Adds an IWM shim and corrects graphics output.

... now that there is some.

Components/DiskII/IWM.cpp

@@ -0,0 +1,67 @@
+//
+//  IWM.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 05/05/2019.
+//  Copyright © 2019 Thomas Harte. All rights reserved.
+//
+
+#include "IWM.hpp"
+
+using namespace Apple;
+
+IWM::IWM(int clock_rate) {
+
+}
+
+uint8_t IWM::read(int address) {
+	access(address);
+
+	switch(q_switches_) {
+		default:	return 0xff;	// Undefined.
+
+		case 0x20:	return 0x00;	// Data register.
+
+		case 0x40:
+		case 0x60:
+		return (mode_&0x1f);		// Status register.
+
+		case 0x80:
+		case 0xa0:
+		return 0x80;				// Handshake register.
+	}
+}
+
+void IWM::write(int address, uint8_t input) {
+	access(address);
+
+	switch(q_switches_) {
+		default:
+		break;
+
+		case 0xc0:	// Write mode register.
+			mode_ = input;
+		break;
+
+		case 0xd0:	// Write data register.
+		break;
+
+	}
+}
+
+void IWM::access(int address) {
+	switch(address & 0xf) {
+		default:
+		break;
+
+		case 0x8:	q_switches_ &= ~0x20;			break;
+		case 0x9:	q_switches_ |= 0x20;			break;
+		case 0xc:	q_switches_ &= ~0x40;			break;
+		case 0xd:	q_switches_ |= 0x40;			break;
+		case 0xe:	q_switches_ &= ~0x80;			break;
+		case 0xf:	q_switches_ |= 0x80;			break;
+	}
+}
+
+void IWM::run_for(const Cycles cycles) {
+}