Merge pull request #102 from TomHarte/6532Accuracy

Improves 6532 counting accuracy

Components/6532/6532.hpp

@@ -51,7 +51,7 @@ template <class T> class MOS6532 {
 					if(address & 0x10)
 					{
 						timer_.writtenShift = timer_.activeShift = (decodedAddress - 0x04) * 3 + (decodedAddress / 0x07);	// i.e. 0, 3, 6, 10
-						timer_.value = ((unsigned int)(value) << timer_.activeShift) | ((1 << timer_.activeShift)-1);
+						timer_.value = ((unsigned int)value << timer_.activeShift) ;
 						timer_.interrupt_enabled = !!(address&0x08);
 						interrupt_status_ &= ~InterruptFlag::Timer;
 						evaluate_interrupts();
@@ -119,7 +119,7 @@ template <class T> class MOS6532 {
 				timer_.value -= number_of_cycles;
 			} else {
 				number_of_cycles -= timer_.value;
-				timer_.value = 0x100 - number_of_cycles;
+				timer_.value = (0x100 - number_of_cycles) & 0xff;
 				timer_.activeShift = 0;
 				interrupt_status_ |= InterruptFlag::Timer;
 				evaluate_interrupts();

Machines/Atari2600/Atari2600.cpp

@@ -22,6 +22,7 @@ Machine::Machine() :
 	tia_input_value_{0xff, 0xff},
 	cycles_since_speaker_update_(0),
 	cycles_since_video_update_(0),
+	cycles_since_6532_update_(0),
 	frame_record_pointer_(0),
 	is_ntsc_(true)
 {
@@ -62,6 +63,7 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 
 	cycles_since_speaker_update_ += cycles_run_for;
 	cycles_since_video_update_ += cycles_run_for;
+	cycles_since_6532_update_ += (cycles_run_for / 3);
 
 	if(operation != CPU6502::BusOperation::Ready) {
 
@@ -203,6 +205,7 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 
 		// check for a PIA access
 		if((address&0x1280) == 0x280) {
+			update_6532();
 			if(isReadOperation(operation)) {
 				returnValue &= mos6532_.get_register(address);
 			} else {
@@ -216,7 +219,6 @@ unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uin
 	}
 
 	if(!tia_->get_cycles_until_horizontal_blank(cycles_since_video_update_)) set_ready_line(false);
-	mos6532_.run_for_cycles(cycles_run_for / 3);
 
 	return cycles_run_for / 3;
 }
@@ -321,6 +323,12 @@ void Machine::update_video()
 	cycles_since_video_update_ = 0;
 }
 
+void Machine::update_6532()
+{
+	mos6532_.run_for_cycles(cycles_since_6532_update_);
+	cycles_since_6532_update_ = 0;
+}
+
 void Machine::synchronise()
 {
 	update_audio();

Machines/Atari2600/Atari2600.hpp

@@ -77,11 +77,15 @@ class Machine:
 
 		// speaker backlog accumlation counter
 		unsigned int cycles_since_speaker_update_;
-		void update_audio();
+		inline void update_audio();
 
 		// video backlog accumulation counter
 		unsigned int cycles_since_video_update_;
-		void update_video();
+		inline void update_video();
+
+		// RIOT backlog accumulation counter
+		unsigned int cycles_since_6532_update_;
+		inline void update_6532();
 
 		// output frame rate tracker
 		struct FrameRecord

OSBindings/Mac/Clock SignalTests/6532Tests.swift

@@ -21,14 +21,25 @@ class MOS6532Tests: XCTestCase {
 		with6532 {
 			// set a count of 128 at single-clock intervals
 			$0.setValue(128, forRegister:0x14)
+			XCTAssertEqual($0.value(forRegister: 4), 128)
 
-			// run for one clock and the count should now be 127
+			// run for one more clock and the count should now be 127
 			$0.run(forCycles: 1)
-			XCTAssert($0.value(forRegister: 4) == 127, "A single tick should decrease the counter once")
+			XCTAssertEqual($0.value(forRegister: 4), 127)
 
-			// run for a further 200 clock counts; timer should reach -73 = 183
+			// run for 127 clocks and the timer should be zero, but the timer flag will not yet be set
-			$0.run(forCycles: 200)
+			$0.run(forCycles: 127)
-			XCTAssert($0.value(forRegister: 4) == 183, "Timer should underflow and keep counting")
+			XCTAssertEqual($0.value(forRegister: 5) & 0x80, 0)
+			XCTAssertEqual($0.value(forRegister: 4), 0)
+
+			// after one more cycle the counter should be 255 and the timer flag will now be set
+			$0.run(forCycles: 1)
+			XCTAssertEqual($0.value(forRegister: 5) & 0x80, 0x80)
+			XCTAssertEqual($0.value(forRegister: 4), 255)
+
+			// run for a further 55 clock counts; timer should reach -200
+			$0.run(forCycles: 55)
+			XCTAssertEqual($0.value(forRegister: 4), 200)
 		}
 	}
 
@@ -37,26 +48,40 @@ class MOS6532Tests: XCTestCase {
 		with6532 {
 			// set a count of 28 at eight-clock intervals
 			$0.setValue(28, forRegister:0x15)
+			XCTAssertEqual($0.value(forRegister: 4), 28)
 
-			// run for seven clock and the count should still be 28
+			// one further cycle and the timer should hit 27
-			$0.run(forCycles: 7)
-			XCTAssert($0.value(forRegister: 4) == 28, "The timer should remain unchanged for seven clocks")
-
-			// run for a further clock and the count should now be 27
 			$0.run(forCycles: 1)
-			XCTAssert($0.value(forRegister: 4) == 27, "The timer should have decremented once after 8 cycles")
+			XCTAssertEqual($0.value(forRegister: 4), 27)
 
-			// run for a further 7 + 27*8 + 5 = 228 clock counts; timer should reach -5 = 0xfb
+			// run for seven clock and the count should still be 27
-			$0.run(forCycles: 228)
+			$0.run(forCycles: 7)
-			XCTAssert($0.value(forRegister: 4) == 0xfb, "Timer should underflow and start counting at single-clock pace")
+			XCTAssertEqual($0.value(forRegister: 4), 27)
+
+			// run for a further clock and the count should now be 26
+			$0.run(forCycles: 1)
+			XCTAssertEqual($0.value(forRegister: 4), 26)
+
+			// run for another 26 * 8 = 208 cycles and the count should hit zero without setting the timer flag, and
+			// stay there for seven more cycles
+			$0.run(forCycles: 208)
+			for _ in 0 ..< 8 {
+				XCTAssertEqual($0.value(forRegister: 5) & 0x80, 0)
+				XCTAssertEqual($0.value(forRegister: 4), 0)
+				$0.run(forCycles: 1)
+			}
+
+			// run six more, and the timer should reach 249, with the interrupt flag set
+			$0.run(forCycles: 6)
+			XCTAssertEqual($0.value(forRegister: 5) & 0x80, 0x80)
+			XCTAssertEqual($0.value(forRegister: 4), 249)
 
 			// timer should now resume dividing by eight
 			$0.run(forCycles: 7)
-			XCTAssert($0.value(forRegister: 4) == 0xfb, "Timer should remain unchanged for seven cycles")
+			XCTAssertEqual($0.value(forRegister: 4), 249)
 
-			// timer should now resume dividing by eight
 			$0.run(forCycles: 1)
-			XCTAssert($0.value(forRegister: 4) == 0xfa, "Timer should decrement after eighth cycle")
+			XCTAssertEqual($0.value(forRegister: 4), 248)
 		}
 	}
 
@@ -64,8 +89,6 @@ class MOS6532Tests: XCTestCase {
 		with6532 {
 			// set a count of 1 at single-clock intervals
 			$0.setValue(1, forRegister:0x1c)
-
-			// run for one clock and the count should now be zero
 			$0.run(forCycles: 1)
 
 			// interrupt shouldn't be signalled yet, bit should not be set