RE: How to make Burst on PCI bus?

["McDonald, Ed" <mcd@xgate.columbiasc.ncr.com>]

Most host-PCI bridges will "gather" consecutive writes and create a
longer stream
of write accesses to the downstream PCI bus.

This is generally not true for reads of PCI.

However, even with this behavior it is still possible that burst writes
from a CPU
may be broken up into smaller bursted streams depending several factors
such as the source data's location, the host-PCI bridge design, and
other interference on the CPU's bus.  For example, if the source of the
data being moved
is not in the CPU cache but instead in memory, then the CPU will
have to pause writing on each cache line boundary while it reads from
the source
address (from memory).  Depending on how slow the return of data from
memory and the timing of the host-PCI bridge this may require a 
break in the PCI stream (again depending on the host-PCI bridge
timings and design).  Similarly, if other host-PCI bridges can 
arbitrate and own the host bus (e.g. DMA in progress) this will
break up the CPU writes to PCI.

Ed McDonald
NCR

>----------
>From: 	ckim@winky.etri.re.kr[SMTP:ckim@winky.etri.re.kr]
>Sent: 	Wednesday, June 04, 1997 8:33 AM
>To: 	Mailing List Recipients
>Subject: 	How to make Burst on PCI bus?
>
>Hi! Everyone.
>
>I'm a newcomer on this mailing list.(I'm happy to be here)
>Here goes the basic, very easy question.
>In my understanding, for host-PCI bridge, the bursting is done automatically 
>by hardware like host bridges. So the software programmer doesn't care about
>from what words to what words will be written or read in burst.
>I saw in LSI logic's PCI core manual that the PCI core monitors the address 
>sequence and when the address is in increasing order, it converts the writing
>actions into a single burst. 
> Is my understanding right? (so called "combining actions")
>Or is there any burst-making machine instruction in CPUs like Pentium?
>Can we control the bursting of data  transfer explicitly in the application
>S/W level?
>Someone, Please answer to my question. Any comments are welcome.
>
>Chan Kim
>ETRI
>
>
§¸¦