[openMSX-bugs] [ openmsx-Bugs-3212350 ] Bit6 and 7 of PSG reg#7 stuck to 10xxxxxxb

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Bugs item #3212350, was opened at 2011-03-15 02:44
Message generated for change (Comment added) made by bifimsx
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: FRS (sd-snatcher)
Assigned to: Nobody/Anonymous (nobody)
Summary: Bit6 and 7 of PSG reg#7 stuck to 10xxxxxxb

Initial Comment:
Wanting to help Whizzy and avoid that some rare MSX gets damaged, I decided to debug BomberMan2 for the unsafe bits set on PSG as reported here,
http://www.msx.org/Bomberman-2-for-download.newspost5745.html

I did set one watchpoint to discover were the game was setting the unsafe condition:

debug set_watchpoint write_io 0xA1 { [ expr [ debug read PSG\ regs 7 ] & 0xC0 ] != 0x80 }

Then I boot the game, openMSX shows the PSG warning on the stdout, but no break occurs. If I check the PSG' s R#7, it shows 0xBF, which is a safe value.

I tried changing the reg#7 manually to force the breakpoint to occur:

debug write PSG\ regs 7 0x3F

But reading it back again... 

debug read PSG\ regs 7

...and it returns 191 (0xBF), which means that the register is being forced to 10xxxxxxb internally to the emulator, which don't makes sense, because the PSG is a generic chip and the emulator would never get damaged. This 10xxxxxxb overriding it turns impossible to use watchpoints to quicly locate such a dangerous problem...


Test environment: openMSX-0.8.1 on Mac OS-X v10.6.6
Emulated machine: Panasonic FS-A1WSX (expanded to 512KB RAM)


BTW, this unsafe PSG problem is another one of the things that made me think of the AcidTests for the MSX standard... (See #3209252)


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Comment By: Albert Beevendorp (bifimsx)
Date: 2011-03-15 06:22

Message:
I have an updated version of the file in question with some extra's. This
version is currently in internal beta. It also fixes this particular bug.

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=421861&aid=3212350&group_id=38274