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I'd guess the answer varies by application? I hear, for Ata, nobody much tries to transport commands that were not standard when your host was designed. But for Atapi, I hear sampling x3F6 AlternateStatus before asserting DMACK- is the only fast, cheap, good way of discovering if you & the device agree about which way UDma data will soon be moving. (If you see BSY:DRQ = x88 you then proceed to sample the I/O C/D bits of x1F2 SectorCount aka InterruptReason.) Pat LaVarre >>> "Keith Clausen" <[EMAIL PROTECTED]> 11/28/01 03:31AM >>> ... How critical is it to access the (eg) Alternate Status Register between bursts ... Subscribe/Unsubscribe instructions can be found at www.t13.org.
