From 9f12ce2fb8c701b199ee28eb992a67f8cbd46e99 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Wed, 20 Jan 2021 20:16:55 -0500
Subject: [PATCH] Corrects RTS, adds the remainder of the direct flag
 manipulations.

---
 InstructionSets/M50740/Executor.cpp | 10 +++++++---
 InstructionSets/M50740/Executor.hpp |  8 ++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/InstructionSets/M50740/Executor.cpp b/InstructionSets/M50740/Executor.cpp
index 20033027c..69cff9cc7 100644
--- a/InstructionSets/M50740/Executor.cpp
+++ b/InstructionSets/M50740/Executor.cpp
@@ -105,7 +105,7 @@ template <Operation operation, AddressingMode addressing_mode> void Executor::pe
 #define next8()		memory_[(program_counter_ + 1) & 0x1fff]
 #define next16()	(memory_[(program_counter_ + 1) & 0x1fff] | (memory_[(program_counter_ + 2) & 0x1fff] << 8))
 
-	printf("%04x\t%d %d\n", program_counter_ & 0x1fff, int(operation), int(addressing_mode));
+	printf("%04x\t%02x\t%d %d\t[x:%02x s:%02x]\n", program_counter_ & 0x1fff, memory_[program_counter_ & 0x1fff], int(operation), int(addressing_mode), x_, s_);
 
 	// Underlying assumption below: the instruction stream will never
 	// overlap with IO ports.
@@ -261,6 +261,9 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
 		case Operation::SET:	index_mode_ = true;				break;
 		case Operation::CLD:	decimal_mode_ = false;			break;
 		case Operation::SED:	decimal_mode_ = true;			break;
+		case Operation::CLC:	carry_flag_ = 0;				break;
+		case Operation::SEC:	carry_flag_ = 1;				break;
+		case Operation::CLV:	overflow_result_ = 0;			break;
 
 		case Operation::DEX:	--x_; set_nz(x_);				break;
 		case Operation::INX:	++x_; set_nz(x_);				break;
@@ -272,8 +275,9 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
 		case Operation::RTS: {
 			uint16_t target = pull();
 			target |= pull() << 8;
-			++target;
-			set_program_counter(target);
+			set_program_counter(target+1);
+			--program_counter_;				// To undo the unavoidable increment
+											// after exiting from here.
 		} break;
 
 		/*
diff --git a/InstructionSets/M50740/Executor.hpp b/InstructionSets/M50740/Executor.hpp
index 5c99623c5..404c41962 100644
--- a/InstructionSets/M50740/Executor.hpp
+++ b/InstructionSets/M50740/Executor.hpp
@@ -22,6 +22,12 @@ namespace M50740 {
 class Executor;
 using CachingExecutor = CachingExecutor<Executor, 0x1fff, 255, Instruction, false>;
 
+/*!
+	Executes M50740 code subject to heavy limitations:
+
+		* the instruction stream cannot run across any of the specialised IO addresses; and
+		* timing is correct to whole-opcode boundaries only.
+*/
 class Executor: public CachingExecutor {
 	public:
 		Executor();
@@ -115,6 +121,8 @@ class Executor: public CachingExecutor {
 		uint8_t negative_result_ = 0;
 		uint8_t zero_result_ = 0;
 		uint8_t interrupt_disable_ = 0;
+		uint8_t carry_flag_ = 0;
+		uint8_t overflow_result_;
 		bool index_mode_ = false;
 		bool decimal_mode_ = false;