So, thanks to a late-night-opening Argos, I now have a fairly shiny E2 sitting on my desk. Damned if I can make it do anything useful.
I did have one stroke of luck; while I was rummaging around in my parts boxes looking for a cable to cut up, I came across a cable with a serial plug on one end and a stereo jack on the other --- debris from some long-defunct digital camera. Right pinout, too, AFAICT.
But the most I'm seeing from the E2 is the occasional 00 byte. What my program is doing is sending 0x1B bytes at 9600 8N1, ten times a second, and echoing in hex anything that comes back. I run this and power cycle the E2. What I should be seeing, if I'm understanding how things work, is the E2 respond with 0B 0B 0B... and the boot process should halt.
I enclose the program, in case anyone can spot any stupid mistakes --- serial port programming in Linux is not my forté.
My E2 has V13 software, PBL V3.1 build 1277, and has the cold flesh keyboard. I haven't set it up, it's completely virgin.
How long does it wait at boot time to be prodded? The splash screen is appearing pretty much as soon as I switch on.