Network coprocessor on the F21
On Thu, 18 May 1995, Eugen Leitl wrote:
> I understood Jeff meant that once initiated, the action will
> run without requiring further attention from the processor.
> The only thing I didn't quite understand: how many links are
> there?
One input and one output.
> Can one patch through through every link to every link?
The signal has to travel through all intermediate processors, which
imposes a one-bit delay per node. This is essentially a ring topology.
The only thing I didn't get was can you run the ring in both directions,
or the direction is fixed once the processors are wired on the board.
> Did you actually integrate a crossbar switch on the die?
No, it is not needed. There is no need for arbitration at the network
level, since there is only one input and one output. The only arbitration
is done for memory access by the memory coprocessor. But then, it is not a
crossbar -- the low priority devices just wait.
> Or does each transfer virtually block the processor?
If the packet isn't for the node, it is not noticed by the memory
coprocessor. If it is, it consumes memory bandwidth. Whether the stack
processor can do actual work meanwhiles depends on the total bandwidth to
the DRAM requested by the various coprocessors, including the network one.
I hope, that I'm not confused on this point :-)
--
Penio Penev <Penev@venezia.Rockefeller.edu> 1-212-327-7423
