Makes the TMS a sequence-point-generating JustInTimeActor.

ClockReceiver/ClockReceiver.hpp

@@ -10,7 +10,9 @@
 #define ClockReceiver_hpp
 
 #include "ForceInline.hpp"
+
 #include <cstdint>
+#include <limits>
 
 /*
 	Informal pattern for all classes that run from a clock cycle:
@@ -176,6 +178,9 @@ class Cycles: public WrappedInt<Cycles> {
 	public:
 		forceinline constexpr Cycles(IntType l) noexcept : WrappedInt<Cycles>(l) {}
 		forceinline constexpr Cycles() noexcept : WrappedInt<Cycles>() {}
+		forceinline static constexpr Cycles max() {
+			return Cycles(std::numeric_limits<IntType>::max());
+		}
 
 	private:
 		friend WrappedInt;
@@ -195,6 +200,9 @@ class HalfCycles: public WrappedInt<HalfCycles> {
 	public:
 		forceinline constexpr HalfCycles(IntType l) noexcept : WrappedInt<HalfCycles>(l) {}
 		forceinline constexpr HalfCycles() noexcept : WrappedInt<HalfCycles>() {}
+		forceinline static constexpr HalfCycles max() {
+			return HalfCycles(std::numeric_limits<IntType>::max());
+		}
 
 		forceinline constexpr HalfCycles(const Cycles &cycles) noexcept : WrappedInt<HalfCycles>(cycles.as_integral() * 2) {}
 

ClockReceiver/JustInTime.hpp

@@ -105,7 +105,9 @@ template <class T, class LocalTimeScale = HalfCycles, int multiplier = 1, int di
 			if constexpr (has_sequence_points<T>::value) {
 				time_until_event_ -= rhs;
 				if(time_until_event_ <= LocalTimeScale(0)) {
+					time_overrun_ = time_until_event_;
 					flush();
+					update_sequence_point();
 					return true;
 				}
 			}
@@ -174,6 +176,12 @@ template <class T, class LocalTimeScale = HalfCycles, int multiplier = 1, int di
 			return did_flush;
 		}
 
+		/// @returns a number in the range [-max, 0] indicating the offset of the most recent sequence
+		/// point from the final time at the end of the += that triggered the sequence point.
+		[[nodiscard]] forceinline LocalTimeScale last_sequence_point_overrun() {
+			return time_overrun_;
+		}
+
 		/// @returns the number of cycles until the next sequence-point-based flush, if the embedded object
 		/// supports sequence points; @c LocalTimeScale() otherwise.
 		[[nodiscard]] LocalTimeScale cycles_until_implicit_flush() const {
@@ -203,7 +211,7 @@ template <class T, class LocalTimeScale = HalfCycles, int multiplier = 1, int di
 
 	private:
 		T object_;
-		LocalTimeScale time_since_update_, time_until_event_;
+		LocalTimeScale time_since_update_, time_until_event_, time_overrun_;
 		bool is_flushed_ = true;
 		bool did_flush_ = false;
 

Components/9918/9918.cpp

@@ -708,9 +708,9 @@ HalfCycles Base::half_cycles_before_internal_cycles(int internal_cycles) {
 	return HalfCycles(((internal_cycles << 2) + (2 - cycles_error_)) / 3);
 }
 
-HalfCycles TMS9918::get_time_until_interrupt() {
+HalfCycles TMS9918::get_next_sequence_point() {
-	if(!generate_interrupts_ && !enable_line_interrupts_) return HalfCycles(-1);
+	if(!generate_interrupts_ && !enable_line_interrupts_) return HalfCycles::max();
-	if(get_interrupt_line()) return HalfCycles(0);
+	if(get_interrupt_line()) return HalfCycles::max();
 
 	// Calculate the amount of time until the next end-of-frame interrupt.
 	const int frame_length = 342 * mode_timing_.total_lines;

Components/9918/9918.hpp

@@ -75,13 +75,13 @@ class TMS9918: public Base {
 		void latch_horizontal_counter();
 
 		/*!
-			Returns the amount of time until @c get_interrupt_line would next return true if
+			Returns the amount of time until @c get_interrupt_line would next change if
 			there are no interceding calls to @c write or to @c read.
 
-			If get_interrupt_line is true now, returns zero. If get_interrupt_line would
+			If get_interrupt_line is true now of if get_interrupt_line would
-			never return true, returns -1.
+			never return true, returns HalfCycles::max().
 		*/
-		HalfCycles get_time_until_interrupt();
+		HalfCycles get_next_sequence_point();
 
 		/*!
 			Returns the amount of time until the nominated line interrupt position is

Machines/ColecoVision/ColecoVision.cpp

@@ -215,7 +215,9 @@ class ConcreteMachine:
 			}
 			const HalfCycles length = cycle.length + penalty;
 
-			vdp_ += length;
+			if(vdp_ += length) {
+				z80_.set_non_maskable_interrupt_line(vdp_->get_interrupt_line());
+			}
 			time_since_sn76489_update_ += length;
 
 			// Act only if necessary.
@@ -263,7 +265,6 @@ class ConcreteMachine:
 							case 5:
 								*cycle.value = vdp_->read(address);
 								z80_.set_non_maskable_interrupt_line(vdp_->get_interrupt_line());
-								time_until_interrupt_ = vdp_->get_time_until_interrupt();
 							break;
 
 							case 7: {
@@ -304,7 +305,6 @@ class ConcreteMachine:
 							case 5:
 								vdp_->write(address, *cycle.value);
 								z80_.set_non_maskable_interrupt_line(vdp_->get_interrupt_line());
-								time_until_interrupt_ = vdp_->get_time_until_interrupt();
 							break;
 
 							case 7:
@@ -341,13 +341,6 @@ class ConcreteMachine:
 				}
 			}
 
-			if(time_until_interrupt_ > 0) {
-				time_until_interrupt_ -= length;
-				if(time_until_interrupt_ <= HalfCycles(0)) {
-					z80_.set_non_maskable_interrupt_line(true, time_until_interrupt_);
-				}
-			}
-
 			return penalty;
 		}
 
@@ -408,7 +401,6 @@ class ConcreteMachine:
 		bool joysticks_in_keypad_mode_ = false;
 
 		HalfCycles time_since_sn76489_update_;
-		HalfCycles time_until_interrupt_;
 
 		Analyser::Dynamic::ConfidenceCounter confidence_counter_;
 		int pc_zero_accesses_ = 0;

Machines/MSX/MSX.cpp

@@ -419,7 +419,9 @@ class ConcreteMachine:
 			// but otherwise runs without pause.
 			const HalfCycles addition((cycle.operation == CPU::Z80::PartialMachineCycle::ReadOpcode) ? 2 : 0);
 			const HalfCycles total_length = addition + cycle.length;
-			vdp_ += total_length;
+			if(vdp_ += total_length) {
+				z80_.set_interrupt_line(vdp_->get_interrupt_line(), vdp_.last_sequence_point_overrun());
+			}
 			time_since_ay_update_ += total_length;
 			memory_slots_[0].cycles_since_update += total_length;
 			memory_slots_[1].cycles_since_update += total_length;
@@ -520,7 +522,6 @@ class ConcreteMachine:
 							case 0x98:	case 0x99:
 								*cycle.value = vdp_->read(address);
 								z80_.set_interrupt_line(vdp_->get_interrupt_line());
-								time_until_interrupt_ = vdp_->get_time_until_interrupt();
 							break;
 
 							case 0xa2:
@@ -545,7 +546,6 @@ class ConcreteMachine:
 							case 0x98:	case 0x99:
 								vdp_->write(address, *cycle.value);
 								z80_.set_interrupt_line(vdp_->get_interrupt_line());
-								time_until_interrupt_ = vdp_->get_time_until_interrupt();
 							break;
 
 							case 0xa0:	case 0xa1:
@@ -606,12 +606,6 @@ class ConcreteMachine:
 			if(!tape_player_is_sleeping_)
 				tape_player_.run_for(int(cycle.length.as_integral()));
 
-			if(time_until_interrupt_ > 0) {
-				time_until_interrupt_ -= total_length;
-				if(time_until_interrupt_ <= HalfCycles(0)) {
-					z80_.set_interrupt_line(true, time_until_interrupt_);
-				}
-			}
 			return addition;
 		}
 
@@ -785,7 +779,6 @@ class ConcreteMachine:
 		uint8_t unpopulated_[8192];
 
 		HalfCycles time_since_ay_update_;
-		HalfCycles time_until_interrupt_;
 
 		uint8_t key_states_[16];
 		int selected_key_line_ = 0;

Machines/MasterSystem/MasterSystem.cpp

@@ -214,7 +214,9 @@ class ConcreteMachine:
 		}
 
 		forceinline HalfCycles perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {
-			vdp_ += cycle.length;
+			if(vdp_ += cycle.length) {
+				z80_.set_interrupt_line(vdp_->get_interrupt_line(), vdp_.last_sequence_point_overrun());
+			}
 			time_since_sn76489_update_ += cycle.length;
 
 			if(cycle.is_terminal()) {
@@ -266,7 +268,6 @@ class ConcreteMachine:
 							case 0x80: case 0x81:
 								*cycle.value = vdp_->read(address);
 								z80_.set_interrupt_line(vdp_->get_interrupt_line());
-								time_until_interrupt_ = vdp_->get_time_until_interrupt();
 							break;
 							case 0xc0: {
 								if(memory_control_ & 0x4) {
@@ -330,7 +331,6 @@ class ConcreteMachine:
 							case 0x80: case 0x81:	// i.e. ports 0x80–0xbf.
 								vdp_->write(address, *cycle.value);
 								z80_.set_interrupt_line(vdp_->get_interrupt_line());
-								time_until_interrupt_ = vdp_->get_time_until_interrupt();
 							break;
 							case 0xc1: case 0xc0:	// i.e. ports 0xc0–0xff.
 								if(has_fm_audio_) {
@@ -374,13 +374,6 @@ class ConcreteMachine:
 				}
 			}
 
-			if(time_until_interrupt_ > 0) {
-				time_until_interrupt_ -= cycle.length;
-				if(time_until_interrupt_ <= HalfCycles(0)) {
-					z80_.set_interrupt_line(true, time_until_interrupt_);
-				}
-			}
-
 			// The pause button is debounced and takes effect only one line before pixels
 			// begin; time_until_debounce_ keeps track of the time until then.
 			time_until_debounce_ -= cycle.length;
@@ -505,7 +498,6 @@ class ConcreteMachine:
 		bool reset_is_pressed_ = false, pause_is_pressed_ = false;
 
 		HalfCycles time_since_sn76489_update_;
-		HalfCycles time_until_interrupt_;
 		HalfCycles time_until_debounce_;
 
 		uint8_t ram_[8*1024];