From b4ec9d70da01b6e49a3b2e77f8611614be711a92 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Tue, 3 Aug 2021 22:19:41 -0400
Subject: [PATCH] Adds the CNT input.

---
 Components/6526/6526.hpp                      |  3 +++
 .../Implementation/6526Implementation.hpp     | 12 +++++++--
 .../6526/Implementation/6526Storage.hpp       | 25 ++++++++++---------
 .../WolfgangLorenzTests.swift                 |  2 --
 4 files changed, 26 insertions(+), 16 deletions(-)

diff --git a/Components/6526/6526.hpp b/Components/6526/6526.hpp
index 6d5fc1b5d..3af90d700 100644
--- a/Components/6526/6526.hpp
+++ b/Components/6526/6526.hpp
@@ -60,6 +60,9 @@ template <typename PortHandlerT, Personality personality> class MOS6526:
 		/// @returns @c true if the interrupt output is active, @c false otherwise.
 		bool get_interrupt_line();
 
+		/// Sets the current state of the CNT input.
+		void set_cnt_input(bool active);
+
 	private:
 		PortHandlerT &port_handler_;
 		TODStorage<personality == Personality::P8250> tod_;
diff --git a/Components/6526/Implementation/6526Implementation.hpp b/Components/6526/Implementation/6526Implementation.hpp
index bd507f72a..dabdbf353 100644
--- a/Components/6526/Implementation/6526Implementation.hpp
+++ b/Components/6526/Implementation/6526Implementation.hpp
@@ -48,6 +48,12 @@ bool MOS6526<BusHandlerT, personality>::get_interrupt_line() {
 	return interrupt_state_ & 0x80;
 }
 
+template <typename BusHandlerT, Personality personality>
+void MOS6526<BusHandlerT, personality>::set_cnt_input(bool active) {
+	cnt_edge_ = active && !cnt_state_;
+	cnt_state_ = active;
+}
+
 template <typename BusHandlerT, Personality personality>
 void MOS6526<BusHandlerT, personality>::write(int address, uint8_t value) {
 	address &= 0xf;
@@ -166,11 +172,13 @@ void MOS6526<BusHandlerT, personality>::run_for(const HalfCycles half_cycles) {
 		pending_ &= PendingClearMask;
 
 		// TODO: use CNT potentially to clock timer A, elimiante conditional above.
-		const bool timer1_did_reload = counter_[0].template advance<false>(false);
+		const bool timer1_did_reload = counter_[0].template advance<false>(false, cnt_state_, cnt_edge_);
 
 		const bool timer1_carry = timer1_did_reload && (counter_[1].control & 0x60) == 0x40;
-		const bool timer2_did_reload = counter_[1].template advance<true>(timer1_carry);
+		const bool timer2_did_reload = counter_[1].template advance<true>(timer1_carry, cnt_state_, cnt_edge_);
 		posit_interrupt((timer1_did_reload ? 0x01 : 0x00) | (timer2_did_reload ? 0x02 : 0x00));
+
+		cnt_edge_ = false;
 	}
 }
 
diff --git a/Components/6526/Implementation/6526Storage.hpp b/Components/6526/Implementation/6526Storage.hpp
index c5bd1f08b..4fd369d6d 100644
--- a/Components/6526/Implementation/6526Storage.hpp
+++ b/Components/6526/Implementation/6526Storage.hpp
@@ -174,6 +174,8 @@ template <> class TODStorage<true>: public TODBase {
 };
 
 struct MOS6526Storage {
+	bool cnt_state_ = false;	// Inactive by default.
+	bool cnt_edge_ = false;
 	HalfCycles half_divider_;
 
 	uint8_t output_[2] = {0, 0};
@@ -206,7 +208,7 @@ struct MOS6526Storage {
 			control = v;
 		}
 
-		template <bool is_counter_2> bool advance(bool chained_input) {
+		template <bool is_counter_2> bool advance(bool chained_input, bool cnt_state, bool cnt_edge) {
 			// TODO: remove most of the conditionals here in favour of bit shuffling.
 
 			pending = (pending & PendingClearMask) << 1;
@@ -222,27 +224,31 @@ struct MOS6526Storage {
 				control &= ~0x10;
 			}
 
+			// Keep a history of the one-shot bit.
+			if(control & 0x08) {
+				pending |= OneShotInOne;
+			}
+
 			// Determine whether an input clock is applicable.
 			if constexpr(is_counter_2) {
 				switch(control&0x60) {
 					case 0x00:	// Count Phi2 pulses.
 						pending |= TestInputNow;
 					break;
+					case 0x20:	// Count negative CNTs, with an extra cycle of delay.
+						pending |= cnt_edge ? TestInputInOne : 0;
+					break;
 					case 0x40:	// Count timer A reloads.
 						pending |= chained_input ? TestInputNow : 0;
 					break;
-
-					case 0x20:	// Count negative CNTs.
 					case 0x60:	// Count timer A transitions when CNT is low.
-					default:
-						// TODO: all other forms of input.
-						assert(false);
+						pending |= chained_input && cnt_edge ? TestInputNow : 0;
 					break;
 				}
 			} else {
 				if(!(control&0x20)) {
 					pending |= TestInputNow;
-				} else if (chained_input) {	// TODO: check CNT directly, probably?
+				} else if (cnt_edge) {
 					pending |= TestInputInOne;
 				}
 			}
@@ -250,11 +256,6 @@ struct MOS6526Storage {
 				pending |= ApplyClockInTwo;
 			}
 
-			// Keep a history of the one-shot bit.
-			if(control & 0x08) {
-				pending |= OneShotInOne | OneShotNow;
-			}
-
 
 			//
 			// Perform a timer tick and decide whether a reload is prompted.
diff --git a/OSBindings/Mac/Clock SignalTests/WolfgangLorenzTests.swift b/OSBindings/Mac/Clock SignalTests/WolfgangLorenzTests.swift
index c982e00fc..b89bf83b3 100644
--- a/OSBindings/Mac/Clock SignalTests/WolfgangLorenzTests.swift	
+++ b/OSBindings/Mac/Clock SignalTests/WolfgangLorenzTests.swift	
@@ -288,7 +288,6 @@ class WolfgangLorenzTests: XCTestCase, CSTestMachineTrapHandler {
 	}
 
 	func testCIALoadTH() {
-		// TODO: Uses one of the CNT input modes of timer B.
 		runTest("loadth", suffixes: [""], processor: .processor6502)
 	}
 
@@ -313,7 +312,6 @@ class WolfgangLorenzTests: XCTestCase, CSTestMachineTrapHandler {
 	}
 
 	func testCIACNTDefault() {
-		// TODO: Uses one of the CNT input modes of timer B.
 		runTest("cntdef", suffixes: [""], processor: .processor6502)
 	}