All-ones problem with FCC1 on MPC8541

Stefan Nickl Stefan.Nickl at
Fri Oct 29 22:50:03 EST 2004

On Thu, 2004-10-28 at 14:02 -0400, Mark Chambers wrote:
> > The packet sizes I receive look reasonable, but the buffers are
> > filled only with 0xff. The same goes for sending, the contents
> > of the buffers are OK (dhcp discover...), but when capturing
> > the output on the other side with ethereal, the packet is again
> > all 0xff.
> >
> > We just discovered that apparently preamble, frame delimiter and FCS go
> > out over the MII (at least TxD[0:3] change state), so I don't suspect a
> > hardware bug.
> >
> I would guess the problem is at the DMA level, that the FCC is
> reading/writing
> ffs to/from memory for some reason.  The preamble and FCS come from the
> FCC itself, not memory, so that's why you see them.  I'd guess some kind
> of mismatch with the kind of cycles generated by the FCC DMA and the
> memory controllers.

I've tried loopback mode today, and it's the same story:
only 0xff on the receiving end.
We looked hard at the manuals for anything that could cause the
kind of DMA problems you describe, but yet to no avail.
The chapter about SDMA seems to mainly describe some error status
registers, and they remain at their default value when running the FCC.

We'll try to get hold of CDS eval board schematics to check more on the
hardware side, in the meantime, do you have an idea of which registers
to look at in particular?

Stefan Nickl
Kontron Modular Computers

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