variable support cleanup

src/basic/engine_runtime/do_new_clr_restore.s

@@ -0,0 +1,110 @@
+// #LAYOUT# STD *       #TAKE
+// #LAYOUT# M65 *       #TAKE
+// #LAYOUT# X16 BASIC_0 #TAKE
+// #LAYOUT# *   *       #IGNORE
+
+
+// See https://www.c64-wiki.com/wiki/Memory_(BASIC) for BASIC memory organization
+
+
+do_new:	
+
+#if (ROM_LAYOUT_M65 && SEGMENT_BASIC_0)
+
+	jsr     map_BASIC_1
+	jsr_ind VB1__do_new
+	jmp     map_NORMAL
+
+do_clr:
+
+	jsr     map_BASIC_1
+	jsr_ind VB1__do_clr
+	jmp     map_NORMAL
+
+do_restore:
+
+	jsr     map_BASIC_1
+	jsr_ind VB1__do_restore
+	jmp     map_NORMAL
+
+#else
+
+	// See Computes Mapping the Commodore 64 - page 96
+
+	ldy #$00
+	tya
+	sta (TXTTAB),y
+	iny
+	sta (TXTTAB),y
+
+	// The book does not mention this, but IMHO it is necessary to initialize VARTAB here too
+
+	clc
+	lda TXTTAB+0
+	adc #$02
+	sta VARTAB+0
+	lda TXTTAB+1
+	adc #$00
+	sta VARTAB+1
+
+do_clr:
+
+	// See Computes Mapping the Commodore 64 - page 96
+
+	// XXX check if original ROM does this too
+	jsr JCLALL
+
+	lda MEMSIZ+0
+	sta FRETOP+0 
+	lda MEMSIZ+1
+	sta FRETOP+1 
+
+	// The book is not precise here $31-$32 is definitely not the end of BASIC text
+
+	lda VARTAB+0
+	sta ARYTAB+0
+	sta STREND+0
+
+	lda VARTAB+1
+	sta ARYTAB+1
+	sta STREND+1	
+
+	// This is a good place to reset the temporary string stack
+
+	lda #$19
+	sta TEMPPT
+	lda #$16
+	sta LASTPT
+
+	// FALLTROUGH (confirmed on real C64 that CLR indeed resets DATPTR)
+
+do_restore:
+
+	// See Computes Mapping the Commodore 64 - page 98
+	// Initial DATPTR value checked on real C64
+
+#if HAS_OPCODES_65CE02
+
+	lda TXTTAB+0
+	sta DATPTR+0
+	lda TXTTAB+1
+	sta DATPTR+1
+
+	dew DATPTR
+
+#else
+
+	sec
+	lda TXTTAB+0
+	sbc #$01
+	sta DATPTR+0
+	lda TXTTAB+1
+	sbc #$00
+	sta DATPTR+1
+
+#endif
+
+	rts
+
+
+#endif // ROM layout