https://github.com/lindenis-org/lindenis-v853-lichee-brandy-2.0-spl-pub

you need remake checksum, after modify image.

https://github.com/nminaylov/F1C100s_projects/blob/master/tools/mksunxi/mksunxi.c

reference:

https://github.com/lindenis-org/lindenis-v853-lichee-brandy-2.0-spl-pub/blob/master/include/private_boot0.h

allwinner have some tools use for modify this:

https://github.com/lindenis-org/lindenis-v853-tools

some opensource reference:

boot0 load boot-package:

https://github.com/lindenis-org/lindenis-v853-lichee-brandy-2.0-spl-pub/blob/d36b228278e654d7d7bfa2f5f777311b6d9dc61b/nboot/main/boot0_main.c#LL101C15-L101C15

boot0 load_package() function source code:

https://github.com/szemzoa/sun8iw20_spl/blob/aedc18e734ecc71262fb64f962f485a12e56981c/nboot/load_image_mmc/load_image_sdmmc.c#L157

boot0 load_toc1_from_sdmmc() function source code:

https://github.com/szemzoa/sun8iw20_spl/blob/aedc18e734ecc71262fb64f962f485a12e56981c/nboot/load_image_mmc/load_image_sdmmc.c#LL113C4-L113C4

v85x will load boot-package from this offset in sdcard:

https://github.com/lindenis-org/lindenis-v853-lichee-brandy-2.0-spl-pub/blob/d36b228278e654d7d7bfa2f5f777311b6d9dc61b/include/spare_head.h#L64

toc1 header struct:

https://github.com/szemzoa/sun8iw20_spl/blob/aedc18e734ecc71262fb64f962f485a12e56981c/nboot/load_image_mmc/load_image_sdmmc.c#LL119C9-L119C9

https://github.com/lindenis-org/lindenis-v853-lichee-brandy-2.0-spl-pub/blob/d36b228278e654d7d7bfa2f5f777311b6d9dc61b/include/private_toc.h#L58

boot0 load_image() function source code:

https://github.com/szemzoa/sun8iw20_spl/blob/aedc18e734ecc71262fb64f962f485a12e56981c/nboot/main/load_image.c#L31

how to make toc1:

https://linux-sunxi.org/Allwinner_Nezha#BSP_boot0_SPL

https://fedoraproject.org/wiki/Architectures/RISC-V/Allwinner/zh-cn#%E5%88%9B%E5%BB%BA_u-boot.toc1

https://github.com/smaeul/u-boot/blob/d1-wip/tools/sunxi_toc1.c

I make a project, use buildroot generate bootable v85x bootimage:

https://github.com/newluhux/buildroot_aw_v85x

/* check sysctl, allwinner sucks, no register guide for this*/
/* check allwinner sid */
if (read32(0x030060a0) == 0) {
	if (read(0x03006200 & 0xFFFF) != 0) {
		pr_emerg("bootinfo error1\n");
		return 1;
	}
}