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> > UDma ... If M more clocks arrive, > > then a sender that guesses the receiver > > willingly requested D = N * 2 bytes > > can be wrong by anywhere from 0 to M * 2 + 1 bytes. > I'm not saying that changing protocols > could not improve them. But it takes > two years to get those changes to market, Yes but. Teaching an Atapi device to report accurate residue (the count of bytes clocked that were not willingly requested) is fast & good & cheap, as protocol changes go. Changing to report accurate residue comes a lot easier, for example, than to learn to support 48 rather than 28 bit Lba's in Ata. I'm thinking people who control both bridge and device can turn this quickly, to fix the first plug 'n play horror that goes away with this fix. I'm now hoping to see this change roll in across our product line as a metal-mask firmware change only, no real silicon change. I'll have to go reread the relevant portions of the Atapi standard more carefully, but I'm thinking I remember that standard leaves us lots of room in the task file of the final INTRQ of a command to change an Atapi device to accurately report residue at will. > and you will always have to contend > with older designs without the "fix." Aye. I can get competitive plug 'n play time-to-market edge and some price break if just one if my partners makes for me a bridge fully transparent merely across my own product line. But I can ask for a better break if my chosen partner can find a lot of other customers to share the cost. I'm not at all clear on what the least wrong heuristic is for guessing what residue is. I imagine the final choice of a heuristic might end up a tightly guarded trade s*cret that gives people competitive edge. That is, this heuristic will become a "secret sauce", like how creatively boot Bios interpret our quasi-public Ansi Ide standards. Secret sauce gets purchased expensively by paying people to isolate the root evil in a series of plug 'n play troubles over time. If so, then standardising a way for Atapi devices to report accurate residue will be the only low-cost-of-entry route for latecomers to enter the market. Pat LaVarre Subscribe/Unsubscribe instructions can be found at www.t13.org.
