4.31. Allwinner sunxi¶
4.31.1. Boot process¶
On power-up Allwinner SoC starts in boot ROM, aka BROM, which will search for a bootable image (eGON header): first from the SD card, then from eMMC. If no image is found then the boot ROM will enter into FEL mode that can be used for programming and recovery through USB.
Some board may have a button to enter FEL mode at startup. If not, another way to enter FEL mode is to not have a valid bootable eGON image, this can be achieved by erasing existing eGON image headers.
Note
Currently Barebox cannot boot directly on Allwinner sunxi SoC and can only be used as a secondary bootloader, requiring u-boot to initialize the SDRAM controller and starting the TF-A and optionally Crust.
4.31.2. Building barebox second stage¶
The generic barebox-dt-2nd.img armv8 image should enable all the needed
drivers.
To build the image do:
export ARCH=arm CROSS_COMPILE=aarch64-linux-gnu-
make multi_v8_defconfig
make
4.31.3. Installing barebox second stage¶
Copy the built barebox-dt-2nd.img image into the first fat partition
of the boot medium.
# mount /dev/sdX1 /mnt/${mount_dir}
# cp ${build_dir}/images/barebox-dt-2nd.img /mnt/${mount_dir}
# umount /mnt/${mount_dir}
4.31.4. Booting barebox from U-Boot¶
Currently Barebox can only be started as a second stage, and relies on U-Boot for the SDRAM initialisation and to start the TF-A.
# on u-boot console, `mmc 0:1` is the first partition on the sd card
fatload mmc 0:1 0x42000000 barebox-dt-2nd.img
fatload mmc 0:1 0x44000000 dtbs-lts/allwinner/sun50i-a64-pine64-plus.dtb
booti 0x42000000 - 0x44000000
Note
A FIT image might be built and used instead of directly using the barebox-dt-2nd.img, this hasn’t been tested yet, but using a FIT image sound like a better option.
See also the general documentation on Starting barebox.
4.31.5. Building Arm Trusted Firmware (TF-A)¶
Note
This step is currently only needed when building U-Boot. This step is also documented in U-Boot documention.
Boards using a 64-bit Soc (A64, H5, H6, H616, R329) require the BL31 stage of the Arm Trusted Firmware-A firmware. This provides the reference implementation of secure software for Armv8-A, offering PSCI and SMCCC services. Allwinner support is fully mainlined. To build bl31.bin:
git clone https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git
cd trusted-firmware-a
make CROSS_COMPILE=aarch64-linux-gnu- PLAT=sun50i_a64 DEBUG=1
cp build/sun50i_a64/debug/bl31.bin ${barebox_dir}/firmware/sun50i-a64-bl31.bin
The target platform (PLAT=) for A64 and H5 SoCs is sun50i_a64, for the H6
sun50i_h6, for the H616 sun50i_h616, and for the R329 sun50i_r329.
4.31.6. Building U-Boot image¶
Please refere to the relevant U-Boot build documentation (or /doc/board/allwinner/sunxi.rst in u-boot src tree).
4.31.7. Installing the first stage bootloader¶
4.31.7.1. Installing on a (micro-) SD card¶
The bootable image, a eGON header followed by the actual image, must be located at the fixed offset of 8192 bytes (8KB) from the start of the disk (sector 16).
# copy the bootable fsbl image (including eGON header) into disk sdX
dd if=${fsbl.img} of=/dev/sdX bs=512 seek=16
