Quoted from slochar:then the first section of code (the sta $93) turns OFF the LED.
Actually the MPU LED is switched off at line 5862, not 5839.
I hope it's ok that I added the 6821 PIA comments:
MPU-200_Galaxy_DSM1.png(Topic ID: 261103)
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MPU-200_Galaxy_DSM1.pngQuoted from Coyote:Question: What is "J5 interrupts"? (Line 5839..)
It was a spare unused interrupt source that Bally routed (and Stern copied) to the J5 connector for future expansion, maybe an inhouse debugger as slochar mentioned - possibly some exotic sound boards in the European conversion game kits may use it.
The Stern VSU-100 speech boards are wired to this spare PIA interrupt but not from the MPU connector J5 pin 32, rather MPU J4 pin 11 which was specially wired on the MPU-200 board. The speech board uses it to notify the CPU it's busy speaking.
Quoted from slochar:probably for the sb300 to interrupt the cpu (which I don't think ever was programmed) or a for an external in-system debugger setup.
For some reason Stern added an extra pin (34) to the J5 connector that directly interrupts the CPU IRQ input without PIA control. While the programmable timer chip on the SB300 is wired to it, I don't think the feature is actually used.
Quoted from slochar:@Quench sure go ahead and correct/add as you see fit.
Cheers, I'll try to add the PIA comments in the zero crossing interrupt handler in a few days.
Quoted from slochar:Nope, too interspersed with the PIGS code.
Hmm, I see.
Besides the "game personality" code, do you find there can be a lot of system code comments that's fairly easily copy'n'pasted between games when you're documenting them?
It might be worth as you expose more PIGS command functions that you add them to your first post as a list so there's a central quick reference?
Maybe also the use of RAM locations as you determine what they're for.
1 year later
Quoted from slochar:That's interesting that they fixed it in pinmame. I think that's why I just had a devil of a time with some BGT commands in dragonfist that after some modifications worked great in pinmame, put it in the game and boom, nothing. Was driving me batty but if the 6800 emulation corrects those errors, that would explain it.
I'm the one who fixed it in MAME/PinMAME 4 years ago after discovering some of my code behaved differently between emulation and actual game hardware. So any of these emulators older than mid 2017 have the CPX bug that incorrectly configures the status flags. The only valid conditional branch instructions on a real 6800 after executing CPX are BEQ/BNE/BMI/BPL
Nice work by the way..
Quoted from slochar:So it's fixed in that it matches what the hardware does?
Yes. The previous incorrect implementation of CPX compared 16-bit values which is why BLE/BHI etc worked. The real implementation compares the upper and lower bytes separately.
If you're familiar with DIFF, I still have the PinMAME source fix I can email you.
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