FEC & SDMA (bestcomm) interaction on the 5200

Grant Likely grant.likely at secretlab.ca
Sat May 16 00:52:19 EST 2009

On Fri, May 15, 2009 at 2:36 AM, Dimiter Popoff <dp at tgi-sci.com> wrote:
> Hi people,
> I am porting my (not linux) OS to the 5200. I went all the
> way understanding how the SDMA works and programming what
> I needed for it so things are now pretty stable in terms
> of disk I/O and system memory -> PCI (offscreen window
> buffers -> PCI display framebuffer).
>  And I wanted to make use of the Ethernet ("FEC", as they have
> it), hoping it would take me a few days (not my first one).
>  I am out of luck - it is practically undocumented. There is some
> talk of receive buffers which the FEC should see empty etc.,
> how on earth is that supposed to happen when it has no bus
> master capability at all? It relies on the SDMA for its bus
> activity - but in what format does it expect to get these
> buffer related data?
>  Or (more likely, at least hopefully so) this talk in the
> MPC5200BUM (and MPC5200UM, for that) is just nonsense and
> the FEC simply puts in the FIFO incoming packets, writing as
> a last .l the receive frame status word? If so, I could
> easily handle that with the SDMA.
>  Same question about transmitting. I can only hope/assume
> that the FEC will just send what it is handed through the
> FIFO by the SDMA, the very first .l being the frame control
> word, and ending when the TFD from the data drd1a or whatever
> makes it through?

It's been a long time since I've been in the bowels of the FEC driver,
but I believe you are correct.


Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.

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