From 0fafbf50924366ecdd48b6bfeac04577ff81ae51 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 21 Jan 2021 19:08:38 -0500
Subject: [PATCH] Completes M50740 instruction set.

---
 InstructionSets/CachingExecutor.hpp |  7 +++++++
 InstructionSets/M50740/Executor.cpp | 21 +++++++++++++++++----
 InstructionSets/M50740/Executor.hpp |  1 +
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/InstructionSets/CachingExecutor.hpp b/InstructionSets/CachingExecutor.hpp
index ada7dffd7..c5fc80753 100644
--- a/InstructionSets/CachingExecutor.hpp
+++ b/InstructionSets/CachingExecutor.hpp
@@ -118,6 +118,13 @@ template <
 //			}
 		}
 
+		/*!
+			Indicates whether the processor is currently 'stopped', i.e. whether all attempts to run
+			should produce no activity. Some processors have such a state when waiting for
+			interrupts or for a reset.
+		*/
+		void set_is_stopped(bool) {}
+
 		/*!
 			Executes up to the next branch.
 		*/
diff --git a/InstructionSets/M50740/Executor.cpp b/InstructionSets/M50740/Executor.cpp
index a9e1d6de1..def6927e6 100644
--- a/InstructionSets/M50740/Executor.cpp
+++ b/InstructionSets/M50740/Executor.cpp
@@ -116,6 +116,15 @@ uint8_t Executor::flags() {
 		carry_flag_;
 }
 
+template<bool is_brk> inline void Executor::perform_interrupt() {
+	// BRK has an unused operand.
+	++program_counter_;
+	push(uint8_t(program_counter_ >> 8));
+	push(uint8_t(program_counter_ & 0xff));
+	push(flags() | (is_brk ? 0x10 : 0x00));
+	set_program_counter(uint16_t(memory_[0x1ff4] | (memory_[0x1ff5] << 8)));
+}
+
 template <Operation operation, AddressingMode addressing_mode> void Executor::perform() {
 	// Deal with all modes that don't access memory up here;
 	// those that access memory will go through a slightly longer
@@ -336,6 +345,14 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
 											// after exiting from here.
 		} break;
 
+		case Operation::BRK:
+			perform_interrupt<true>();
+			--program_counter_;				// To undo the unavoidable increment
+											// after exiting from here.
+		break;
+
+		case Operation::STP:	set_is_stopped(true);		break;
+
 		case Operation::COM:	set_nz(*operand ^= 0xff);	break;
 
 		case Operation::FST:	case Operation::SLW:	case Operation::NOP:
@@ -347,10 +364,6 @@ template <Operation operation> void Executor::perform(uint8_t *operand [[maybe_u
 		case Operation::PLA:	set_nz(a_ = pull());	break;
 		case Operation::PLP:	set_flags(pull());		break;
 
-		// TODO:
-		//
-		//	BRK, STP
-
 		case Operation::ASL:
 			carry_flag_ = *operand >> 7;
 			*operand <<= 1;
diff --git a/InstructionSets/M50740/Executor.hpp b/InstructionSets/M50740/Executor.hpp
index 1ab978fdd..744c4da43 100644
--- a/InstructionSets/M50740/Executor.hpp
+++ b/InstructionSets/M50740/Executor.hpp
@@ -132,6 +132,7 @@ class Executor: public CachingExecutor {
 		inline uint8_t pull();
 		inline void set_flags(uint8_t);
 		inline uint8_t flags();
+		template<bool is_brk> inline void perform_interrupt();
 };
 
 }