Just making sure. Is it JTAG or a serial port?
Would be handy if there was a serial port?
We can also start to help if you want to try to upload more info to help and/or start work yourself on getting this in?
What's your development experience? It sounds like the shell you have isn't that featured and/or is locked down?
edit: your post above looks to be a locked down not a normal shell.
Can you break into a standard root shell from that?
Anyway here's quoting another thread where I posted steps to start adding a device:
Finally. Doing a binwalk and/or exploring the normal firmware image you download from the manufacturer's site. And/or find the GPL source dump from TP link for example if available?
edit:
There's code for er7206? I can't find er7212?