The extra special Christmas Gift update is available:
In releases before the front panel LED's got an update at every M1 cycle only, which looks
nice but is not accurate. With this release the LED's are update at every machine cycle for
both CPU's, and some status display bugs have been fixed also. Now also such programs
like the killbits game from the MITS manual show the moving light on the upper 8 bits
of the address bus, I left a copy for you in the altairsim directory.
Then single stepping so far only worked at every M1, so one would step from instruction
to instruction. With this release single stepping also works at every machine cycle, so you
can see exactly what the CPU's are doing.
The Altair 8800 has a switch INT which now is connected to the CPU interrupt line. A dumb
switch won't put an instruction onto the data bus on interrupt acknowledge, so data bus is
all high = 0xff, that is the RST 7 instruction which will get executed then.
If you would like to singe step through the interrupt machine cycles you can try something
0000 ORG 0
0000 310004 LXI SP,0400H
0003 FB EI
0004 76 LOOP: HLT
0005 C30400 JMP LOOP
0038 ORG 38H
0038 FB EI
0039 C9 RET
and flip INT at any time to cause the interrupt.
Have fun with this,