The output-status function applies only to character devices, and in block-device drivers it should do nothing except set the done flag. This function returns the current output status for the device.
The output-status function is called with
RH + 2 BYTE Command code = 10 (0AH)
It returns
RH + 3 WORD Status:
If busy bit = 1, write request waits
for completion of current request.
If busy bit = 0, device idle and
write request starts immediately.