70 lines
3.8 KiB
Plaintext
70 lines
3.8 KiB
Plaintext
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Apple DOS 3.1 Source Code - Notes
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****************************************************************************************
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* The initial release of DOS 3.1 had a handful of bugs, two of which were particularly
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frustrating for users. The first bug prevented the ability to successfully run the
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MASTER.CREATE program. You could INIT a slave disk just fine, but not a master
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disk. Indeed, I've confirmed this with every DOS 3.1 disk image that I could find.
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Apparently, a patch was published by a user group that fixed the issue, and that
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patch was at some point incorporated in some of the later DOS 3.1 disks that were
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distributed by Apple (it seems they didn't change the 3.1 revision number when they
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released the updated disks). Try as I might, I haven't found any differences in the
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RAWDOS binary or DOS/boot sectors on any of the disk images that I have located,
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and I haven't located any documentation that provides any details on this particular
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patch.
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With that, I studied the source for a bit and pretty quickly found what the problem
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was, and applied (what turned out to be) a simple two byte patch.
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The second bug prevented Applesoft from READ'ing or WRITE'ing lines numbered greater
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than 255. The patch that addressed this problem, while apparently not on the initial
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release of DOS 3.1, WAS found on every disk image that I have located.
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This source file, the included boot disk image, and the RAWDOS binary on the disk
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image, all incorporate these two simple patches (thus the 'Patched Release'
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reference at the top of the source file).
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* This source file obviously includes the Apple DOS RWTS low-level subroutines
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written by Steve Wozniak and Randy Wigginton. The original source listing file is
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posted on the CHM website and named "Apple_DOS_RW_30May1978.txt".
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The object code for this part of the source was compared to sectors extracted from
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an Apple DOS 3.1 master disk, as well as the RAWDOS binary distributed with DOS 3.1,
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and somewhat surprisingly only a single byte was changed. The change occurs at
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appdos31.asm source line number 4877. The delay byte in the original is $5F, and
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with DOS 3.1 it's $FF.
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Note that this source not only contains the RWTS low-level subroutines that were
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made available, but also the necessary RWTS main entry point routines. The original
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source listing for this part of RWTS has not been made available as of this writing.
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With that, I took a stab at commenting that part of the disassembled code.
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* This source file will produce a binary that is identical (with the one exception
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noted at the top of the source file) to the RAWDOS binary image that was included
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on the DOS 3.1 master disk.
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The resulting binary was placed on a DOS 3.1 master disk image and named as RAWDOS,
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the disk was booted, and then the MASTER.CREATE program was run (because we have the
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necessary patch! :)) to create a new master disk. The new disk (INIT'ed with the
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newly assembled RAWDOS binary) was tested and found to be working perfectly.
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And (just for the fun of it :)), I also placed the various components of this binary
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directly on the appropriate sectors of a disk image, set some of the initial EC3, IOB,
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and various 'MISC BUT REQD CELLS' values that are required to boot, and it also boots
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and runs just fine.
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* The disk image (Apple DOS 3.1 Master - AFS.nib) included with this archive is the
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result of running MASTER.CREATE with the assembled RAWDOS binary, and then copying
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(loading/saving) the additional files that were distributed with the DOS 3.1 master
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disk from an original 3.1 master disk image. It is in the 'nibblized' image format,
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which should be supported by most (if not all) Apple II emulators.
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Scott LaBombard
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labomb@rochester.rr.com
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12/07/2013
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