Re: cache memory

["Richard Walter" <rwalter@auspex.com>]

> Hi,
> 
> I had a PCI ATM card that has the SBO and SDONE signals
> pulled up high.   Does this mean that the memory on the
> PCI will not be cached by the PC cache?   I want to know 
> whether when I read memory locations on the PCI card, 
> would I be actually reading the real memory content or 
> may be some ghost in the PC cache.

Most PCI systems do not cache PCI memory space.  If it did, then the
host CPU would have to be snopped for every PCI transaction, which
would kill bandwidth, or the host bridge would have to remember the
state for every cache line in PCI space, which would require a fair
amount of logic.

However, it should be the motherboard, not the card which pulls
up the SBO & SDONE signals.  See section 2.2.7 (page 14-15) of the
PCI 2.1 spec for info of this.

> 
> Any information is very much appreciated.
> 
> -------------------------------------------------------------
> Au Kum Chuen <au@sol.fujikura.co.jp  or aukc@pacific.net.sg>
> 
> 

-Richard Walter
rwalter@auspex.com
Note: I speak for myself, not for Auspex.


ÓL9