begin implementing basic text manipulation routines.

c64/basic/under_rom_routines.s

@@ -0,0 +1,57 @@
+	;; IMPORTANT:
+	;; These routines lengths cannot be changed without changing
+	;; the aliases for peek_under_roms, poke_under_roms etc
+	;; in ,aliases.s.
+	;; Thus those addresses are expressed using formulae.
+
+install_ram_routines:
+	;; Copy routines into place
+	ldx #ram_routines_len-1
+*
+	lda ram_routines_start,x
+	sta tiny_nmi_handler,x
+	dex
+	bpl -
+
+	;; Point NMI handler to tiny_nmi_handler
+	lda #<tiny_nmi_handler
+	sta $FFFE
+	lda #>tiny_nmi_handler
+	sta $FFFF
+
+	rts
+	
+ram_routines_start:	
+
+tiny_nmi_handler_routine:
+	inc missed_nmi_flag
+	rti
+
+peek_under_roms_routine:
+	stx peek_under_roms+7 	;Offset of arg of lda ($00),y
+	jsr memmap_allram
+	lda ($00),y
+	jmp memmap_normal
+
+poke_under_roms_routine:
+	stx poke_under_roms+7 	;Offset of arg of lda ($00),y
+	jsr memmap_allram
+	sta ($00),y
+	;; FALL THROUGH
+memmap_normal_routine:
+	pha
+	lda #$37
+	sta $01
+	pla
+	cli
+	rts
+
+memmap_allram_routine:
+	sei
+	lda #$04
+	sta $01
+	rts
+
+ram_routines_end:
+	.alias ram_routines_len ram_routines_end-ram_routines_start
+