FEC & SDMA (bestcomm) interaction on the 5200

[Dimiter Popoff]

> From: Grant Likely <grant.likely at secretlab.ca>
> Date: Fri, 15 May 2009 08:52:19 -0600
> Subject: Re: FEC & SDMA (bestcomm) interaction on the 5200
> To: Dimiter Popoff <dp at tgi-sci.com>
> Cc: linuxppc-dev at ozlabs.org
> 
> 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).
> >
> > =A0And 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).
> >
> > =A0I 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?
> > =A0Or (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.
> > =A0Same 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.
> 
> g.
> 
> -- =
> 
> Grant Likely, B.Sc., P.Eng.
> Secret Lab Technologies Ltd.
>

Thanks for the input, Grant. It matches the memories of a guy
at Frrecale who has had to deal with it ass well, so I guess
I am on the right path - It won't be without trying this or
that out but I am well enough positioned to start.

Dimiter

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