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On C64, VIC-20 and Plus/4, the conio library PLOT routine uses direct calls into the Kernal, including the Kernal PLOT routine that we're replacing. These were previously hardcoded addresses; we change these to use the symbols for those routines defined in cbm_kernal.inc. (This changes no functionality.) To do this, we need to import cbm_kernal.inc in a namespace so we don't have a collision between the PLOT that we're defining and the Kernal definition. We also add a UPDCRAMPTR symbol (used by kplot for VIC-20 and C64) to the direct entry kernal routines in in cbm_kernal.inc, and expand the comments describing what the "direct entry" Kernal routines are. <greg.king5@verizon.net> (GitHub: greg-king5) came up with this idea and did initial testing of it. This has been tested on VICE xvic, x64 and xplus4 emulators with a program that does a cputs() call (github.com/0cjs/vic20cc65) to confirm that it works the same way after as it did before.
23 lines
547 B
ArmAsm
23 lines
547 B
ArmAsm
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; Ullrich von Bassewitz, 2002-12-09
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; PLOT replacement function for the VIC20. The kernal function does not set
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; the pointer to the color RAM correctly.
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.export PLOT
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.scope KERNAL
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.include "cbm_kernal.inc"
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.endscope
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.proc PLOT
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bcs @L1
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jsr KERNAL::PLOT ; Set cursor position using original ROM PLOT
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jmp KERNAL::UPDCRAMPTR ; Set pointer to color RAM to match new cursor position
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@L1: jmp KERNAL::PLOT ; Get cursor position
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.endproc
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