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> A single byte, command protocol, can provide all this information and > more. With command protocol byte, your CDB is "future proof": you > don't need to specify additional bit flags for DMA, PIO Mult, TCQ, NCQ, > etc. ... > ... > In the implementation of the low-level driver, all this information is > required, and all this information is independent of transport. Yes. > For known ATA commands, this missing information can be provided by a lookup > table. Yes, spec'ing an enumeration rather than a bitmap helps us reserve, for example, x00 to mean protocol decided by opcode, rather than more explicitly specified. > For unknown (vendor reserved) commands, this information must be > specified by the client app _somewhere_, since the low-level driver > cannot know it. So how do we answer Nathan M's question - how do SATA/ PATA bridges transport vendor-specific ATA commands today? > PIO versus PIO-Mult versus ATAPI PIO > DMA versus TCQ DMA versus NCQ DMA versus ATAPI DMA Do bridges assume all vendor-specific protocol is PIO? Pat LaVarre
