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[Combining replies to Curtis's comments in two messages...]
On Thu, Jul 12, 2001 at 10:16:01AM -0700, Curtis Stevens wrote:
> This is a subject that is in the crack so to speak. If you do not address
> it in the spec, people are free to do what they want. This is why you gotta
> check the BSY bit more than once.
If the device is allowed to set BSY on it's own, checking it more than
once doesn't accomplish anything. It could just as well set BSY after
the second, third, or fiftieth check.
> If BSY=0, you can issue EXECUTE DIAGNOSTICS. This should cause a
> transition to BSY=1 within 400ns. This informs the host that something is
> attached to the cable. This means that you do not have to wait forever
> waiting for RDY=1 or timeout on some other condition.
A device could complete EXECUTE DIAGNOSTICS faster than you could poll the
status after issuing the command, and you'd never see BSY set. So using
BSY that way for device detection isn't reliable. And as I've said in
another post ATAPI devices don't set DRDY after reset, or after EXECUTE
DIAGNOSTICS, so waiting for RDY=1 isn't enough either.
jcastle
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