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.
As discussed in #378
The fixes include:
1. Tightening up the "magic" code so that it can now tell EXE, SAV, and RIM
formats apart.
2. Skipping the loader itself for both RIM10B and ITS RIM. (PDP10 Macro manual
says that RIM10B always includes the loader.) 3. Distinguishing ITS RIM from
RIM10B by the length of the loader block.
4. Adding the slight differences in processing between ITS RIM and RIM10B.
There is no documentation change. -R or the extension .RIM still invoke the
RIM loader, and the code tells ITS and RIM10B apart.
As reported by Josh Dersch in #358
Read hardware notes:
- While the TCCM error bit is a real flop, it is supposed to reflect
the OR of the TCST error bits at all time, so it is updated on read.
- A read of TCDT while the function is RALL clears DONE.
Write hardware notes:
- The TC11 behaves much more like a traditional DECtape controller
than a typical PDP11 peripheral. In particular, execution is
initiated/controlled by any write to TCCM, rather than setting
the GO (DO) bit. Unless the function is STOP or STOP ALL, writing
TCCM will put the selected tape in motion.
- Writing GO (DO) clears DONE (READY) and the error flops in TCST.
- Writing a 0 to ERROR clears the error flops in TCST. Because it
is write 0 to clear (later controllers used write 1 to clear),
the simulator has to know whether ERROR is actually written.
- STOP ALL ignores select errors. Every other function is rejected
if there is a select error.
- An illegal operation (setting ILO) will stop the selected tape.
- A write of TCDT while the function is RALL, WALL, or WTMK clears
DONE (READY). RALL should not be included, but it saved a gate
not to prevent it.
- Because DONE (READY) may not be clear when an operation completes
and DONE (READY) is set, the DT_SETDONE must test for DONE (READY)
not being already set.
ASCII mode for the paper tape reader and punch didn't <quite> work.
In ASCII mode, the <simulator> must create the leader and trailer. The
leader was already there. There shouldn't be nulls in an ASCII file. The
whole point is to be able to prepare and look at input and output files
with a normal text editor.
So this version should work right. It "autogens" trailer more or less
forever. It doesn't really need to return a STOP code on EOF, but users
would probably forget to put form feed at the end, so it doesn't hurt.
1. Implemented Expensive Typewriter mode for TTO.
2. Added ASCII conversion on paper tape punch as well as reader.
3. Changed conversion tables to recognize form feed (014) as FIODEC STOP.
