189 lines
5.7 KiB
Plaintext
189 lines
5.7 KiB
Plaintext
.bp
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.np
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.ce
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CHAPTER 7 - CUSTOMIZING DOS
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.sp1
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Although DOS usually provides most of
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the functionality needed by the BASIC
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or assembly language programmer, at
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times a custom change is required.
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Making changes to your copy of DOS
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should only be undertaken when
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absolutely necessary, since new
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versions of DOS are released from
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time to time, and the job of moving
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several patches to a new version of
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DOS every few months can become a
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burden. In addition, wholesale
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modification of DOS without a clear
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understanding of the full
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implications of each change can
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result in an unreliable system.
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.sp1
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SLAVE VS MASTER PATCHING
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The usual procedure for making
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changes to DOS involves "patching"
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the object or machine language code
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in DOS. Once a desired change is
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identified, a few instructions are
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stored over other instructions within
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DOS to modify the program. There are
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three levels at which changes to DOS
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may be applied.
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.sp1
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1 - A patch can be made to the DOS
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in memory. If this is done, a later
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reboot will cause the change to "fall
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out" or be removed.
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.sp1
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2 - A patch of the first type can be
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made permanent by initializing a\x1f?O7O?K'7s';;\x44\x4d\x08\x5a\x5d\x46\x46\x41\x46\x4f\x08\x5c\x40\x4d\x08\x58\x497#+''O\x87\x8f\x93oc\x97++3c77+'##37#g'7#'3#7g'g7+'3#K#/7/#33#g3/3/g'g'+7?g+#g\x83\x8b\x97g++g37''/7Kwkgwkg'+#gwg3//'/g'++3'/+7g3/#g7'3'h.
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Each time this newly created diskette
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is booted the patched version of DOS
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will be loaded. Also, any slave
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diskettes created by that diskette
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will also contain the patched version
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of DOS.
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.bp
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3 - The patch is applied directly to
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a master diskette. This is somewhat
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more complicated. Either the patch
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may be made to the image of DOS on
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the first three tracks of a master
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diskette using a zap program, or
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MASTER CREATE may be used to write
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the changed copy of DOS to a new
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diskette. The following procedure may
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be followed to do this:
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.br
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BLOAD MASTER CREATE
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Get into the monitor (CALL -151)
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Store a $4C at location $80D (80D:4C)
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Execute MASTER CREATE (800G)
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When MASTER CREATE finishes loading the DOS image
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it will exit. You may use the monitor to make
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changes in the image. MASTER CREATE loads DOS
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into memory at $1200 such that Boot 2 (RWTS) is
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loaded first, followed by the main part of DOS
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starting at $1C00.
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When all patches have been made, reenter MASTER CREATE
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at location $82D (82DG).
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Complete the MASTER CREATE update normally. The
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resulting diskette will have the patches applied.
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.br
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This procedure will work for versions 3.2, 3.2.1, and 3.3 of
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DOS.
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.sp1
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.ne5
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AVOIDING RELOAD OF LANGUAGE CARD
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A rather annoying addition to DOS 3.3
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was a patch to the Boot 2 code to
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store a binary zero in the first byte
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of the Language Card, forcing DOS to
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reload BASIC (either INTEGER or
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APPLESOFT) for every boot, whether or
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not the machine was just powered up.
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When the machine is first powered up
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this patch is not necessary, since
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the first byte of the Language Card
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does not appear to DOS to be either
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BASIC, and it will reload the card
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anyway. On subsequent reboots, more
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often than not, a good copy of BASIC
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already resides in the Language Card
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and this patch results in a LANGUAGE
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NOT AVAILABLE error message after
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booting a slave diskette. Presumably
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the patch was added for version 3.3
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to allow for the eventual possibility
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that a language like PASCAL whose
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first byte of code just happens to
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match one of the BASICs would cause
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strange results in DOS. If the user
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always powers the machine off and on
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between using DOS and any other
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system, the patch may be removed as
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follows.
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.bp
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At $BFD3 (48K) is a STA instruction which
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stores a zero on the Language Card.
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This instruction must be made into
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three no-operation instructions:
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BFD3:EA EA EA
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.br
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A slave diskette may then be INITed
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using this modified version of DOS
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and that diskette will have the
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patch in its DOS. The address of the
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store instruction for a 32K DOS is
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7FD3 and for a 16K DOS is 3FD3.
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.sp1
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INSERTING A PROGRAM BETWEEN DOS AND ITS BUFFERS
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Once in a while it is useful to find
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a "safe" place to load a machine
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language program (a printer driver,
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perhaps) where BASIC and DOS
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can never walk over it, even if DOS
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is coldstarted. If the program is
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less than 200 bytes long, $300 is a
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good choice. For larger programs,
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it is usually better to "tuck" the
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program in between DOS and its
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buffers (assuming the program is
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relocatable and will run at that
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location). To do this, load the
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program into low RAM, copy it to high
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RAM right below $9D00 (for a 48K
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machine), over the top of DOS's
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buffers, change the first buffer
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address at $9D00 to point below your
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program, (remember to allow 38 extra
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bytes for the filename and link fields)
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and JMP to $3D3 (DOS
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COLDSTART). This will cause DOS to
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rebuild its buffers below your
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program and "forget" about the memory
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your program occupies until the next
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time DOS is booted. Of course, BASIC
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can not get at that memory either,
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since its HIMEM is below the DOS
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buffers.
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.bp
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BRUN OR EXEC THE HELLO FILE
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Ordinarily, when DOS finishes booting
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into memory, it performs a RUN
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command on the HELLO file in its file
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name buffer (left there by the INIT
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command which wrote DOS to the
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diskette). To change the RUN command
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to a BRUN or an EXEC, apply the
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following patch to DOS (48K):
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.sp1
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9E42:34 (for BRUN)
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..or..
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9E42:14 (for EXEC)
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.sp1
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.ne5
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REMOVING THE PAUSE DURING A LONG CATALOG
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Normally, when a CATALOG command is
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done on a disk with many files, DOS
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will pause every time the screen
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fills with names to allow the user
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time to see them all.
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By pressing any key
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the CATALOG continues. If this pause
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is undesirable, apply the following
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patch to DOS (48K):
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.sp1
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AE34:60
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.br
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.bp
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.st waiting for ch8 diskette
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.nx ch8
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