Hi
Primary bootloader will open tftp server (or maybe that is client) when it fails to check secondary signature and magic ( at the beginning magic DEADBEEF and at the end C0DEF00D).
I think when I was trying some things web update managed to flash secondary when I removed C0DEF00D at the end, but than primary said wrong magic and started tftp server.
Dont't forget that in order to update from primary you need to do TFTP PUT secondary_boot.img command in binary mode ( or maybe the other one).
P.S. if you have 2 different versions of secondary botloader, open them up with hex editor and see that signatures are almost the same, and that difference to me looks like crc32, but I couldn't find from where it is calculated.
P.P.S. could you send me "fileheader.h" from "Story with SX76x config file" so I could create a simple config decrypt tool and put it here.