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39 lines
1.7 KiB
Plaintext
39 lines
1.7 KiB
Plaintext
Magic 12 - Show bug report
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=========================================================
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THESE ARE NOT BUGS IN DOSBOX, BUT NOTED
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=========================================================
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Memory corruption bugs:
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- If UMBs are enabled, Show will cause an "MCB list corrupted"
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message after the demo has run, when you run certain other programs
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like MEM.COM. Apparently Show overwrites 2 bytes in the
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last MCB below 640KB at segment 0x9FFF sometime during the demo.
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The 2 bytes written happen to stomp on the upper 8 bits of some
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other field and the lower 8 bits of the segment size field. Once
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the segment size is corrupted, the MCB no longer points to the
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first block in UMB, and DOSBox detects this as an "MCB list
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corrupted" error.
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Workaround:
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You can avoid this crash/memory corruption by setting 'dos mem limit'
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to a value less than 640 (such as 'dos mem limit=639') to mark off
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the last 1KB of lower conventional memory as off-limits. If the demo
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corrupts the bytes at segment 0x9FFF, it will have no effect and
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DOSBox will no longer crash with "MCB list corrupted". It's possible
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nobody ever caught the bug because most BIOSes by that point had
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started taking the top 1KB under 640KB for the EBDA (extended BIOS
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data area) and the corruption merely affected the unused trailing
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end of it.
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==========================================================
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THESE BUGS ARE FIXED
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==========================================================
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VGA raster bugs:
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- 18-bit RGB highcolor hacked modes work except for minor errors
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in linewise rendering that cause visible "stripes" in the output
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(but only if the cycles count is greater than about 9000).
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