All-ones problem with FCC1 on MPC8541

Mark Chambers markc at
Fri Oct 29 04:02:46 EST 2004

> I checked port configuration and clock routing registers in
> cpm2_io/fcc_enet.c again and again, but all I get in and out is ones.
> 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
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.

Mark Chambers

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