UDMA for Compact Flash over PC Card?

[Steven Newbury]

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

> Hi all,
> 
> I already asked about this on comp.os.linux.hardware, but didn't
> get any responses.
> 
> CF+ and Compact Flash Specification (rev 4.0) specifies Ultra DMA
> as an optional protocol for PC Card:
>    "Ultra DMA operations can take place in any of the three basic
>    interface modes: PC Card Memory mode, PC Card I/O mode, and True
>    IDE (the original mode to support UDMA)." (page 54)
> 
> Has anyone tried this? What specific CF memory cards are know to
> implement UDMA in PC Card Memory or I/O mode?
> 
> I'm looking into experimenting with improving performance of CF
> memory card when using a passive adapter under PowerBook G3.
> The PC Card is bridged with TI PCI1131. In the datasheet for
> PCI1131 I found that it "supports 16-Bit Distributed Direct Memory
> Access (DMA) on both PC Card sockets". Also signal names match
> the CF specification. I don't have access to the PC Card (obsolete)
> specification so cannot check the details there. Does anyone know
> of reasons why CF UDMA should work with this controller?
> 
> I already experimented with using PC Card Memory mode in ide_cs
> (reusing patch from Thomas Kleffel [1]) with Kingston CF/512-S
> on Linux 2.6.20. This didn't give any significant performance
> improvements. I measured that both common memory and I/O access
> time for reading data is around 1us (or longer when wait states
> are enabled). It's much more that what I would expect looking
> at the PC Card timing diagrams. Is it possible that PCI-PC Card
> bridge give such a significant latency in signal propagation?
> 
> Also when working with the patch from Thomas Kleffel I noticed
> that it probes ide devices in I/O mode!
> 
The only way of getting CF devices to run in (U)DMA mode is to physically
attach them to an IDE controller.  CF devices can electrically operate as
either PCMCIA-like or IDE devices.  If operating as a PCMCIA device it can only
be accessed with IO or MMIO.  If you want more performance than the 300ns cycle
IO access time you need to use MMIO **and set the access speed to the correct
value for that CF device**, you'll then get much higher performace (upto
20MB/s).  Using a variation on Thomas Kleffel's patch I've tried before, not
completely managed to get it working, see this lists archives.  I couldn't get
the interrupt working for some reason.


Steve


		
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