size-optimized cartridge check

c64/kernal/cartridge_check.s

@@ -1,15 +1,13 @@
 // c64 prg p263
 
 cartridge_check:
-	ldx #$04
+	ldx #$05
 cartridge_check_l1:
-	lda CART_SIG,x
-	cmp cartridge_signature,x
+	lda CART_SIG-1,x
+	cmp cartridge_signature-1,x
 	bne no_cartridge
 	dex
-	bpl cartridge_check_l1
-	sec
+	bne cartridge_check_l1
 	rts
 no_cartridge:
-	clc
 	rts

c64/kernal/interrupts/fe47.default_nmi_handler.s

@@ -16,7 +16,7 @@ default_nmi_handler:
 	// XXX confirm NMIs from CIA, or no other NMI will arrive!
 
 	jsr cartridge_check
-	bcc !+
+	bne !+
 	jmp (ICART_WARM_START)
 !:
 

c64/kernal/reset_entry.s

@@ -3,11 +3,12 @@
 
 
 reset_entry:
+
 	// The GPL program at https://github.com/Klaus2m5/6502_65C02_functional_tests/blob/master/6502_functional_test.a65
 	// uses the following initial reset sequence
 	// affirmed by c64 PRG p269
 	cld
-	ldx #$ff
+	ldx #$FF
 	txs
 	sei
 
@@ -18,7 +19,7 @@ reset_entry:
 
 	// C64 PRG p269
 	jsr cartridge_check
-	bcc !+
+	bne !+
 	jmp (ICART_COLD_START)
 !:
 	// Initialising IO is obviously required. Also indicated by c64 prg p269.