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I would love to have an equivalent SG-list to DMA for PIO, then you could share the same table and be done. Additionally it would allow for high memory access for PIO calls, sigh, it was but a dream ... Cheers, Andre Hedrick LAD Storage Consulting Group On Wed, 10 Apr 2002, Hale Landis wrote: > This message is from the T13 list server. > > > On Wed, 10 Apr 2002 14:00:23 -0700, Ooi, Thien Ern wrote: > >This message is from the T13 list server. > >Yes, the ATA interface is indeed returned to the "PIO State" whenever the > >device registers are accessed. Because the (intel) host adapter does not > >make any assumption on what the status or any other register should be > >during a UDMA burst, it always runs the "PIO" cycle to the device. > > But why do this? From day one of this interface we know that during > the execution of a DMA data transfer command a device should have > status of BSY=1 (yes, some devices have status of BSY=0 DRQ=1 but > that doesn't matter, either status tells the host the device is > busy). So why should a host adapter terminate a DMA data burst in > progress when the host does a read of one of the device registers? > Why not just tell return fake data of 80H and let the DMA data burst > continue uninterrupted? > > To me this is just all part of the sad state of current ATA host > adapter designs. Except for a few efforts ourside of the main stream, > no real attention has been paid to how ATA host adapters can be > improved. Worse yet, little attention has been paid to how > inefficient today's stupid host adapters are. Another question: Can > you give me one good reason why (5 years ago!) the host side should > not be able to use a PRD list for PIO data transfers and have the > host adapter preform the equivalent of the x86 REP INSx/OUTSx > instructions? Given the popularity of ATA/ATAPI and all the > improvements done in device designs there is no excuse for the host > adapter side of the interface to be in such a sad state! > > (Oh yea, I know I will hear all the same old excuses... Well ATA is > obsolete... Soon to be replaced by <you name it>... Microsoft won't > support the change... It would cost too much... blah blah blah... We > can't spend money on this but gee wiz we have the money to design > 1394 interfaces, USB interfaces, <you name it> interfaces, but no > money for ATA... only the most popular storage device interface on > this planet.) > > > > *** Hale Landis *** www.ata-atapi.com *** > > >
