** This is the quasi-official and semi-temporary T13 email list server. ** > >In AtapiUdma, by spec, when host and device disagree over direction, > > This statement and the discussion that follows it completely > baffles me. > Why is there ever a disagreement > of the direction of a command's data transfer? Because two different people independently wrote the host software and the device firmware and by design the encoding of the interface permits disagreement. Usb core, by contrast, encodes data direction, max data length, opcode and parameters separately. I have NEVER seen host and device disagree at the Usb core level. I imagine this because it would be obvious on a bus trace who was at fault. > For ATA commands each command code that can transfer > data has a specified standard data transfer direction. Ata is unusual among mass storage protocols in how intensely it confuses all the levels of the driver. Maybe that's best: if nothing but a monolithic driver works, then none of the complex situations arise in practice? Aye, specified. Not obvious. If I'm looking at a bus trace, I have to go pick the correct version of some separate book before I can argue the host and the device should be in agreement. Let's take the example of the vendor-specific Ata ops. When I see a vendor-specific op cross the bus, how can I know whether to expect in or out, how many bytes, PIO or DMA, what flavour of DMA .... > For SCSI commands sent via the ATAPI PACKET command > each SCSI command code that can transfer data > has a specified standard data transfer direction. There is a tremendous amount of confusion of most anything other than block read/write. > The discussion (that I did not include here) > points to only one thing: bad host design Aye. People let legacy Dos apps decide a cb, the data direction, and the data amount. How correct that is for the device that happens to be connected is not well specified. -- If you have any questions or wish to unsubscribe send a message to Hale Landis, [EMAIL PROTECTED] To post to this list server send your message to [EMAIL PROTECTED] For questions concerning Thistle Grove Industries or TGI's list services please send email to [EMAIL PROTECTED]
