sysupgrade -v --test openwrt-ath79-generic-tplink_tl-wr842n-v1-squashfs-sysupgrade.bin
Device tl-mr3420 not supported by this image
Supported devices: tplink,tl-wr842n-v1
Image check 'fwtool_check_image' failed.
i'll try the -F option and see how it goes.