Where is the bootrom's source code?

Archive Freedom U500
1

hi all,
I found there is some messege before linux boot, like:
CMD0
CMD8
ACMD41
CMD58
CMD16
CMD18
LOADING
BOOT
INIT
CMD0
CMD8
ACMD41
CMD58
CMD16
CMD18
LOADING
BOOT…

i think this need some uart driver.
but in the bootrom/xip/xip.S there is no such string, and no uart driver. Only in bootrom/u500vc707devkit.img binary file has such string.
where is the full boot code(include linker.ld file), how can i build a custom bootrom.img?

thank you!

2

Our project found and successfully modified the boot ROM under bootrom/sdboot/sd.c (source: https://github.com/sifive/freedom/blob/master/bootrom/sdboot/sd.c).