From 021c9b3189ced35a1dde1be4a6c297bc781bfa58 Mon Sep 17 00:00:00 2001
From: FeralChild64 <you@example.com>
Date: Wed, 11 Sep 2019 21:50:48 +0200
Subject: [PATCH] size-optimized cartridge check

---
 c64/kernal/cartridge_check.s                     | 10 ++++------
 c64/kernal/interrupts/fe47.default_nmi_handler.s |  2 +-
 c64/kernal/reset_entry.s                         |  5 +++--
 3 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/c64/kernal/cartridge_check.s b/c64/kernal/cartridge_check.s
index 09a58216..f74cfeaa 100644
--- a/c64/kernal/cartridge_check.s
+++ b/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
diff --git a/c64/kernal/interrupts/fe47.default_nmi_handler.s b/c64/kernal/interrupts/fe47.default_nmi_handler.s
index fdf3115c..2c89e4a0 100644
--- a/c64/kernal/interrupts/fe47.default_nmi_handler.s
+++ b/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)
 !:
 
diff --git a/c64/kernal/reset_entry.s b/c64/kernal/reset_entry.s
index 9eb9eca7..626e6d72 100644
--- a/c64/kernal/reset_entry.s
+++ b/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.