From b76104d14507bce0cf9e9dfdb99b0b907e43fdbb Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 14 Dec 2024 22:06:18 -0500
Subject: [PATCH] Start edging towards proper video timing.

---
 Machines/Commodore/Plus4/Interrupts.hpp | 15 ++++++++++-----
 Machines/Commodore/Plus4/Plus4.cpp      | 23 ++++++++++++++++++-----
 Machines/Commodore/Plus4/Video.hpp      | 10 ++++++++++
 3 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/Machines/Commodore/Plus4/Interrupts.hpp b/Machines/Commodore/Plus4/Interrupts.hpp
index 8cd50f483..a493a3449 100644
--- a/Machines/Commodore/Plus4/Interrupts.hpp
+++ b/Machines/Commodore/Plus4/Interrupts.hpp
@@ -12,13 +12,18 @@
 
 namespace Commodore::Plus4 {
 
+struct BusController {
+	virtual void set_irq_line(bool) = 0;
+	virtual void set_ready_line(bool) = 0;
+};
+
 struct Interrupts {
 public:
-	struct Delegate {
-		virtual void set_irq_line(bool) = 0;
-	};
+	Interrupts(BusController &delegate) : delegate_(delegate) {}
+	BusController &bus() {
+		return delegate_;
+	}
 
-	Interrupts(Delegate &delegate) : delegate_(delegate) {}
 
 	enum Flag {
 		Timer3 = 0x40,
@@ -59,7 +64,7 @@ private:
 		}
 	}
 
-	Delegate &delegate_;
+	BusController &delegate_;
 	uint8_t status_;
 	uint8_t mask_;
 	bool last_set_ = false;
diff --git a/Machines/Commodore/Plus4/Plus4.cpp b/Machines/Commodore/Plus4/Plus4.cpp
index d95cad805..bb5dfdf3a 100644
--- a/Machines/Commodore/Plus4/Plus4.cpp
+++ b/Machines/Commodore/Plus4/Plus4.cpp
@@ -99,8 +99,8 @@ private:
 };
 
 class ConcreteMachine:
+	public BusController,
 	public CPU::MOS6502::BusHandler,
-	public Interrupts::Delegate,
 	public MachineTypes::MappedKeyboardMachine,
 	public MachineTypes::TimedMachine,
 	public MachineTypes::ScanProducer,
@@ -148,16 +148,26 @@ public:
 		const auto length = video_.cycle_length(operation == CPU::MOS6502::BusOperation::Ready);
 
 		// Update other subsystems.
-		// TODO: timers decrement at a 894 KHz rate for NTSC television systems, 884 KHZ for PAL systems.
-		// Probably a function of the speed register?
 		timers_subcycles_ += length;
-		const auto timers_cycles = timers_subcycles_.divide(Cycles(5));
+		const auto timers_cycles = timers_subcycles_.divide(video_.timer_cycle_length());
 		timers_.tick(timers_cycles.as<int>());
 
 		video_.run_for(length);
 
 		// Perform actual access.
-		if(address < 0xfd00 || address >= 0xff40) {
+		if(address < 0x0002) {
+			// TODO: 0x0000: data directions for parallel IO; 1  = output.
+			// TODO: 0x0001:
+			//	b7 = serial data in;
+			//	b6 = serial clock in and cassette write;
+			//	b5 = [unconnected];
+			//	b4 = cassette read;
+			//	b3 = cassette motor, 1 = off;
+			//	b2 = serial ATN out;
+			//	b1 = serial clock out and cassette write;
+			//	b0 = serial data out.
+//			printf("%04x: %02x %c\n", address, *value, isReadOperation(operation) ? 'r' : 'w');
+		} else if(address < 0xfd00 || address >= 0xff40) {
 			if(isReadOperation(operation)) {
 				*value = map_.read(address);
 			} else {
@@ -277,6 +287,9 @@ private:
 	void set_irq_line(bool active) override {
 		m6502_.set_irq_line(active);
 	}
+	void set_ready_line(bool active) override {
+		m6502_.set_ready_line(active);
+	}
 
 	void page_rom() {
 		// TODO: allow other ROM selection. And no ROM?
diff --git a/Machines/Commodore/Plus4/Video.hpp b/Machines/Commodore/Plus4/Video.hpp
index 37f851467..5a4b32291 100644
--- a/Machines/Commodore/Plus4/Video.hpp
+++ b/Machines/Commodore/Plus4/Video.hpp
@@ -127,6 +127,10 @@ public:
 		}
 	}
 
+	Cycles timer_cycle_length() const {
+		return is_ntsc_ ? Cycles(16) : Cycles(20);
+	}
+
 	// Outer clock is [NTSC or PAL] colour subcarrier * 2.
 	//
 	// 65 cycles = 64µs?
@@ -400,6 +404,12 @@ private:
 		50,		96,		32,		9,
 		5,		41,
 	};
+
+	enum class FetchPhase {
+		Waiting,
+		FetchingCharacters,
+		FetchingAttributs,
+	} fetch_phase_ = FetchPhase::Waiting;
 };
 
 }