Re: target burst accesses - resending

[Frank Story <frank.story@acoustictech.com>]

Hi Vijay,

Just another quick note on disconnects. It would be preferable to disconnect
only if the access is a burst. If a disconnect always occurs, then non-burst
cycles are un-necessarily disconnected, which forces the bus master to release
the bus and re-arbitrate. I've seen this cause significant performance
degradation in some old ISA bridges.

Frank


Monish Shah wrote:

> Hello Vijay,
>
> I see something contradictory here.  You are designing a 64 bit card but
> you don't want to support burst accesses.  As Duane Clark's reply noted, it
> is OK to not support burst accesses as long as you don't have too many
> accesses.  (I.e., performance requirements are not high.)
>
> But, if performance requirements are not high, why is the card 64 bit?
> This is the contradiction.
>
> Anyway, technically you are free to not support bursts as explained by
> Duane, even on a 64 bit card.
>
> Monish
>
> ----- Original Message -----
> From: Vijay Chougule <vchougule@altavista.com>
> To: <pci-sig@znyx.com>
> Sent: Tuesday, August 15, 2000 4:45 AM
> Subject: target burst accesses - resending
>
> > Hi,
> >
> > I am designing a 64-bit PCI target card. The card's internal register
> space and the data space are memory mapped. The only agent that does target
> accesses to the card is the host processor. I am trying not to support
> burst target read or write accesses to the card from the host processor.
> Since the card is memory mapped, I do not know whether there can be burst
> accesses to the card even if the software always accesses one word (32 bit
> at a time). In other words does the MIOC on the host system, convert the
> single word accesses (to consecutive locations) into burst accesses for any
> reasons ?
> >
> > Is it a good idea to support only single word target accesses ? Would I
> need to do target disconnect after each word or the host processor will end
> the transaction after the first word ?
> >
> > Thank you in advance,
> >
> > Vijay
> >
> > P.S. Sorry for the wrong subject earlier.
> >
> >
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--
Frank Story
Acoustic Technologies, Inc.                   Ph. (480) 456-3641
1921 S. Alma School Road, Suite 313           Fax (480) 456-0105
Mesa, AZ 85210                      frank.story@acoustictech.com