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Pat, I don't recall the particulars of this case you mention, but I do remember there being a problem with a certain usb hub or device which corrupted an otherwise well-formed command from the host. That doesn't seem like a great example, but I'll play your game a bit here anyway. From what I can gather, you are unhappy because the udma burst protocol doesn't indicate precise byte counts. I'll concede that you are correct, but I don't see this as a problem because the host-side DMA hardware *should* be capable of indicating with a great degree of precision the amount of data that has transferred. This should be true of a personal computer or any protocol bridging device serving as host to the ATA/ATAPI drive. The fact that there are DMA controllers which lack this capability and systems that have chosen to use them is another argument altogether. If someone is building a bridge between different protocols, then it is their job to perform all of the translation between the different capabilities and error reporting/recovery protocols between the devices. Unfortunately, the world at large has been blessed with a variety of bridge chips that work with variable predictability. At 7:49 AM -0700 12/2/01, Pat LaVarre wrote: > >Wanna walk thru some concrete real world use cases? > >1) I remember seeing an Apple host combine with a mouse to only >occasionally zero the trailing bits of a command on its way to a Usb >disk drive. The drive saw a request to read/write zero bytes and >completed that request without error. The host only knew trouble >was at hand because the Usb1/Pio4 bridge was able to report >precisely that zero bytes had moved. > >Scsi/Atapi quite carefully accept a request to read/write zero bytes >as a complex form of no-op. I can't remembr if on paper Ata >requires an error in this case? -- --------------------- "Anything you CAN control you MUST control." Wendy Carlos --------------------- Larry Barras Apple Computer Inc. 1 Infinite Loop MS: 306-2TC Cupertino, CA 95014 (408) 974-3220 Subscribe/Unsubscribe instructions can be found at www.t13.org.
