4.5. Broadcom BCM283x¶
4.5.1. Raspberry Pi¶
Prepare an SD or microSD card with a FAT filesystem of at least 30 MB in size.
Download the Raspberry Pi firmware (120 MB), unzip it, and copy the contents of the
boot/folder to your card.
make rpi_defconfig; maketo build barebox. This will create the following images:
images/barebox-raspberry-pi-1.imgfor the BCM2835/ARM1176JZF-S (Raspberry Pi 1, Raspberry Pi Zero)
images/barebox-raspberry-pi-2.imgfor the BCM2836/CORTEX-A7 (Raspberry Pi 2)
images/barebox-raspberry-pi-3.imgfor the BCM2837/CORTEX-A53 (Raspberry Pi 3)
images/barebox-raspberry-pi-cm3.imgfor the BCM2837/CORTEX-A53 (Raspberry Pi CM3)
Copy the respective image for your model to your SD card and name it
images/barebox-dt-2nd.imgcan be used as single bootloader for all supported 32-bit boards. In this case the device tree supplied by the video core is directly used by barebox to probe. The device trees in
arch/arm/dts/*.dtbwill need to be renamed for alignment with the naming scheme expected by the videocore.
Create a text file
config.txton 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.)
Connect to board’s UART (115200 8N1); Use PIN6 (GND), PIN8 (UART_TX), PIN10 (UART_RX) pins.
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 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: