Hello,
I just disassembled my W6 and found ... a serial port and U-boot (see attached picture).
The env-print:
isvp_t21# env print
baudrate=115200
bootargs=console=ttyS1,115200n8 mem=43M@0x0 rmem=21M@0x2B00000 init=/linuxrc rootfstype=squashfs root=/dev/mtdblock2 rw...