[E3-hacking] PBL & running arbitrary code

[David Given]

On Sun, 2005-03-13 at 15:42 +0000, Matt Evans wrote:
[...]
> Yep, the case was discarded long ago.  So this sounds interesting - I 
> thought all units had the smartmedia slot.  Mine certainly does - but I 
> have the older psion5-style keyboard model.  Does yours still have a 
> smart/card/ slot on the right too?

Yes. I actually rather wanted the SMC socket, and the cold-flesh
keyboard is pretty dire. I *suppose* it might be possible to solder on a
third-party SMC socket but I don't think my soldering skills are up to
it. Just have to make do with USB.

[...]
> Something that was unclear in your previous emails was the cable that 
> you were using - it sounded like it was direct RS232 plug to a 3.5mm 
> jack with no voltage conversion?  This didn't work for me.

Ah, I thought you said it *did* work... hopefully I haven't buggered the
UART.

I experimented with a voltmeter, and I'm seeing just under 5V on RX and
TX coming from the E2, which matches what you said. Alas, I don't have a
scope.

Hmm... TTL uses 0V for 0, 5V for 1. RS232 uses >+3V for 0 and <-3V for
1. Now, if the E2's UART is behaving sensibly, and is suitably buffered
so that I haven't fried it, it might be possible to con it into
responding to the RS232 signals by sending a suitably mutated signal.
Basically, I'd need to send ~0x1B = 0xE4, with an inverted stop bit...
but the E2 wouldn't be able to reply, because the TTL 0V signals that
it's sending would be ignored by the PC's UART. Blast.

I could probably rig up a software UART through the parallel port, if I
had one. (Shuttle box. I'm trying to scrounge up the appropriate header,
but it's had work.)

[...]
> I don't know your 
> level of electronics knowledge but if I can help just ask.

I'm mostly a software guy; I have some soldering skills, but they're not
great. I can rig up a line driver on breadboard easily enough, but
getting a 5V signal that's suitable non-floating might be an issue...

I actually have a ludicrous idea that might help; will report back
later.

-- 
+- David Given --McQ-+ "Working with Unix is like wrestling a worthy
|  dg@cowlark.com    | opponent. Working with Windows is like attacking a
| (dg@tao-group.com) | small whining child who is carrying a .38." ---
+- www.cowlark.com --+ Nancy Lebovitz