From 033655835a47f16bc2a0d275fef3f3f6df84c264 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 13 Aug 2015 18:59:23 +0100
Subject: [PATCH] My understanding now is that object position counting will
 begin the cycle after the call is made, not that cycle, and that the timer
 loops just once, with the logic for counter pumping being whether the
 relevant flag is still set, irregardless of whether the counter is still
 going.

---
 Machines/Atari2600.cpp | 31 +++++++++++++++++++++++--------
 Machines/Atari2600.hpp |  4 +++-
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/Machines/Atari2600.cpp b/Machines/Atari2600.cpp
index 66812210c..dddfde2c7 100644
--- a/Machines/Atari2600.cpp
+++ b/Machines/Atari2600.cpp
@@ -24,6 +24,7 @@ Machine::Machine()
 	_piaTimerStatus = 0xff;
 	memset(_collisions, 0xff, sizeof(_collisions));
 	_rom = nullptr;
+	_hMoveWillCount = false;
 
 	setup6502();
 	set_reset_line(true);
@@ -163,21 +164,25 @@ void Machine::output_pixels(int count)
 	const int32_t start_of_sync = 214;
 	const int32_t end_of_sync = 198;
 
-	_timestamp += count;
 	while(count--)
 	{
 		OutputState state;
 
 		// update hmove
-		if (!(_horizontalTimer&3) && _hMoveFlags) {
+		if (!(_horizontalTimer&3)) {
+
+			const uint8_t counterValue = _hMoveCounter ^ 0x7;
 			for(int c = 0; c < 5; c++) {
-				if ((_hMoveCounter^8^(_objectMotion[c] >> 4)) == 0xf)
+				if (counterValue == (_objectMotion[c] >> 4))
 					_hMoveFlags &= ~(1 << c);
 				if (_hMoveFlags&(1 << c))
 					_objectCounter[c] = (_objectCounter[c]+1)%160;
 			}
 
-			_hMoveCounter = (_hMoveCounter-1)&0xf;
+			if(_hMoveIsCounting) {
+				_hMoveIsCounting = !!_hMoveCounter;
+				_hMoveCounter = (_hMoveCounter-1)&0xf;
+			}
 		}
 
 		// logic: if in vsync, output that; otherwise if in vblank then output that;
@@ -245,6 +250,8 @@ void Machine::output_pixels(int count)
 		_horizontalTimer--;
 		const int32_t sign_extension = _horizontalTimer >> 31;
 		_horizontalTimer = (_horizontalTimer&~sign_extension) | (sign_extension&horizontalTimerReload);
+
+		_timestamp ++;
 	}
 }
 
@@ -254,7 +261,7 @@ int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t add
 
 	uint8_t returnValue = 0xff;
 	int cycles_run_for = 1;
-	const int32_t ready_line_disable_time = 225;//horizontalTimerReload;
+	const int32_t ready_line_disable_time = 227;//horizontalTimerReload;
 
 	if(operation == CPU6502::BusOperation::Ready) {
 		int32_t distance_to_end_of_ready = (_horizontalTimer - ready_line_disable_time + horizontalTimerReload + 1)%(horizontalTimerReload + 1);
@@ -264,6 +271,13 @@ int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t add
 		output_pixels(3);
 	}
 
+	if(_hMoveWillCount) {
+		_hMoveCounter = 0x0f;
+		_hMoveFlags = 0x1f;
+		_hMoveIsCounting = true;
+		_hMoveWillCount = false;
+	}
+
 	if(_horizontalTimer == ready_line_disable_time)
 		set_ready_line(false);
 
@@ -387,7 +401,9 @@ int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t add
 					case 0x21:
 					case 0x22:
 					case 0x23:
-					case 0x24: _objectMotion[decodedAddress - 0x20] = *value;	break;
+					case 0x24:
+						_objectMotion[decodedAddress - 0x20] = *value;
+					break;
 
 					case 0x25: _playerGraphicsLatchEnable[0] = *value;	break;
 					case 0x26: _playerGraphicsLatchEnable[1] = *value;	break;
@@ -402,8 +418,7 @@ int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t add
 
 					case 0x2a:
 						_vBlankExtend = true;
-						_hMoveCounter = 15;
-						_hMoveFlags = 0x1f;
+						_hMoveWillCount = true;
 					break;
 					case 0x2b:
 						_objectMotion[0] =
diff --git a/Machines/Atari2600.hpp b/Machines/Atari2600.hpp
index 9a3d9dabb..d66b3604b 100644
--- a/Machines/Atari2600.hpp
+++ b/Machines/Atari2600.hpp
@@ -66,8 +66,10 @@ class Machine: public CPU6502::Processor<Machine> {
 		int32_t _horizontalTimer;
 		bool _vSyncEnabled, _vBlankEnabled;
 		bool _vBlankExtend;
-		uint8_t _hMoveCounter, _hMoveFlags;
+		uint8_t _hMoveCounter;
+		bool _hMoveIsCounting, _hMoveWillCount;
 		uint8_t _objectCounter[5], _objectMotion[5];
+		uint8_t _hMoveFlags;
 
 		// collisions
 		uint8_t _collisions[8];