[E3-hacking] PBL & running arbitrary code

David Given e3-hacking@earth.li
Thu, 10 Mar 2005 15:04:01 +0000

On Thu, 2005-03-10 at 14:31 +0000, Matt Evans wrote:
> Last night I bodged an old USB mobile phone serial cable onto my EXP 
> port - I'm pretty sure the E3 and the E2 differ with regard to the 
> voltages on the EXP port.  That is, that webpage suggests that E3 is at 
> RS232 levels and doesn't need any line drivers.  The E2 appears to be 
> at TTL levels (0V and 5V) and as such won't work when connected 
> straight to an RS232 port.

Ung. Less good.

The core itself is powered at 3.3V, so if you're getting 5V, then it
sounds like the device does have a line converter of its own... what
does the device run off? Could this be tweakable?

> Yes this sounds sensible - if there's an Easy Enough way to get 
> bootstrap code in there via serial/EXP then we don't need any horrible 
> JTAG stuff.  Ideally something like loading our own loader through PBL 
> - our loader takes over and then we can download a DRAM image, or get 
> it to reflash the NAND in such a way that PBL will later load our own 
> code.

Another, slightly scary, alternative is to replace the PBL with our own
bootloader --- does the PBL copy itself to RAM before executing? If so
this reprogramming could be done through the PBL itself. If not, it
would have to be a JTAG thing. However, I think I'll let someone else
try this first...

Does anyone have a dump of the PBL?

David Given <dg@cowlark.com>