As it turned out, some of new MediaTek based TP-Link devices use value
from field at 0x3c offset in version 3 of TP-Link header to specify
"Additional Hardware Version".
Value from this field is validated during regular (GUI) firmware upgrade
on devices like TL-WR840N v4 or TL-WR841N v13. If it's zero (based on
some tests, it seems that firmware will accept anything != 0), errors
like below are printed on console and upgrade fails:
[ rsl_sys_updateFirmware ] 2137: Firmware Additional HardwareVersion
check failed
[ rdp_updateFirmware ] 345: perror:4506
Signed-off-by: Piotr Dymacz <pepe2k@gmail.com>
4b35e174ca