it appears that for pio reads and writes, sdata.c (the plan 9 ata driver)
omits waiting for Drdy. normally drives assert Drdy very quickly, but its
in the spec and i've tripped on a few slow parts that are not ready when
we send them data:

Sep 8 13:00:49 EDT 2008 sdata.c 54744 [quanstro]
sdata.c:1421 c /n/dump/2008/0909/sys/src/9/pc/sdata.c:1421
< if(ataready(cmdport, ctlport, drive->dev, Bsy|Drq, Drdy, 101*1000) < 0)
---
> if(ataready(cmdport, ctlport, drive->dev, Bsy|Drq, 0, 101*1000) < 0)


i'm pretty sure that the same test needs to be in atapktio as well.
(could this be the disagreement with vmware?)

it is interesting that it's been that way for a long time.

- erik