Understanding BPI-R3 boot sequence

[ldelossa]

Hello.

I am currently exploring the BPI-R3 board for a ground-up networking project.

I will essentially be removing any existing bootloader code on the board.

However, im having trouble finding details on the first stage bootloader. I understand I can tell the board which media to expect the second stage bootloader on, but I cant find any details about the format, offset, and any other info, the first stage bootloader expects.

Is this published anywhere? I grabbed the OpenWRT image and explored it a bit, but dont see uboot or any other bootloader there, so im assuming the board comes with uboot flashed to one of the media devices?

Anyway, my goal here to basically rip out any binaries, and begin working on the board from the first stage (hard coded) bootloader and up. How can I get this info? Happy to look at source code if it exists as well.

[ericwoud (Eric W.)]

[Tutorial] Build, customize and use MediaTek open-source U-Boot and ATF

This tutorial will help you to build, use and customize the official u-boot and atf (TF-A) from MediaTek SDK. 1. Source code U-Boot: GitHub - mtk-openwrt/u-boot: "Das U-Boot" Source Tree ATF: GitHub - mtk-openwrt/arm-trusted-firmware: Read-only mirror of Trusted Firmware-A 2. Toolchain This tutorial talks only about the ARM 64-bit platforms. So you need only the aarch64 toolchain. You can use the openwrt toolchain which can be found in staging_dir/toolchain-aarch64_XXXXX You also need dtc t…

[ldelossa]

Thanks ericwoud, will go over this

[frank-w]

There is no code of the first stage bootloader (bootrom) and afaik you cannot change it. Afaik it expects a fixed offset for second stage (bl2) on mmc and tries 4 positions on spi.

Bl2 (except dram calibration) and Bl31 source is available.