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vc83 as ac6502 cartridge #231

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Merged
willisblackburn merged 3 commits into from
Apr 25, 2026
Merged

vc83 as ac6502 cartridge #231

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cabb0a6
Configure vc83 as a ac6502 cartridge
acwright Apr 24, 2026
53720c9
Add break detection
acwright Apr 24, 2026
0cceca5
Add ac6502 extensions
acwright Apr 24, 2026
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57 changes: 41 additions & 16 deletions ac6502/ac6502.cfg
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Original file line number Diff line number Diff line change
@@ -1,27 +1,52 @@
# SPDX-FileCopyrightText: 2022-2026 Willis Blackburn
#
# SPDX-License-Identifier: MIT
#
# Linker configuration for VC83 BASIC as an ac6502 cartridge.
#
# Cartridge ROM overlays $C000-$FFFF. The BIOS Kernal jump table at
# $A000 and its implementation at $A100-$B7FF remain accessible, as
# does the character-set ROM at $B800-$BFFF. BASIC runs from ROM and
# uses RAM at $0800-$7FFF for its workspace (buffers, stacks, BSS) and
# the user program / variables / string heap.
#
# Zero page layout (per 6502-BIOS/BIOS.inc):
# $00-$03 System pointers (BIOS)
# $04-$23 Reserved by native BIOS BASIC (unused here)
# $24-$35 System scratch (CF, XFER, XModem, Monitor)
# $3A-$FF Free for user programs -> VC83 BASIC zero page lives here
#
# See https://github.com/acwright/6502 for more info

FEATURES {
STARTADDRESS: default = $0800;
}
SYMBOLS {
__STACKSIZE__: type = weak, value = $0000;
__ZPSTART__: type = weak, value = $003A;
__ZPSIZE__: type = weak, value = $00C6;
__RAM_START__: type = weak, value = $0800;
__HIMEM__: type = weak, value = $8000;
__ROM_START__: type = weak, value = $C000;
}
MEMORY {
ZEROPAGE: file = "", start = $0080, size = $0080;
MAIN: file = %O, start = %S, size = __HIMEM__ - %S, define = yes;
BSS: file = "", start = __ONCE_RUN__, size = __HIMEM__ - __ONCE_RUN__;
ZEROPAGE: file = "", start = __ZPSTART__, size = __ZPSIZE__;
MAIN: file = "", start = __RAM_START__, size = __HIMEM__ - __RAM_START__, define = yes;
# AT28C256 is 32 KB. The chip's lower half ($0000-$3FFF in the file)
# is filled with zeros; the upper half ($4000-$7FFF) carries the
# cartridge ROM that the CPU sees at $C000-$FFFF. PAD is the first
# region written to the output file so the linker emits zeros there.
PAD: file = %O, start = $8000, size = $4000, fill = yes, fillval = $00;
ROM: file = %O, start = __ROM_START__, size = $FFFA - __ROM_START__, fill = yes, fillval = $00;
VECTORS: file = %O, start = $FFFA, size = $0006, fill = yes, fillval = $00;
}
SEGMENTS {
ZEROPAGE: load = ZEROPAGE, type = zp;
STARTUP: load = MAIN, type = ro;
CODE: load = MAIN, type = ro;
VEC: load = MAIN, type = ro, define = yes;
XVEC: load = MAIN, type = ro, define = yes;
FUNC: load = MAIN, type = ro, define = yes;
XFUNC: load = MAIN, type = ro, define = yes;
PARSER: load = MAIN, type = ro;
ONCE: load = MAIN, type = ro, define = yes;
BSS: load = BSS, type = bss, define = yes;
ZEROPAGE: load = ZEROPAGE, type = zp;
STARTUP: load = ROM, type = ro;
CODE: load = ROM, type = ro;
VEC: load = ROM, type = ro, define = yes;
XVEC: load = ROM, type = ro, define = yes;
FUNC: load = ROM, type = ro, define = yes;
XFUNC: load = ROM, type = ro, define = yes;
PARSER: load = ROM, type = ro;
ONCE: load = ROM, type = ro, define = yes;
BSS: load = MAIN, type = bss, define = yes, align = $100;
VECTORS: load = VECTORS, type = ro;
}
94 changes: 87 additions & 7 deletions ac6502/ac6502.inc
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Original file line number Diff line number Diff line change
@@ -1,13 +1,93 @@
; SPDX-FileCopyrightText: 2022-2026 Willis Blackburn
;
; SPDX-License-Identifier: MIT
;
; ac6502 target include -- symbolic names for BIOS Kernal routines and
; system variables used by VC83 BASIC. See 6502-BIOS/BIOS.inc for the
; full documentation of the Kernal jump table.
;
; See https://github.com/acwright/6502-BIOS for more info

BAS_LINBUF_SIZE = 240

CH_CTRLC = $03
CH_BEL = $07
CH_BKSP = $08
CH_LF = $0A
CH_CR = $0D
CH_ESC = $1B
CH_SPACE = $20
CH_DEL = $7F

; --- Zero-page system pointers (BIOS) ---
STR_PTR := $02 ; $02-$03 - BIOS string pointer

; --- BIOS Kernal jump table ($A000-$A0FF) ---
Chrout := $A000 ; Output character (routed by IO_MODE)
Chrin := $A003 ; Non-blocking input char (C=1 if available)
WriteBuffer := $A006
ReadBuffer := $A009
BufferSize := $A00C
SetIOMode := $A00F
GetIOMode := $A012
InitVideo := $A015
VideoClear := $A018
VideoPutChar := $A01B
VideoSetCursor := $A01E
VideoGetCursor := $A021
VideoScroll := $A024
VideoSetColor := $A027
VideoChroutRaw := $A02A
InitSID := $A02D
Beep := $A030
SidPlayNote := $A033
SidSilence := $A036
SidSetVolume := $A039
FsLoadFile := $A03C
FsSaveFile := $A03F
FsDeleteFile := $A042
InitKB := $A045
ReadJoystick1 := $A048
ReadJoystick2 := $A04B
InitSC := $A04E
SerialChrout := $A051
XModemLoad := $A054
XModemSave := $A057
RtcReadTime := $A05A
RtcReadDate := $A05D
RtcWriteTime := $A060
RtcWriteDate := $A063
RtcReadNVRAM := $A066
RtcWriteNVRAM := $A069
StReadSector := $A06C
StWriteSector := $A06F
StWaitReady := $A072
SysDelay := $A075
KernalInit := $A078 ; Initialize all hardware; caller resets SP, must CLI after
KernalVersion := $A07B

; --- System RAM variables used here ---
IRQ_PTR := $0300
BRK_PTR := $0302
NMI_PTR := $0304
IO_MODE := $0306
HW_PRESENT := $030D
BOOT_VECTOR := $035B

BAS_LINBUF_SIZE = 240
; Legacy aliases used by earlier ac6502 code.
CHROUT := Chrout
CHRIN := Chrin

CH_CR = $0D ; Carriage return
CH_LF = $0A ; Line feed
CH_SPACE = $20 ; Space
CH_BKSP = $08 ; Backspace
; --- HW_PRESENT bit masks ---
HW_RAM_L = %00000001
HW_RAM_H = %00000010
HW_RTC = %00000100
HW_CF = %00001000
HW_SC = %00010000
HW_GPIO = %00100000
HW_SID = %01000000
HW_VID = %10000000

CHROUT := $A000
CHRIN := $A003
; --- RTC / storage RAM variables used by kernal routines ---
RTC_BUF_CENT := $030B ; Century register for RTC read/write
RAM_BANK_L := $83FF ; Write-only bank latch for low RAM card
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