From 516d78f5a890c99815335ef0171301555bf59eef Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 12 Oct 2019 23:46:57 -0400
Subject: [PATCH] Attempts to implement transmission interrupts and
 ClockingHint::Source.

---
 Components/6850/6850.cpp | 32 +++++++++++++++++++++++++-------
 Components/6850/6850.hpp |  9 ++++++++-
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/Components/6850/6850.cpp b/Components/6850/6850.cpp
index f86989c5d..e935590ff 100644
--- a/Components/6850/6850.cpp
+++ b/Components/6850/6850.cpp
@@ -18,12 +18,14 @@ ACIA::ACIA() {}
 uint8_t ACIA::read(int address) {
 	if(address&1) {
 		LOG("Read from receive register");
+		interrupt_request_ = false;
 	} else {
 		LOG("Read status");
 		return
 			((next_transmission_ == NoTransmission) ? 0x02 : 0x00) |
 			(data_carrier_detect.read() ? 0x04 : 0x00) |
-			(clear_to_send.read() ? 0x08 : 0x00)
+			(clear_to_send.read() ? 0x08 : 0x00) |
+			(interrupt_request_ ? 0x80 : 0x00)
 		;
 
 		// b0: receive data full.
@@ -42,6 +44,8 @@ void ACIA::write(int address, uint8_t value) {
 	if(address&1) {
 		next_transmission_ = value;
 		consider_transmission();
+		update_clocking_observer();
+		interrupt_request_ = false;
 	} else {
 		if((value&3) == 3) {
 			transmit.reset_writing();
@@ -82,16 +86,22 @@ void ACIA::write(int address, uint8_t value) {
 
 void ACIA::run_for(HalfCycles length) {
 	// Transmission.
-	int transmit_advance = length.as_int();
-	if(next_transmission_ != NoTransmission) {
-		const auto write_data_time_remaining = transmit.write_data_time_remaining();
-		if(transmit_advance > write_data_time_remaining) {
+	const int transmit_advance = length.as_int();
+	const auto write_data_time_remaining = transmit.write_data_time_remaining();
+
+	if(transmit_advance > write_data_time_remaining) {
+		if(next_transmission_ != NoTransmission) {
 			transmit.flush_writing();
-			transmit_advance -= write_data_time_remaining;
 			consider_transmission();
+			transmit.advance_writer(transmit_advance - write_data_time_remaining);
+		} else {
+			transmit.advance_writer(transmit_advance);
+			update_clocking_observer();
+			interrupt_request_ |= transmit_interrupt_enabled_;
 		}
+	} else {
+		transmit.advance_writer(transmit_advance);
 	}
-	transmit.advance_writer(transmit_advance);
 
 	// Reception.
 }
@@ -129,3 +139,11 @@ void ACIA::consider_transmission() {
 		next_transmission_ = NoTransmission;
 	}
 }
+
+ClockingHint::Preference ACIA::preferred_clocking() {
+	return (transmit.write_data_time_remaining() > 0) ? ClockingHint::Preference::JustInTime : ClockingHint::Preference::None;
+}
+
+bool ACIA::get_interrupt_line() {
+	return interrupt_request_;
+}
diff --git a/Components/6850/6850.hpp b/Components/6850/6850.hpp
index bb7aec9c2..1b76726a9 100644
--- a/Components/6850/6850.hpp
+++ b/Components/6850/6850.hpp
@@ -11,12 +11,13 @@
 
 #include <cstdint>
 #include "../../ClockReceiver/ClockReceiver.hpp"
+#include "../../ClockReceiver/ClockingHintSource.hpp"
 #include "../SerialPort/SerialPort.hpp"
 
 namespace Motorola {
 namespace ACIA {
 
-class ACIA {
+class ACIA: public ClockingHint::Source {
 	public:
 		ACIA();
 
@@ -40,6 +41,8 @@ class ACIA {
 
 		void run_for(HalfCycles);
 
+		bool get_interrupt_line();
+
 		// Input lines.
 		Serial::Line receive;
 		Serial::Line clear_to_send;
@@ -62,6 +65,10 @@ class ACIA {
 
 		bool receive_interrupt_enabled_ = false;
 		bool transmit_interrupt_enabled_ = false;
+
+		bool interrupt_request_ = false;
+
+		ClockingHint::Preference preferred_clocking() final;
 };
 
 }