On Fri, 7 Oct 2005 08:45:14 -0400
Timothy Miller <[EMAIL PROTECTED]> wrote:
> > How about using here 64bit for both address and data ?
> > Or 64bit data and 48bit address (though i doubt that these 16bit
> > would make much difference) ?
>
> Why do we need that? Is there something special about PCI Express?
> Ok, I see your point on the address, but keep in mind that OGA's
> internal address space really only needs 28 bits, and if we have a
> PCIe controller that can do 64-bit addressing, it's going to translate
> down.
Yes, i realized too after i send the mail.
> The only reason for 64-bit data is speed. If we had a 64-bit
> PCI interface, it might help, but even then, we could just double the
> data rate on the local bus.
How much up can the data clock go? I mean a single lane of
PCI-E IIRC gives 2.5Gbit/s, which is about 80MWords/s at 32bit word size.
This would mean that we would need 80MHz per PCI-E channel.
> > If we have excess pins, how about using them to feed two
> > "banks" of DRAM that can be independently accessed?
> > I can imagine that this would give some performance,
> > though i can not put it into numbers.
>
> Actually, there are four memory controllers. Memory is arranged in
> stripes of pixel pairs interleaved with adjacent pairs over adjacent
> memory controllers.
Ok
> > What about JTAG ?
>
> Yeah, that's part of what I was missing above with the control
> interface. Oh, and we need to not forget some headers to reprogram
> the Lattice.
Maybe it would be a good idea to have some pins to be used
to represent some internal states for debugging.
Apropos, have you thought about a way to clock the whole card slower
so that it could be debugged with a cheap digital analyser?
Attila Kinali
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