OpenWrt support for Zyxel PMG5617GA, first GPON support !?

So far, interrupting the boot process at

Hit any key to stop autoboot:  5

renders the following output:

ZHAL>

An typing a '?' will yeld:

ATEN    x[,y]         set BootExtension Debug Flag (y=password)
ATSE    x             show the seed of password generator
ATDC                  disable check model mechanism
ATSH                  dump manufacturer related data in ROM
ATRT    [x,y,z,u]     RAM read/write test (x=level, y=start addr, z=end addr, u=iterations)
ATGO                  boot up whole system
ATSR    [x]           system reboot
ATUR    x[,y]         upgrade RAS image (filename, partition number)

This looks a lot like OpenWrt style U-Boot so it might be a modified bootloader. Know any magic commands to throw at it to gain some insight of its Flash structure? All i know so far is that its size is 0x8000000.