On 02/09/07, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote: > > In my research on this issue, I do remember coming across an > > announcement you made not so long ago regarding the libata.pata_dma > > command - however because of my revelations with Windows detailed at > > the end of my reply to tejun, I am curious as to whether MWDMA is > > really DMA at all? I also believe it runs at about the same speed as > > the top PIO speeds too? > > MWDMA is DMA but MWDMA2 and PIO4 use the same data transfer rates - the > DMA modes make it easier to offload the processing. In fact MWDMA isn't > really needed - the Cyrix CS5520 and some other chipsets can do DMA in > the chipset up to MWDMA while talking PIO4 to the device. > > But to answer the question - there is a real difference electrically > between MWDMA2 and PIO4 > > > I also know that my SATA-PATA arrangement is hardly ideal - but the > > controller, using the original HDD, supports udma5 - so I am wondering > > why it does not detect, and use, that with the CF card - this brings > > me back to the question I originally posed and tejun answered - is > > there any way to force it to use UDMA4 - because I know it is > > supported by the card? > > If it is offered by the card it should be automatically selected. Can you > mail me the hdparm identify data for the drive ? > > > > Also, the CF-IDE bridge is a cheap one (not that there were much > > choices) from ebay - and the documentation that comes with it states > > that it supports DMA - in which case is there any way I can verify > > that? What are the prerequisites for DMA support? (Do certain pins > > need to be connected, for example?) > > For DMA certain pins must be connected correctly. For UDMA the entire > cable assembly including adapter must also meet very strict capacitance > and other loading requirements - few do, especially hung off the end of > cables. > > Hello Alan, I sent a reply to the list with the data that tejun asked for before I replied to you - I guess you haven't got it (yet?). I'll forward it to you once I finish this e-mail. The CF-IDE adaptor is plugged straight into the header - and as far as I can tell it doesn't do anything fancy (e.g. there are no ICs on there) - but simply maps the pins from the CF slot to the IDE connector. As such, its effect should be minimal... Eddie - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
