The valid SHA256 hashes for the bootrom are:
cbd05621d738d5a913512b63846a9d45b408ab88403306e1740de05f0304ed63 32768
and 237a3303ac6c70c084a8c51aa58b89becc3f951970a02fd92d15b8f15f2ab4cf 28624 bytes length (last string location).
The easiest way of dumping it is to have latest U-Boot installed, then, with inserted empty sdcard where loss of the data on it will not cause any trouble type
mmc write 2a000000 0 40 (NOTE 40 not 8000: the mmc command accepts numbers of 512B blocks, not bytes!!) to write entire bootrom to sdcard, then eject it and insert into any Linux box and read first 32K blocks from it’s corresponding block device.
I’m work in progress with full decompilation of it as part of my RISC-V learning process (8147 insns, 148+ observable functions), but currently it is stuck due to IRL problems.
@Michael.Zhu is there any inside info about will be ever bootrom source code released? For example, Milk-V project and SG2042 manufacturers already released their ZSBL source.
EDIT correction of last observable meaningful byte location to 0x6fd0 (28624) thanks to @mzs