Merge pull request #562 from TomHarte/TimingTweaks

Corrects residual Master System interrupt timing issues.

Components/9918/9918.cpp

@@ -66,7 +66,7 @@ Base::Base(Personality p) :
 	}
 
 	if(is_sega_vdp(personality_)) {
-		mode_timing_.line_interrupt_position = 65;
+		mode_timing_.line_interrupt_position = 64;
 
 		mode_timing_.end_of_frame_interrupt_position.column = 63;
 		mode_timing_.end_of_frame_interrupt_position.row = 193;
@@ -564,7 +564,7 @@ void TMS9918::set_register(int address, uint8_t value) {
 
 uint8_t TMS9918::get_current_line() {
 	// Determine the row to return.
-	static const int row_change_position = 62;	// This is the proper Master System value; substitute if any other VDPs turn out to have this functionality.
+	static const int row_change_position = 63;	// This is the proper Master System value; substitute if any other VDPs turn out to have this functionality.
 	int source_row =
 		(write_pointer_.column < row_change_position)
 			? (write_pointer_.row + mode_timing_.total_lines - 1)%mode_timing_.total_lines
@@ -638,23 +638,31 @@ HalfCycles TMS9918::get_time_until_interrupt() {
 
 	// Calculate the amount of time until the next end-of-frame interrupt.
 	const int frame_length = 342 * mode_timing_.total_lines;
-	const int time_until_frame_interrupt =
+	int time_until_frame_interrupt =
 		(
 			((mode_timing_.end_of_frame_interrupt_position.row * 342) + mode_timing_.end_of_frame_interrupt_position.column + frame_length) -
 			((write_pointer_.row * 342) + write_pointer_.column)
 		) % frame_length;
+	if(!time_until_frame_interrupt) time_until_frame_interrupt = frame_length;
 
 	if(!enable_line_interrupts_) return half_cycles_before_internal_cycles(time_until_frame_interrupt);
 
-	// Calculate the row upon which the next line interrupt will occur.
+	// Calculate when the next line interrupt will occur.
 	int next_line_interrupt_row = -1;
 
+	int cycles_to_next_interrupt_threshold = mode_timing_.line_interrupt_position - write_pointer_.column;
+	int line_of_next_interrupt_threshold = write_pointer_.row;
+	if(cycles_to_next_interrupt_threshold <= 0) {
+		cycles_to_next_interrupt_threshold += 342;
+		++line_of_next_interrupt_threshold;
+	}
+
 	if(is_sega_vdp(personality_)) {
 		// If there is still time for a line interrupt this frame, that'll be it;
 		// otherwise it'll be on the next frame, supposing there's ever time for
 		// it at all.
-		if(write_pointer_.row+line_interrupt_counter <= mode_timing_.pixel_lines) {
+		if(line_of_next_interrupt_threshold + line_interrupt_counter <= mode_timing_.pixel_lines) {
-			next_line_interrupt_row = write_pointer_.row+line_interrupt_counter;
+			next_line_interrupt_row = line_of_next_interrupt_threshold + line_interrupt_counter;
 		} else {
 			if(line_interrupt_target <= mode_timing_.pixel_lines)
 				next_line_interrupt_row = mode_timing_.total_lines + line_interrupt_target;
@@ -671,10 +679,7 @@ HalfCycles TMS9918::get_time_until_interrupt() {
 
 	// Figure out the number of internal cycles until the next line interrupt, which is the amount
 	// of time to the next tick over and then next_line_interrupt_row - row_ lines further.
-	int local_cycles_until_next_tick = (mode_timing_.line_interrupt_position - write_pointer_.column + 342) % 342;
+	const int local_cycles_until_line_interrupt = cycles_to_next_interrupt_threshold + (next_line_interrupt_row - line_of_next_interrupt_threshold) * 342;
-	if(!local_cycles_until_next_tick) local_cycles_until_next_tick += 342;
-	const int local_cycles_until_line_interrupt = local_cycles_until_next_tick + (next_line_interrupt_row - write_pointer_.row) * 342;
-
 	if(!generate_interrupts_) return half_cycles_before_internal_cycles(local_cycles_until_line_interrupt);
 
 	// Return whichever interrupt is closer.
@@ -687,9 +692,6 @@ bool TMS9918::get_interrupt_line() {
 
 // MARK: -
 
-//										if(sprite.shift_position > 0 && !sprites_magnified_)
-//											sprite.shift_position *= 2;
-
 void Base::draw_tms_character(int start, int end) {
 	LineBuffer &line_buffer = line_buffers_[read_pointer_.row];
 

OSBindings/Mac/Clock SignalTests/MasterSystemVDPTests.mm

@@ -116,4 +116,45 @@
 	NSAssert(vdp.get_interrupt_line(), @"Interrupt line wasn't set when promised");
 }
 
+- (void)testPrediction {
+	TI::TMS::TMS9918 vdp(TI::TMS::Personality::SMSVDP);
+
+	for(int c = 0; c < 256; ++c) {
+		for(int with_eof = (c < 192) ? 0 : 1; with_eof < 2; ++with_eof) {
+			// Enable or disable end-of-frame interrupts as required.
+			vdp.set_register(1, with_eof ? 0x20 : 0x00);
+			vdp.set_register(1, 0x81);
+
+			// Enable line interrupts.
+			vdp.set_register(1, 0x10);
+			vdp.set_register(1, 0x80);
+
+			// Set the line interrupt timing as desired.
+			vdp.set_register(1, c);
+			vdp.set_register(1, 0x8a);
+
+			// Now run through an entire frame...
+			int half_cycles = 262*224*2;
+			int last_time_until_interrupt = vdp.get_time_until_interrupt().as_int();
+			while(half_cycles--) {
+				// Validate that an interrupt happened if one was expected, and clear anything that's present.
+				NSAssert(vdp.get_interrupt_line() == (last_time_until_interrupt == 0), @"Unexpected interrupt state change; expected %d but got %d; position %d %d @ %d", (last_time_until_interrupt == 0), vdp.get_interrupt_line(), c, with_eof, half_cycles);
+				vdp.get_register(1);
+
+				vdp.run_for(HalfCycles(1));
+
+				// Get the time until interrupt.
+				int time_until_interrupt = vdp.get_time_until_interrupt().as_int();
+				NSAssert(time_until_interrupt != -1, @"No interrupt scheduled; position %d %d @ %d", c, with_eof, half_cycles);
+				NSAssert(time_until_interrupt >= 0, @"Interrupt is scheduled in the past; position %d %d @ %d", c, with_eof, half_cycles);
+
+				if(last_time_until_interrupt) {
+					NSAssert(time_until_interrupt == (last_time_until_interrupt - 1), @"Discontinuity found in interrupt prediction; from %d to %d; position %d %d @ %d", last_time_until_interrupt, time_until_interrupt, c, with_eof, half_cycles);
+				}
+				last_time_until_interrupt = time_until_interrupt;
+			}
+		}
+	}
+}
+
 @end