Add a vm6502 variant

defines.s

@@ -25,6 +25,9 @@ AIM65 := 1
 .elseif .def(sym1)
 SYM1 := 1
 .include "defines_sym1.s"
+.elseif .def(vm6502)
+VM6502 := 1
+.include "defines_vm6502.s"
 .endif
 
 .ifdef CONFIG_2C

defines_vm6502.s

@@ -0,0 +1,22 @@
+; Inspired by https://github.com/beneater/msbasic
+
+; configuration
+CONFIG_2A := 1
+
+CONFIG_SCRTCH_ORDER := 2
+
+; zero page
+ZP_START1 = $00
+ZP_START2 = $0A
+ZP_START3 = $60
+ZP_START4 = $6B
+
+; extra/override ZP variables
+USR := GORESTART
+
+; constants
+SPACE_FOR_GOSUB := $3E
+STACK_TOP := $FA
+WIDTH := 40
+WIDTH2 := 30
+RAMSTART2 := $0400

extra.s

@@ -24,6 +24,10 @@
 .include "aim65_extra.s"
 .endif
 
+.ifdef VM6502
+.include "vm6502_extra.s"
+.endif
+
 .ifdef SYM1
         .byte   0,0,0
-.endif
+.endif

header.s

@@ -11,3 +11,6 @@
 .ifdef SYM1
         jmp     PR_WRITTEN_BY
 .endif
+.ifdef VM6502
+        jmp COLD_START
+.endif

iscntc.s

@@ -26,4 +26,7 @@
 .ifdef SYM1
 .include "sym1_iscntc.s"
 .endif
+.ifdef VM6502
+.include "vm6502_iscntc.s"
+.endif
 ;!!! runs into "STOP"

make.sh

@@ -2,7 +2,7 @@ if [ ! -d tmp ]; then
 	mkdir tmp
 fi
 
-for i in cbmbasic1 cbmbasic2 kbdbasic osi kb9 applesoft microtan aim65 sym1; do
+for i in cbmbasic1 cbmbasic2 kbdbasic osi kb9 applesoft microtan aim65 sym1 vm6502; do
 
 echo $i
 ca65 -D $i msbasic.s -o tmp/$i.o &&

vm6502.cfg

@@ -0,0 +1,19 @@
+MEMORY {
+	ZP:		start = $0000, size = $0100, type = rw;
+	BASROM:		start = $C000, size = $3F00, fill = no, file = %O;
+	DUMMY:		start = $0000, size = $00FF, file = "";
+}
+
+SEGMENTS {
+	ZEROPAGE:	load = ZP, type = zp;
+	HEADER:		load = BASROM,	type = ro;
+	VECTORS:	load = BASROM,	type = ro;
+	KEYWORDS:	load = BASROM,	type = ro;
+	ERROR:		load = BASROM,	type = ro;
+	CODE:		load = BASROM,	type = ro;
+	CHRGET:		load = BASROM,	type = ro;
+	INIT:		load = BASROM,	type = ro;
+	EXTRA:		load = BASROM,	type = ro;
+	DUMMY:		load = DUMMY; # don't include
+}
+

vm6502_extra.s

@@ -0,0 +1,49 @@
+; Inspired by https://github.com/beneater/msbasic
+
+; TODO implement
+
+LOAD:
+                rts
+
+SAVE:
+                rts
+
+
+; On return, carry flag indicates whether a key was pressed
+; If a key was pressed, the key value will be in the A register
+;
+; Modifies: flags, A
+MONRDKEY:
+CHRIN:
+;                lda     ACIA_STATUS
+;                and     #$08
+;                beq     @no_keypressed
+;                lda     ACIA_DATA
+;                jsr     CHROUT			; echo
+;                sec
+;                rts
+;@no_keypressed:
+                clc
+                rts
+
+
+; Output a character (from the A register)
+;
+; Modifies: flags
+MONCOUT:
+CHROUT:
+;                pha
+;                sta     ACIA_DATA
+;                lda     #$FF
+;@txdelay:       dec
+;                bne     @txdelay
+;                pla
+                rts
+
+; TODO set up reset vector
+
+;.segment "RESETVEC"
+;                .word   $0F00           ; NMI vector
+;                .word   RESET           ; RESET vector
+;                .word   $0000           ; IRQ vector
+

vm6502_iscntc.s

@@ -0,0 +1,17 @@
+; Inspired by https://github.com/beneater/msbasic
+
+; TODO implement
+
+ISCNTC:
+;        jsr MONRDKEY
+;        bcc not_cntc
+;        cmp #3
+;        bne not_cntc
+;        jmp is_cntc
+;
+;not_cntc:
+        rts
+
+;is_cntc:
+;        ; Fall through
+