* Improve communication between the `hard' and `soft' interrupt handlers
to better distinguish various interrupt sources.
* Eliminate several race conditions where we would set a time out handler
only after starting the command on the hardware.
* Handle most timeouts by resetting the controller; there isn't much chance
of recovery in any other way. Currently, the exception is a timeout
on I/O, in which case we first try to pulse the controller's TC line
in order to abort the pseudo-dma sequence. Apparently, "normal"
conditions can induce such a timeout when there's no disk in the drive.
* Reduce the formatting gap parameter to 0x54.
* On the obio bus, interpret the `status' attribute.
* Minimize console diagnostic output if the errors we get appear to be
caused by the absence of a disk.
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