finished IRQ handler, fixed cartridge startup

STATUS.md

@@ -26,7 +26,6 @@ The following ROM features are currently missing:
 * floating point routines
 * tape support
 * RS-232 support
-* NMI cartridge handling and BRK handling are not implemented yet
 * breaking Kernal routines with RUN/STOP key
 * PAL/NTSC is detected, but for now only startup banner uses the result
 

c64/aliases/,aliases_rom_cart.s

@@ -0,0 +1,5 @@
+
+	;; Cartridge ROM locations
+	.alias ICART_COLD_START    $8000 ; $8000-$8001, cartridge cold start vector
+	.alias ICART_WARM_START    $8002 ; $8002-$8003, cartridge warm start vector (RESTORE key)
+	.alias CART_SIG            $8004 ; 5 bytes, signature for cartridge detection

c64/kernal/cartridge_check.s

@@ -3,13 +3,13 @@
 cartridge_check:
 	ldx #$04
 cartridge_check_l1:
-	lda $8002,x
+	lda CART_SIG,x
 	cmp cartridge_signature,x
 	bne no_cartridge
 	dex
 	bpl cartridge_check_l1
-	jmp ($8000)
-cartridge_signature:
-	.byte $C3,$C2,$CD,$38,$30
+	sec
+	rts
 no_cartridge:
+	clc
 	rts

c64/kernal/cartridge_signature.s

@@ -0,0 +1,3 @@
+
+cartridge_signature:
+	.byte $C3,$C2,$CD,$38,$30

c64/kernal/interrupts/fe47.default_nmi_handler.s

@@ -13,7 +13,10 @@ default_nmi_handler:
 
 	;; XXX: RS-232 support is not implemented
 
-	;; XXX if cartridge present, enter it through warm start vector
+	jsr cartridge_check
+	bcc +
+	jmp (ICART_WARM_START)
+*
 
 	;; According to C64 Wiki, if STOP key is pressed, the routine assumes warm start request
 

c64/kernal/interrupts/irq_handler.s

@@ -15,9 +15,14 @@ irq_handler:
 	tya
 	pha
 
-	;; XXX check if caused by BRK, react accordingly
+	;; Check if caused by BRK
 
-	;; Call interrupt routine (only if initialised)
+	tsx
+	lda $0104, x ; get the pre-interrupt processor state
+	and #$10
+	bne irq_handler_brk
+
+	;; Not caused by BRK - call interrupt routine (only if initialised)
 	lda CINV
 	ora CINV+1
 	beq +
@@ -25,3 +30,9 @@ irq_handler:
 *
 	;; Vector not initialized - call default interrupt routine
 	jmp default_irq_handler
+
+irq_handler_brk:
+
+	;; Interrupt caused by BRK
+	jmp (CBINV)
+

c64/kernal/reset_entry.s

@@ -13,7 +13,9 @@ reset_entry:
 
 	; C64 PRG p269
 	jsr cartridge_check
-
+	bcc +
+	jmp (ICART_COLD_START)
+*
 	; The following routine is based on reading the public KERNAL jumptable routine
 	; list, and making unimaginative assumptions about what should be done on reset.
 	; Initialising IO is obviously required.  also indicated by c64 prg p269.