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  #1 (permalink)  
Old 04-11-2006, 08:50 PM
Ricardo
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Default PCI speed.

Hi.

I have a PCI board developed and I have little acess to the FPGA PCI
core, since it was not developed in house. I can say it makes no burst
accesses. My proble is that I used to have a reasonable speed with these
boards with athlon/semprom boards, regardless of chipset. After the
chipsets/processors changed to socket 754 and 939 (and got
HyperTransport, but I don't know whether it's related) i got a 20% speed
drop, a little too much. With the nForce4 chipset I may get to the same
speed as before, but I can't achieve it with a stable bandwidth. I don't
have any intel boxex around to test with it.
Does anyone has any clue on what's going on (even better, a solution)?

Thanks,
Ricardo
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  #2 (permalink)  
Old 04-11-2006, 09:03 PM
John_H
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Default Re: PCI speed.

Do you have a PCI Analyzer? If you're a PCI target, I wonder if you're
getting an abort and a retry on occasion for data that your design doesn't
supply fast enough. I thought the abort period was somewhat programmable in
some PCI bridges.

"Ricardo" <[email protected]> wrote in message
news:[email protected]
> Hi.
>
> I have a PCI board developed and I have little acess to the FPGA PCI core,
> since it was not developed in house. I can say it makes no burst accesses.
> My proble is that I used to have a reasonable speed with these boards with
> athlon/semprom boards, regardless of chipset. After the
> chipsets/processors changed to socket 754 and 939 (and got HyperTransport,
> but I don't know whether it's related) i got a 20% speed drop, a little
> too much. With the nForce4 chipset I may get to the same speed as before,
> but I can't achieve it with a stable bandwidth. I don't have any intel
> boxex around to test with it.
> Does anyone has any clue on what's going on (even better, a solution)?
>
> Thanks,
> Ricardo



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  #3 (permalink)  
Old 04-11-2006, 11:47 PM
Weng Tianxiang
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Posts: n/a
Default Re: PCI speed.

John_H,
I disagree your opinion.

PCI traffic and performance heavily depends on chipset system. We
observed that board with same PCI designs may have dramatic speed
changes on different chipsets. Chipsets from some manufactures have a
better performance, some have bad performance. Usually the latest
version of chipsets will have a better performance over older versions
for the same manufacture.

It is first time to hear that in a new chipset system, there is a 20%
speed decrease. It means to me that most likely the new chipset has a
different schedules than before that may put PCI transactions 1 level
of order of delay. For example, for older version of chipset, the
schedule algorithm in the chipset selects next request to go based on
their arrival time from a incoming queue; for newer version of chipset,
the schedule algorithm in the chipset may change to response PCI
request after 4 CPU requests are answered. If so, it would appear and
report that CPU gets faster performance while sacrificing PCI
environment that nobody pays attention to.

I don't know why 20% speed reduction really is. That must be confirmed
by PCI bus analyzer. But the reason John_H indicated is the least
likely real reason.

You can imagine with faster DDR/DDR II system, possible two channels of
them and much higher working frequency, a 20% performance decrease
cannot be blamed on the board side.

Weng

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  #4 (permalink)  
Old 04-12-2006, 09:25 AM
Kolja Sulimma
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Default Re: PCI speed.

Ricardo schrieb:
> Hi.
>
> I have a PCI board developed and I have little acess to the FPGA PCI
> core, since it was not developed in house. I can say it makes no burst
> accesses.

Is your board handling the transactions as initiator or target?
If it is a target, the burst length is controlled by the CPU.
AFAIK the best you can do with IA32 is a burst of length four by using
SSE 128 bit moves.

If your board is the initiator, it controls the burst length, but the
chipset could abort or retry transaction to enforce shorter burst. But
I doubt that it will do that below a length of four.

Use chipscope to have a look at what happens on the bus.

Kolja Sulimma
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  #5 (permalink)  
Old 04-12-2006, 09:28 AM
Nial Stewart
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Default Re: PCI speed.

"Ricardo" <[email protected]> wrote in message news:[email protected]
> Hi.
> I have a PCI board developed and I have little acess to the FPGA PCI core, since it was not
> developed in house. I can say it makes no burst accesses. My proble is that I used to have a
> reasonable speed with these boards with athlon/semprom boards, regardless of chipset. After the
> chipsets/processors changed to socket 754 and 939 (and got HyperTransport, but I don't know
> whether it's related) i got a 20% speed drop, a little too much. With the nForce4 chipset I may
> get to the same speed as before, but I can't achieve it with a stable bandwidth. I don't have any
> intel boxex around to test with it.
> Does anyone has any clue on what's going on (even better, a solution)?



Have you played about with the BIOSs of the two systems to see how the
PCI inerfaces are configured? This might be worth looking at, from memory
there are a few PCI parameters that you can play about with here and this
might improve your performance somewhat.


Nial.


----------------------------------------------------------
Nial Stewart Developments Ltd Tel: +44 131 561 6291
42/2 Hardengreen Business Park Fax: +44 131 561 6327
Dalkeith, Midlothian
EH22 3NU
www.nialstewartdevelopments.co.uk



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  #6 (permalink)  
Old 04-13-2006, 12:44 PM
Ricardo
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Posts: n/a
Default Re: PCI speed.

Hi.

I fanally could test with an intel box and it works the same.
As I don't have a PCI-analyzer, I'm thinking in the possibily of making
some tests with a logic analyzer. That's not that much urgent, since I'm
changing the system to USB, and I'll need to shorten the desing time due
to this PCI problem. Anyqay, I'd need to try to solve this to assure
maintance of the machines that are in field.
Thanks a lot for the help.

Ricardo

Ricardo escreveu:
> Hi.
>
> I have a PCI board developed and I have little acess to the FPGA PCI
> core, since it was not developed in house. I can say it makes no burst
> accesses. My proble is that I used to have a reasonable speed with these
> boards with athlon/semprom boards, regardless of chipset. After the
> chipsets/processors changed to socket 754 and 939 (and got
> HyperTransport, but I don't know whether it's related) i got a 20% speed
> drop, a little too much. With the nForce4 chipset I may get to the same
> speed as before, but I can't achieve it with a stable bandwidth. I don't
> have any intel boxex around to test with it.
> Does anyone has any clue on what's going on (even better, a solution)?
>
> Thanks,
> Ricardo

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  #7 (permalink)  
Old 04-13-2006, 04:18 PM
Brannon
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Posts: n/a
Default Re: PCI speed.

The biggest issues I've had with this is board capability detection. I
have some boards that are supposed to run PCI64 @ 66MHz. However, in
some motherboards they are detected as 32bit wide at 66MHz or 64 bit
wide at 33MHz. In both those cases I lose 20-30% of the speed. There
should be a way to determine which mode your board is running in, or if
all else fails scope the clock pin and REQ64/RST signals at boot.

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