diff --git a/Components/9918/9918.cpp b/Components/9918/9918.cpp
index 2c02748a1..84f24d6ec 100644
--- a/Components/9918/9918.cpp
+++ b/Components/9918/9918.cpp
@@ -66,11 +66,15 @@ void TMS9918::run_for(const HalfCycles cycles) {
 	// PAL output is 313 lines total. NTSC output is 262 lines total.
 	// Interrupt is signalled upon entering the lower border.
 
+	// Keep a count of cycles separate from internal counts to avoid
+	// potential errors mapping back and forth.
+	half_cycles_into_frame_ = (half_cycles_into_frame_ + cycles) % HalfCycles(frame_lines_ * 228 * 2);
+
 	// Convert to 342 cycles per line; the internal clock is 1.5 times the
 	// nominal 3.579545 Mhz that I've advertised for this part.
 	int int_cycles = (cycles.as_int() * 3) + cycles_error_;
-	cycles_error_ = int_cycles & 3;
-	int_cycles >>= 2;
+	cycles_error_ = int_cycles & 7;
+	int_cycles >>= 3;
 	if(!int_cycles) return;
 
 	//
@@ -296,3 +300,16 @@ uint8_t TMS9918::get_register(int address) {
 void TMS9918::reevaluate_interrupts() {
 	
 }
+
+HalfCycles TMS9918::get_time_until_interrupt() {
+	if(!generate_interrupts_) return HalfCycles(-1);
+	if(get_interrupt_line()) return HalfCycles(-1);
+
+	const int half_cycles_per_frame = frame_lines_ * 228 * 2;
+	int half_cycles_remaining = (192 * 228 * 2 + half_cycles_per_frame - half_cycles_into_frame_.as_int()) % half_cycles_per_frame;
+	return HalfCycles(half_cycles_remaining);
+}
+
+bool TMS9918::get_interrupt_line() {
+	return (status_ & 0x80) && generate_interrupts_;
+}
diff --git a/Components/9918/9918.hpp b/Components/9918/9918.hpp
index 3bed97931..fc8c2b1e5 100644
--- a/Components/9918/9918.hpp
+++ b/Components/9918/9918.hpp
@@ -44,6 +44,9 @@ class TMS9918 {
 		void set_register(int address, uint8_t value);
 		uint8_t get_register(int address);
 
+		HalfCycles get_time_until_interrupt();
+		bool get_interrupt_line();
+
 	private:
 		std::shared_ptr<Outputs::CRT::CRT> crt_;
 	
@@ -73,6 +76,7 @@ class TMS9918 {
 
 		void reevaluate_interrupts();
 
+		HalfCycles half_cycles_into_frame_;
 		int column_ = 0, row_ = 0, output_column_ = 0;
 		int cycles_error_ = 0;
 		uint32_t *pixel_target_ = nullptr;
@@ -93,7 +97,7 @@ class TMS9918 {
 		uint8_t pattern_buffer_[40];
 		uint8_t colour_buffer_[32];
 		int access_pointer_ = 0;
-		uint8_t pattern_name_;
+		uint8_t pattern_name_ = 0;
 };
 
 };
diff --git a/Machines/MSX/MSX.cpp b/Machines/MSX/MSX.cpp
index c395c84f7..f50af639c 100644
--- a/Machines/MSX/MSX.cpp
+++ b/Machines/MSX/MSX.cpp
@@ -20,7 +20,15 @@
 
 namespace MSX {
 
-class AYPortHandler: public GI::AY38910::PortHandler {
+struct AYPortHandler: public GI::AY38910::PortHandler {
+	void set_port_output(bool port_b, uint8_t value) {
+		printf("AY port %c output: %02x\n", port_b ? 'b' : 'a', value);
+	}
+
+	uint8_t get_port_input(bool port_b) {
+		printf("AY port %c input\n", port_b ? 'b' : 'a');
+		return 0xff;
+	}
 };
 
 class ConcreteMachine:
@@ -65,6 +73,7 @@ class ConcreteMachine:
 		}
 
 		void page_memory(uint8_t value) {
+			printf("Page %02x\n", value);
 			for(int c = 0; c < 4; ++c) {
 				read_pointers_[c] = unpopulated_;
 				write_pointers_[c] = scratch_;
@@ -87,6 +96,13 @@ class ConcreteMachine:
 		}
 
 		HalfCycles perform_machine_cycle(const CPU::Z80::PartialMachineCycle &cycle) {
+			if(time_until_interrupt_ > 0) {
+				time_until_interrupt_ -= cycle.length;
+				if(time_until_interrupt_ <= HalfCycles(0)) {
+					z80_.set_interrupt_line(true, time_until_interrupt_);
+				}
+			}
+
 			uint16_t address = cycle.address ? *cycle.address : 0x0000;
 			switch(cycle.operation) {
 				case CPU::Z80::PartialMachineCycle::ReadOpcode:
@@ -104,6 +120,8 @@ class ConcreteMachine:
 							vdp_->run_for(time_since_vdp_update_);
 							time_since_vdp_update_ = 0;
 							*cycle.value = vdp_->get_register(address);
+							z80_.set_interrupt_line(vdp_->get_interrupt_line());
+							time_until_interrupt_ = vdp_->get_time_until_interrupt();
 						break;
 
 						case 0xa2:
@@ -124,6 +142,8 @@ class ConcreteMachine:
 							vdp_->run_for(time_since_vdp_update_);
 							time_since_vdp_update_ = 0;
 							vdp_->set_register(address, *cycle.value);
+							z80_.set_interrupt_line(vdp_->get_interrupt_line());
+							time_until_interrupt_ = vdp_->get_time_until_interrupt();
 						break;
 
 						case 0xa0:
@@ -205,7 +225,7 @@ class ConcreteMachine:
 				uint8_t get_value(int port) {
 					if(port == 1) {
 						printf("?? Read keyboard\n");
-					}
+					} else printf("What what?\n");
 					return 0xff;
 				}
 
@@ -229,6 +249,7 @@ class ConcreteMachine:
 		std::vector<uint8_t> basic_, main_;
 
 		HalfCycles time_since_vdp_update_;
+		HalfCycles time_until_interrupt_;
 };
 
 }