Place `u-boot-sunxi-with-spl.bin` here before running the workflow.
The existing TFTP server (`serverip`) must serve this directory as its root.
Checkout alone does not publish files over TFTP.

The workflow clears stale `filesize`, requires a successful TFTP transfer,
and checks hexadecimal `filesize` against both the transfer count and local
file size (32 through 0x200000 bytes). It compares the first 32 RAM bytes
with the local file, probes SPI flash, writes at offset 0, reads back to
0x42800000 and compares the full transferred length with `cmp.b`.

No erase, reboot or saveenv command is issued. Any failed or unverified
command stops execution; flash writes are never automatically retried.