RE: Intel chipsets and prefetch during PCI target read

[Lame Brooks-G14738 <brooks.lame@motorola.com>]

	I asked an Intel SIG guy a while back and they said none of the
current Intel north bridges could do prefetching and he didn't know of any
plans to change that.  Of course, we also talked about why - how does the
bridge know what ranges are prefetchable?  Well, at fist thought, it still
seems to me that this could be solved with an extra couple config registers
to tell the bridge what range is prefetchable.  
	But for now, if you want to get data to host memory fast, in an
Intel machine, you need to push it with a mastering peripheral.  
-- BrooksL

> -----Original Message-----
> From: William F Hong [mailto:wfhong@west.raytheon.com]
> Sent: Wednesday, 23 August, 2000 11:53
> To: pci-sig@znyx.com
> Subject: Intel chipsets and prefetch during PCI target read
> 
> 
> Hello,
> 
> The system we are developing contains a homegrown, target 
> only, PCI ADC
> card which uses a PLX Technologies 9050 PCI interface chip.  Our
> application requires that the contents of the ADC sample 
> memories be read
> rapidly to system memory.  Using a bus analyzer I have 
> observed that our Intel
> 440BX Host/PCI bridge generates a single PCI Memory Read transaction
> for each 32-bit Dword that the Pentium requests even though 
> the reads are
> to consecutive ADC memory locations.  Isn't the 440BX capable 
> of doing any
> prefetching, i.e. generating a PCI burst read in 
> anticipation?  I know that our
> PCI target can support burst reads because I have used the 
> bus analyzer as
> a master and performed the same transfer.  After reading
> related posts in the PCI Reflector Archive I find two 
> different answers.
> Some say that north bridges can do prefeching from capable 
> PCI targets (target
> contains prefechable and cacheable memory) others say that 
> north bridges are
> incapable of generating burst reads from PCI.  An Intel 
> Customer Support person
> on the Intel Chipset Forum indicates that none of their 
> chipsets have this
> capability.  I would like to resolve these contradictions 
> before I tell our hardware
> designers that we can only achieve the desired PCI to Host 
> throughtput by
> redesigning their boards with PCI master capability.  So 
> assuming that the ADC
> cannot be redesigned...
> 
> 1)  Can the time between reads by the processor affect the 
> Intel 440BX's ability
>       to do a prefetch, i.e. is my Windows NT driver too slow?
> 2)  If the Intel 440BX chipset cannot prefetch PCI data are 
> there any other bridges
>      (Intel or other) for Pentium systems which can?
> 3)  Does anyone know of another mechanism to transfer data 
> from a PCI target to
>      system memory which takes advantage of PCI burst cycles?
> 4)  I understand that target memory prefechable is set in the 
> base address register
>      of the PCI target's configuration space only  if the 
> target memory prefech has no
>      side effects.  But what does it mean in this context to 
> be cacheable?
> 
> Thanks in advance.
> William Hong
> Software Engineering
> Raytheon Missile Systems
>