From c7f643623d9f99436335e92733bd72db69b6494c Mon Sep 17 00:00:00 2001
From: Ivan Izaguirre <ivanizag@gmail.com>
Date: Sun, 6 Dec 2020 17:16:57 +0100
Subject: [PATCH] Extra cycle when brancing on conditional jumps. Fixes Sammy
 Lighfoot woz loadind.

---
 core6502/execute.go    | 19 +++++++++++++------
 core6502/operations.go |  1 +
 storage/disketteWoz.go |  2 +-
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/core6502/execute.go b/core6502/execute.go
index cef1c12..d55f7f7 100644
--- a/core6502/execute.go
+++ b/core6502/execute.go
@@ -17,12 +17,15 @@ const (
 
 // State represents the state of the simulated device
 type State struct {
-	reg       registers
-	mem       Memory
-	cycles    uint64
-	opcodes   *[256]opcode
-	trace     bool
-	lineCache []uint8
+	opcodes *[256]opcode
+	trace   bool
+
+	reg    registers
+	mem    Memory
+	cycles uint64
+
+	extraCycle bool
+	lineCache  []uint8
 	// We cache the allocation of a line to avoid a malloc per instruction. To be used only
 	// by ExecuteInstruction(). 2x speedup on the emulation!!
 }
@@ -76,6 +79,10 @@ func (s *State) ExecuteInstruction() {
 	}
 	opcode.action(s, s.lineCache, opcode)
 	s.cycles += uint64(opcode.cycles)
+	if s.extraCycle {
+		s.cycles++
+		s.extraCycle = false
+	}
 	if s.trace {
 		fmt.Printf("%v, [%02x]\n", s.reg, s.lineCache[0:opcode.bytes])
 	}
diff --git a/core6502/operations.go b/core6502/operations.go
index 0c8f5d9..405de53 100644
--- a/core6502/operations.go
+++ b/core6502/operations.go
@@ -76,6 +76,7 @@ func buildOpUpdateFlag(flag uint8, value bool) opFunc {
 func buildOpBranch(flag uint8, test bool) opFunc {
 	return func(s *State, line []uint8, opcode opcode) {
 		if s.reg.getFlag(flag) == test {
+			s.extraCycle = true
 			address := resolveAddress(s, line, opcode)
 			s.reg.setPC(address)
 		}
diff --git a/storage/disketteWoz.go b/storage/disketteWoz.go
index 51d8b29..fceb051 100644
--- a/storage/disketteWoz.go
+++ b/storage/disketteWoz.go
@@ -18,7 +18,7 @@ Emulation status for the disk used on the reference:
 		- *** Commando: Not working
 		- Planetfall: Working
 		- Rescue Raiders: Working
-		- *** Sammy Lightfoot: Not working
+		- Sammy Lightfoot: Working (failed if no 6502 extra cycle is added on branches done)
 		- Stargate: Working
 	- Cross track sync
 		- *** Blazing Paddles: Not working