Re: [openwince-list] Adding support for MPC82xx

[Marcel T. <ma...@te...>]

On Wed, Jul 20, 2005 at 03:22:33PM -0700, Jeff Carr wrote:
> On 07/20/05 11:20, Marcel Telka wrote:
> > On Tue, Jul 19, 2005 at 07:27:08AM -0700, kacham ashok wrote:
> > 
> >> I want to add the support for mpc8241 to jtag tools(
> >>jtag-0.5.1). I have got BSDL file for mpc8241. what
> >>are the steps needed for it.
> > 
> > 
> > Please read mailing list archives. The steps were described there.
> > 
> 
> What are the limits to what can be done with the PPC chips via the jtag
> interface.

JTAG Tools currently supports only boundary scan.

> 
> The powerpc chips are usually programmed with the BDM port. Can anything
> really be done via the JTAG port?

Yes. I've programmed flash chip attached to the CPU using JTAG Tools.

> Has anyone been able to program
> registers or setup SDRAM/SRAM or anything like that?

This is not possible using boundary scan.

> 
> I'd like to try to do it; if I knew it was theoretically possible. If

I'm not sure. But if yes, then you need to write new bus driver for that job.

> one was able to sucessfully program the chip select registers on the
> 82xx processor, then you might be able to write firmware into ram and
> execute it.
> 
> Then again, this seems more like some sort of unrealistic dream.
> 
> For instance, I wonder about what these commands would do on a ppc cpu:
> peek          read a single word
> poke          write a single word

They read/write to the external chip (e.g. flash) using boundary scan. It is
implemented in particular bus driver.

> 
> Would that really write values into the memory space of the ppc cpu?

With current bus driver no.

> 
> If so, and you could actually identify the 82xx chip, you could dump out
> the cpu internal registers (probably at 0xFFF00000 or something like
> that -- read the 82xx manuals). That would be real progress!

With current bus driver no. You need different bus driver.

> 
> Then, if you were actually able to write a value into the cpu register
> space you would be getting somewhere -- you might even be able to setup
> the external chips on the cpu.

If you want to drive external chips, you don't need to write to the internal
registers. Boundary scan is sufficient for slow chips, like flash. For chips,
which requires quick access, the boundary scan is too slow.


Regards.

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