This message is from the T13 list server.
On Mon, 11 Feb 2002 08:56:59 -0700, Pat LaVarre wrote: >This message is from the T13 list server. >Seeing that C/D I/O = x03 StatusIn or x01 reset signature is the >only way a host can distinguish a separately powered reset from a >normal end-of-command. Whoa! This makes no sense. What if the last command to the ATAPI device was not a PACKET command? What if it was an invalid ATA command? There is no IO or CD bits at the end of these commands and it is unlikely that this 03H bit pattern would be in the Sector Count register. AND... If an ATAPI device is "reset" it should have a SK=6 ASC=2x Unit Attention error to report. Are unexpected/unplanned "resets" really that much of a problem? I have never heard an ATA hard disk vendors say this is a problem. If it was I am sure we would define a method for an ATA hard disk to report the equivalent of SCSI SK=6 ASC=2x! Your suggestion that a host should use the IO and CD bits to detect a "reset" is a totally inappropriate use and perhaps even an invalid use of the bits of the Sector Count register. >Seeing that C/D I/O = x02 DataIn or x00 DataOut is the only way a >host can discover which way the device wants to move data for a >command not standardised before both the host and the device >shipped. I do not know of any host that can function properly if it does not know the direction of data transfer for a command BEFORE the command is issued to the device. If a host doesn't know the command is a "write" then where will it find the data the device will request. This use of IO and CD really makes no sense at all. >Seeing that C/D I/O = x01 CommandOut is the only way a host can >distinguish between a DRQ expected to move command out from a DRQ >expected to move command out. Clearly incorrect. The first time an ATAPI device has status of BSY=0 and DRQ=1 it is requesting the "command packet". The host NEVER needs to look at IO and CD to determine this state. *** Hale Landis *** www.ata-atapi.com *** Subscribe/Unsubscribe instructions can be found at www.t13.org.
