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Hi, As you all know, there is support for queued commands in ata4 and later. Some IBM (Deskstar) and Western Digital (Expert) drives implement this (I know of no others). It works, and for a single drive on a channel, it works fairly well. However, there are some things missing that would be nice to have. One of these features is ordered tag support. Unfortunately there are no option bits left for the tags in the standard taskfile, and to enable this to work on both 48-bit lba and older, I had the following idea: Use the NOP command with features register used for options. There's already (sort of) precedence for doing something to this effect, with the nop auto poll suggestions. COMMAND = NOP (0x00) FEATURES = 0x01 Enable Auto poll COMMAND = NOP (0x00) FEATURES = 0x02 Tag barrier So it would be possible to issue, eg, 12 commands, issue a NOP with features 0x02, and then start command X. X would then be guarenteed not to be started before the previous 12 commands had finished. Comments? The above is just a quick write-up, I can make this is general suggestion if need be. -- Jens Axboe
