[E3-hacking] PBL & running arbitrary code

Matt Evans e3-hacking@earth.li
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 
> out
> 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 
> E3's
> 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 
> the
> 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