From e0736435f8e30622ce3c4d7caf14db8dd9a0aa4c Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 10 Apr 2021 12:00:53 -0400
Subject: [PATCH] Makes assumption that the address bus just holds its value
 during an internal operation.

---
 .../Clock SignalTests/Z80ContentionTests.mm   | 28 +++++++++----------
 .../Z80/Implementation/Z80Implementation.hpp  |  4 +++
 Processors/Z80/Implementation/Z80Storage.cpp  |  2 +-
 Processors/Z80/Implementation/Z80Storage.hpp  |  2 ++
 4 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/OSBindings/Mac/Clock SignalTests/Z80ContentionTests.mm b/OSBindings/Mac/Clock SignalTests/Z80ContentionTests.mm
index 4e2b3ea9f..712030334 100644
--- a/OSBindings/Mac/Clock SignalTests/Z80ContentionTests.mm	
+++ b/OSBindings/Mac/Clock SignalTests/Z80ContentionTests.mm	
@@ -388,13 +388,13 @@ struct ContentionCheck {
 
 		[self validate48Contention:{
 			{initial_pc, 4},
-			{initial_ir+1, 1},
-			{initial_ir+1, 1},
-			{initial_ir+1, 1},
-			{initial_ir+1, 1},
-			{initial_ir+1, 1},
-			{initial_ir+1, 1},
-			{initial_ir+1, 1},
+			{initial_ir, 1},
+			{initial_ir, 1},
+			{initial_ir, 1},
+			{initial_ir, 1},
+			{initial_ir, 1},
+			{initial_ir, 1},
+			{initial_ir, 1},
 		} z80:z80];
 		[self validatePlus3Contention:{{initial_pc, 11}} z80:z80];
 	}
@@ -414,13 +414,13 @@ struct ContentionCheck {
 		[self validate48Contention:{
 			{initial_pc, 4},
 			{initial_pc+1, 4},
-			{initial_ir+2, 1},
-			{initial_ir+2, 1},
-			{initial_ir+2, 1},
-			{initial_ir+2, 1},
-			{initial_ir+2, 1},
-			{initial_ir+2, 1},
-			{initial_ir+2, 1},
+			{initial_ir+1, 1},
+			{initial_ir+1, 1},
+			{initial_ir+1, 1},
+			{initial_ir+1, 1},
+			{initial_ir+1, 1},
+			{initial_ir+1, 1},
+			{initial_ir+1, 1},
 		} z80:z80];
 		[self validatePlus3Contention:{{initial_pc, 4}, {initial_pc+1, 11}} z80:z80];
 	}
diff --git a/Processors/Z80/Implementation/Z80Implementation.hpp b/Processors/Z80/Implementation/Z80Implementation.hpp
index 677d55d69..cbb4acc89 100644
--- a/Processors/Z80/Implementation/Z80Implementation.hpp
+++ b/Processors/Z80/Implementation/Z80Implementation.hpp
@@ -82,6 +82,10 @@ template <	class T,
 					}
 					number_of_cycles_ -= operation->machine_cycle.length;
 					last_request_status_ = request_status_;
+
+					// TODO: eliminate this conditional if all bus cycles have an address filled in.
+					last_address_bus_ = operation->machine_cycle.address ? *operation->machine_cycle.address : 0xdead;
+
 					number_of_cycles_ -= bus_handler_.perform_machine_cycle(operation->machine_cycle);
 					if(uses_bus_request && bus_request_line_) goto do_bus_acknowledge;
 				break;
diff --git a/Processors/Z80/Implementation/Z80Storage.cpp b/Processors/Z80/Implementation/Z80Storage.cpp
index b63c8392c..7aa1af49f 100644
--- a/Processors/Z80/Implementation/Z80Storage.cpp
+++ b/Processors/Z80/Implementation/Z80Storage.cpp
@@ -62,7 +62,7 @@ ProcessorStorage::ProcessorStorage() {
 
 #define Input(addr, val)				BusOp(InputStart(addr, val)), BusOp(InputWait(addr, val, false)), BusOp(InputWait(addr, val, true)), BusOp(InputEnd(addr, val))
 #define Output(addr, val)				BusOp(OutputStart(addr, val)), BusOp(OutputWait(addr, val, false)), BusOp(OutputWait(addr, val, true)), BusOp(OutputEnd(addr, val))
-#define InternalOperation(len)			{MicroOp::BusOperation, nullptr, nullptr, {PartialMachineCycle::Internal, HalfCycles(len), &ir_.full, nullptr, false}}
+#define InternalOperation(len)			{MicroOp::BusOperation, nullptr, nullptr, {PartialMachineCycle::Internal, HalfCycles(len), &last_address_bus_, nullptr, false}}
 
 /// A sequence is a series of micro-ops that ends in a move-to-next-program operation.
 #define Sequence(...)				{ __VA_ARGS__, {MicroOp::MoveToNextProgram} }
diff --git a/Processors/Z80/Implementation/Z80Storage.hpp b/Processors/Z80/Implementation/Z80Storage.hpp
index fb0f6bcdc..c682a259c 100644
--- a/Processors/Z80/Implementation/Z80Storage.hpp
+++ b/Processors/Z80/Implementation/Z80Storage.hpp
@@ -149,6 +149,8 @@ class ProcessorStorage {
 													// that knowledge of what the last opcode did is necessary to get bits 5 & 3
 													// correct for SCF and CCF.
 
+		uint16_t last_address_bus_ = 0;				// The value most recently put out on the address bus.
+
 		HalfCycles number_of_cycles_;
 
 		enum Interrupt: uint8_t {