[E3-hacking] PBL & running arbitrary code
Fri, 11 Mar 2005 11:13:09 +0000
On 10 Mar 2005, at 22:28, Ralph Corderoy wrote:
> That's good. (I'd explained to Matt that this was what had been
> achieved with the E3; the suspension of its booting while its EXP port
> was being tickled.) Matt, did you achieve this with that exp program
> of interest?
I didn't - was just sending ESC codes through some dumb mac terminal
program; I'll be trying minicom, then the exp program, over the
weekend when I get a mo.
> The E2's at 9600 baud. Have you a scope that could monitor the E2's
> TXD? Lastly, was this using the same wiring as on the site for the
> EXP port, i.e. TXD on the E2 is tip.
> PC pin 2, RXD o----------o TXD o-----v | | Emailer
> 9-pin pin 3, TXD o----------o RXD o-------^ | | 3.5mm stereo
> D-type pin 5, GND o----------o GND o---------|__| jack plug
It is indeed at 9600 :) Unfortunately, no scope. Seriously
considering picking one up these days... So, yes, the wiring is the
same in terms of Tx and Rx pins. I 'confirmed' this by measuring a
voltage of 5.17V (the same as Vcc5V) on the 'tx' pin which is
consistent to a driven pin sitting at dormant '1' (as serial/RS232
usually does), and the Rx pin was at 4.5ish, consistent with probably
being a weakly pulled-up input.
> Although with JTAG it should be possible to put a little EXP-port
> downloader into RAM, run it, that pulls down a bootloader which in turn
> is happy to run the code in Smart Media card inserted in the side of
> E2 which would avoid having to flash during development.
Aye yeah; the tiniest possible loader would be good.
Another possibility (that'll be a bit more convenient than JTAGging it
each time) would be - if the /WE pin is wired on the board (which I
suspect it is) - to reprogram the PBL rom in-situ after downloading a
little JTAG loader. We could patch PBL to accept code over serial...
Or if we're going to go this route, just replace it. So many options!
;) (I'm still hoping for some sort of buff. ovf. in PBL so we can keep
it unmodified - so much safer, easier, less time consuming (in some