From 8d87e9eb1ce6ee6d3b1c5bee58137e336b376555 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sun, 13 Oct 2019 21:32:34 -0400
Subject: [PATCH] The ACIA actually has two clocks, though on an ST they're
 both 500,000 Hz.

---
 Components/6850/6850.cpp     | 12 ++++++++----
 Components/6850/6850.hpp     | 19 ++++++++++++++++---
 Machines/AtariST/AtariST.cpp |  8 ++++----
 3 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/Components/6850/6850.cpp b/Components/6850/6850.cpp
index eb4e99c2b..01cd64296 100644
--- a/Components/6850/6850.cpp
+++ b/Components/6850/6850.cpp
@@ -13,9 +13,13 @@
 
 using namespace Motorola::ACIA;
 
-ACIA::ACIA(int clock_rate) {
-	transmit.set_writer_clock_rate(clock_rate);
-	request_to_send.set_writer_clock_rate(clock_rate);
+const HalfCycles ACIA::SameAsTransmit;
+
+ACIA::ACIA(HalfCycles transmit_clock_rate, HalfCycles receive_clock_rate) :
+	transmit_clock_rate_(transmit_clock_rate),
+	receive_clock_rate_((receive_clock_rate != SameAsTransmit) ? receive_clock_rate : transmit_clock_rate) {
+	transmit.set_writer_clock_rate(transmit_clock_rate.as_int());
+	request_to_send.set_writer_clock_rate(transmit_clock_rate.as_int());
 }
 
 uint8_t ACIA::read(int address) {
@@ -149,6 +153,6 @@ ClockingHint::Preference ACIA::preferred_clocking() {
 	return (transmit.write_data_time_remaining() > 0) ? ClockingHint::Preference::JustInTime : ClockingHint::Preference::None;
 }
 
-bool ACIA::get_interrupt_line() {
+bool ACIA::get_interrupt_line() const {
 	return interrupt_request_;
 }
diff --git a/Components/6850/6850.hpp b/Components/6850/6850.hpp
index a8ea3f96e..5111d5c89 100644
--- a/Components/6850/6850.hpp
+++ b/Components/6850/6850.hpp
@@ -19,7 +19,13 @@ namespace ACIA {
 
 class ACIA: public ClockingHint::Source {
 	public:
-		ACIA(int clock_rate);
+		static constexpr const HalfCycles SameAsTransmit = HalfCycles(0);
+
+		/*!
+			Constructs a new instance of ACIA which will receive a transmission clock at a rate of
+			@c transmit_clock_rate, and a receive clock at a rate of @c receive_clock_rate.
+		*/
+		ACIA(HalfCycles transmit_clock_rate, HalfCycles receive_clock_rate = SameAsTransmit);
 
 		/*!
 			Reads from the ACIA.
@@ -39,9 +45,13 @@ class ACIA: public ClockingHint::Source {
 		*/
 		void write(int address, uint8_t value);
 
-		void run_for(HalfCycles);
+		/*!
+			Advances @c transmission_cycles in time, which should be
+			counted relative to the @c transmit_clock_rate.
+		*/
+		void run_for(HalfCycles transmission_cycles);
 
-		bool get_interrupt_line();
+		bool get_interrupt_line() const;
 
 		// Input lines.
 		Serial::Line receive;
@@ -69,6 +79,9 @@ class ACIA: public ClockingHint::Source {
 		bool interrupt_request_ = false;
 
 		ClockingHint::Preference preferred_clocking() final;
+
+		HalfCycles transmit_clock_rate_;
+		HalfCycles receive_clock_rate_;
 };
 
 }
diff --git a/Machines/AtariST/AtariST.cpp b/Machines/AtariST/AtariST.cpp
index 5cff738c1..6277489ff 100644
--- a/Machines/AtariST/AtariST.cpp
+++ b/Machines/AtariST/AtariST.cpp
@@ -39,8 +39,8 @@ class ConcreteMachine:
 	public:
 		ConcreteMachine(const Target &target, const ROMMachine::ROMFetcher &rom_fetcher) :
 			mc68000_(*this),
-			keyboard_acia_(CLOCK_RATE / 10),
-			midi_acia_(CLOCK_RATE / 10),
+			keyboard_acia_(Cycles(500000)),
+			midi_acia_(Cycles(500000)),
 			ay_(audio_queue_),
 			speaker_(ay_) {
 			set_clock_rate(CLOCK_RATE);
@@ -372,8 +372,8 @@ class ConcreteMachine:
 		HalfCycles cycles_until_video_event_;
 
 		JustInTimeActor<Motorola::MFP68901::MFP68901> mfp_;
-		JustInTimeActor<Motorola::ACIA::ACIA, 10> keyboard_acia_;
-		JustInTimeActor<Motorola::ACIA::ACIA, 10> midi_acia_;
+		JustInTimeActor<Motorola::ACIA::ACIA, 16> keyboard_acia_;
+		JustInTimeActor<Motorola::ACIA::ACIA, 16> midi_acia_;
 
 		Concurrency::DeferringAsyncTaskQueue audio_queue_;
 		GI::AY38910::AY38910 ay_;