initial concept of ROM versioning, still needs quite some work

c64/kernal/panic.s

@@ -0,0 +1,61 @@
+
+//
+// Something terrible happened - show the panic screen
+//
+
+// .A = 0 - just panic, no extra message
+// .A = 1 - ROM version mismatch
+
+panic:
+
+	sei
+	pha
+
+	jsr IOINIT
+	jsr setup_vicii
+	jsr clear_screen
+
+	// XXX disable NMIs
+
+	ldx #$14
+	ldy #$0E
+	jsr plot_set
+
+	ldx #__MSG_KERNAL_PANIC
+	jsr print_kernal_message
+
+	pla
+	beq kernal_panic_infinite_loop
+	pha
+
+	ldx #$02
+	ldy #$02
+	jsr plot_set
+
+	pla
+	pha
+	jsr print_hex_byte
+
+	pla
+	cmp #$01
+	bne kernal_panic_infinite_loop
+
+	ldx #__MSG_KERNAL_PANIC_VERSION
+	jsr print_kernal_message
+
+kernal_panic_infinite_loop:
+	ldx #$00
+	stx VIC_EXTCOL
+
+	ldx #$80
+!:
+	dex
+	bne !-
+
+	ldx #$06
+	stx VIC_EXTCOL
+!:
+	dex
+	bne !-
+
+	beq kernal_panic_infinite_loop // branch always