To access the shell, type q then a return to get the player to go to a shell. Keep in mind that you should be able to see text as the unit boots up through the serial port. If you don't see it, something else is misconfigured. Your terminal program needs to be set to 115200,8,N,1 and no handshaking.

And switching back and forth between the developer and consumer works fine, at least it did in 9b.

Reg 1640, 6gb Blue empeg-car mark 1. SN 00359