28 lines
1.2 KiB
Markdown
28 lines
1.2 KiB
Markdown
The 8Mhz IBM PC AT 5170
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I just added my first [8Mhz IBM PC AT](/devices/pc/machine/5170/ega/1152kb/rev3/) machine configuration
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to the list of [IBM PC Machine Configurations](/devices/pc/machine/), and not surprisingly, the new machine
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fails to boot.
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This machine uses the 3rd [ROM BIOS](/devices/pc/bios/5170/) that IBM released for the PC AT, a revision that
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included support for 3.5-inch 1.44Mb diskettes -- which will be nice, because I have a number of 1.44Mb diskette
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images I would like to be able to read in a PCjs machine.
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Since machines with this BIOS also ran at 8Mhz, I've bumped the CPU speed up to 8,000,000 cycles/second.
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It'll be interesting to see whether this BIOS also increased any of its hard-coded timing delay-loops as a result.
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Anyway, when I enabled ChipSet I/O port messages in the Debugger:
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m chipset on
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m port on
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I can see that the BIOS Power-On Self Test (POST) progresses nicely until it starts generating lots of port 0x61
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activity:
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chipset.inPort(0x0061,8042_RWREG): 0x30 at F000:05A8
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chipset.inPort(0x0061,8042_RWREG): 0x20 at F000:05AE
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I know what I'm going to be doing this afternoon now.
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*[@jeffpar](http://twitter.com/jeffpar)*
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*October 13, 2014*
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