FEC & SDMA (bestcomm) interaction on the 5200

[Dimiter Popoff]

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?

 If the above assumptions are correct, I could manage it
in a reasonably short time. 
 I know this is an "untypicall" question, but people who
have wrestled the FEC & SDMA may have enough observations
to confirm or reject my assumptions and perhaps provide
some more insight.

Thanks for any input,

Dimiter

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Dimiter Popoff               Transgalactic Instruments

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