Zyxel PMG3000-D20B firmware image files

Creating image files for the Update Software feature in the Zyxel PMG3000-D20B web interface

Create flash dump of mtd2 or mtd3 (Image A / Image B):

dd if=/dev/mtd2 of=/tmp/mtd2

Download flash dump from SFP (e. g. using TFTP).

Download header file (rename to 'header') and add it to flash dump:

cat header mtd2 > firmware.upf

Copy software version string from flash dump to header:

dd if=firmware.upf of=firmware.upf bs=1 skip=632 seek=124 count=32 conv=notrunc

Get CRC32 of firmware.upf:

v=$(cat firmware.upf | gzip | tail -c 8 | head -c 4 | hexdump -e '1/4 "%08x"')

Convert CRC32 to binary and write it to header:

echo -e -n "\x${v:0:2}\x${v:2:2}\x${v:4:2}\x${v:6:2}" | dd of=firmware.upf bs=1 seek=104 conv=notrunc

Change extension to .zip and extract.
.img: raw mtd2 flash dump
.upf: with header