Currently almost of all RK3188 based devices including the Radxa Rock use proprietary bootloader from Rockchip. Unfortunately Rockchip does not provide the source code for the bootloader.
Some(few?) RK3188 devices use U-Boot based bootloader.
The bootloaders main task is to:
- Load and verify the parameter
- Load and run the command in misc partition
- Load, verify, and boot the kernel and ramdisk from kernel, boot, or recovery partition.
- Communicate with the host PC to download the image/firmware for upgrading
The proprietary bootloader of the Radxa Rock can be downloaded from this address:
The analysis of the bootloader is done by sarg. You can contact sarg on IRC on the channel #linux-rockchip if you are interested. You can find the details here:
You can find more information on sargs work here although the article is in Chinese.