Re: FFs for GNT and REQ

["Weng Tianxiang" <wtx@umem.com>]

Hi,
I dont' agree with Spaeth opinion.

When your REQ# is asserted and once Bus Arbitor gives you GNT#, it will not
disappear for at least 5 clocks or FRAME# is asserted, whichever comes
first.

My reason is not from PCI specs, but from my reasoning: 5 clocks are needed
to guarantee that some PCI masters behind bridge get the correct GNT#
response from arbitor. That FRAME# is asserted means PCI Bus client has got
the bus access. My guess is as much as 16 clocks may be generated by PCI
bridge to wait for FRAME# assertion before arbitor deassert GNT#.

Weng Tianxiang
Micro Memory Inc.
9540 Vassar Av.
Chatsworth, CA 91311
Phone: 818-998-0070, Fax: 818998-4459


----- Original Message -----
From: Stefan Spaeth, tel. +49 711.821.43051, fax 45571 <S.Spaeth@alcatel.de>
To: <pci-sig@znyx.com>
Cc: Zipper Thomas <Thomas.Zipper@icn.siemens.de>
Sent: Friday, September 08, 2000 9:24 AM
Subject: Re: FFs for GNT and REQ


> Zipper Thomas wrote:
> >
> > Hi,
> >
> > would I violate the PCI Spec when I add flip-flops to GNT and REQ lines
of an arbiter?
> > (in other words the arbiter sees the REQ signal delayed by one clock and
the master requesting the bus sees the GNT signal also delayed by one clock)
>
> I don't see a problem for REQ# (although it may not be nice to
> assert request and then not take the bus). Anyway, I assume that an
> arbiter would be able to cope with that situation (potentially arising
> at the end of a transfer).
>
> It is, however, certainly critical for GNT#. You may only assert FRAME#
when
> GNT# is
> detected asserted - and this may no longer be the case one cycle later.
> Therefore I don't think your idea works for GNT#.
>
> Regards,
>   Stefan
>
> > Thnx & Ciao
> >
> > Thomas
>
> --
>       _/        ALCATEL AG           Stefan Spaeth
>      _/_/       Stuttgart            ASIC Design
>     _/  _/
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>
>