UDMA for Compact Flash over PC Card?

[Steven Newbury]

--- Piotras <piotras at gmail.com> wrote:

> Hi Steve,
> 
> Thanks for your replay.
> 
> My device supports 250ns cycle (according to CIS). I set it up
> for MMIO (PCMCIA) using the Thomas Kleffel's patch and verified
> the settings of the window registers in PCMCIA bridge. The
> measured throughput for reading from the CF does not exceed 2MB/s.
> 
> I verified the actual time for MMIO reads from data register
> by the CPU. The average time for reading 16-bits word is about
> 1us (it's consistent with the throughput). When I was changing
> the cycle timing, the measured time for reads changed accordingly
> (~750ns + cycle time). I cannot verify what causes this ~750ns
> delay. Maybe it's the propagation delay introduced by the two
> bridges (CPU-PCI and PCI-PCMCIA). If it would be the case, the
> DMA by PCMCIA bridge could give significant improvement.
> 
> After I send the previous email I realized that the PCMCIA bridge
> datasheet is older then ATA specification that introduced UDMA.
> I think that the DMA supported by the PCMCIA bridge is something
> similar to single-word/multi-word DMA. The Compact Flash
> Specification does not specify any of these for PCMCIA. Still some
> vendors could possibly implement it...

I actually have burst DMA working on the PXA PCMCIA interface.  I've actually
had transfers of >8MiB/s with a CF card although I was overclocking IO, rather
than using MMIO due to my inability to get it to deliver interrupts as I
mentioned previously...  I really need to have another look at that! 
> 


Steve


	
	
		
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