IPL_UBA already has the subtract built in:
So it shouldn't be extracted again.
The whole routine looks a little strange, but the way it works is
that an interrupt from the UBA itself sets <bit 31> in the returned vector.
Because the vector is read by code and not used by hardware, the flag
bit is "harmless."
UBA interrupts occur only under strange circumstances, like bad map
pages and device NXMs. Under the simulator, with a debugged OS, they
never happen.
For the PDP11, this includes deferring the setting of DONE on an error, allowing RSTS V4 to work correctly.
There was a minor (possibly only theoretical) bug in dt_seterr as well.
dt_seterr is supposed to stop the drive. If the drive is accelerating, at
speed, or stopped, it works fine. But if the drive is decelerating, it did
not clear out the "successor" states. In theory, the drive could be in the
middle of reversing - that is, there are successor states of accelerating
(in reverse) and at speed. So the successor states need to be cleared,
or the drive won't actually stop.
The fifth DECtape controller (the PDP8's TD8E) is much simpler and
doesn't have the problem.
- Fix protect fault for 2-word instructions so that background tasks do not
crash.
- Lay the ground work for supporting the enhanced instruction set.
- Fix disk layout bug (disks are no longer compatible with previous version).
- Add debugging support for displaying MSOS 5 system requests.
- Fix bugs found by Coverity.
The code wasn't handling interrupts correctly when TCCM was written. In
particular, if the GO bit clears DONE, the code looked for the "SET IE" case
too soon and didn't clear the interrupt that was incorrectly generated.
The new code factors "GO" into the calculation.
IPL_UBA already has the subtract built in:
So it shouldn't be extracted again.
The whole routine looks a little strange, but the way it works is
that an interrupt from the UBA itself sets <bit 31> in the returned vector.
Because the vector is read by code and not used by hardware, the flag
bit is "harmless."
UBA interrupts occur only under strange circumstances, like bad map
pages and device NXMs. Under the simulator, with a debugged OS, they
never happen.
