX-A53 (Raspberry Pi 3)
     - ``images/barebox-raspberry-pi-cm3.img`` for the BCM2837/CORTEX-A53 (Raspberry Pi CM3)
     - ``images/barebox-raspberry-pi.img``, which is a super set of all the other images,
       including Raspberry Pi 4 32-bit support.

     Copy the respective image for your model to your SD card and name it
     ``barebox.img``.

     For 64-bit, only ``images/barebox-raspberry-pi.img`` will be created, which is usable
     for both Raspberry Pi 3 and Raspberry Pi 4 in 64-bit mode. No support for the Raspberry
     Pi 5 has been contributed yet.

     The ``images/barebox-raspberry-pi.img`` is expected to be the sole image for 32-bit
     also in the future. It contains the device trees of all supported (and enabled) variants
     and determines at runtime what board it runs on and does the right thing.

  4. Create a text file ``config.txt`` on the SD card with the following content::

         kernel=barebox.img
         enable_uart=1

     If you want to use the mini-uart instead of the PL011, you may need to additionally set::

         uart_2ndstage=1

     This is required on boards, like the Raspberry Pi Zero W, that use the mini-uart as the
     primary UART. It is needed on boards like the CM3 as well if the mini-uart is to be used.

     (For more information, refer to the `documentation for config.txt`_.)

  5. Connect to board's UART (115200 8N1);
     Use PIN6 (GND), PIN8 (UART_TX), PIN10 (UART_RX) pins.

  6. Turn board's power on.

VideoCore firmware creates a device tree based on the entries in ``config.txt``. This file is available to the Barebox environment in the file ``/vc.dtb``. For example, to boot a kernel shipped with Raspbian::

    bootm -o /vc.dtb /boot/kernel7.img

VideoCore device tree also contains the kernel command-line that is constructed from ``cmdline.txt`` and other parameters internally determined by the VideoCore firmware. Normally in Barebox this command-line gets overwritten on boot by the Linux bootargs (see :ref:`booting_linux`).

The original command-line from VideoCore device tree is available to the Barebox environment in the ``vc.bootargs`` global variable. For example, to append it to the Linux bootargs::

    global linux.bootargs.vc="$global.vc.bootargs"

.. _Raspberry Pi firmware: https://github.com/raspberrypi/firmware/archive/refs/tags/1.20220331.zip
.. _documentation for config.txt: https://www.raspberrypi.org/documentation/configuration/config-txt/