src/main/java/com/loomcom/symon/devices/Acia.java

/*
 * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

package com.loomcom.symon.devices;

import com.loomcom.symon.exceptions.MemoryRangeException;

/**
 * Abstract base class for ACIAS such as the 6551 and 6580
 */

public abstract class Acia extends Device {

	/**
	 * Register addresses
	 */
	boolean receiveIrqEnabled = false;
	boolean transmitIrqEnabled = false;
	boolean overrun = false;

	long lastTxWrite = 0;
	long lastRxRead = 0;
	int baudRate = 0;
	long baudRateDelay = 0;

	/**
	 * Read/Write buffers
	 */
	int rxChar = 0;
	int txChar = 0;

	boolean rxFull = false;
	boolean txEmpty = true;

	public Acia(int address, int size, String name) throws MemoryRangeException {
		super(address, size, name);
	}

	/*
	 * Calculate the delay in nanoseconds between successive read/write operations, based on the
	 * configured baud rate.
	 */
	private long calculateBaudRateDelay() {
		if (baudRate > 0) {
			// TODO: This is a pretty rough approximation based on 8 bits per character,
			// and 1/baudRate per bit. It could certainly be improved
			return (long) ((1.0 / baudRate) * 1000000000 * 8);
		} else {
			return 0;
		}
	}

	/**
	 * @return The simulated baud rate in bps.
	 */
	public int getBaudRate() {
		return baudRate;
	}

	/**
	 * Set the baud rate of the simulated ACIA.
	 *
	 * @param rate The baud rate in bps. 0 means no simulated baud rate delay.
	 */
	public void setBaudRate(int rate) {
		this.baudRate = rate;
		this.baudRateDelay = calculateBaudRateDelay();
	}

	/**
	 * @return The contents of the status register.
	 */
	public abstract int statusReg();

	public synchronized int rxRead() {
		lastRxRead = System.nanoTime();
		overrun = false;
		rxFull = false;
		return rxChar;
	}

	public synchronized void rxWrite(int data) {
		if (rxFull) {
			overrun = true;
		}

		rxFull = true;

		if (receiveIrqEnabled) {
			getBus().assertIrq();
		}

		rxChar = data;
	}

	public synchronized int txRead() {
		txEmpty = true;

		if (transmitIrqEnabled) {
			getBus().assertIrq();
		}

		return txChar;
	}

	public synchronized void txWrite(int data) {
		lastTxWrite = System.nanoTime();
		txChar = data;
		txEmpty = false;
	}

	/**
	 * @return true if there is character data in the TX register.
	 */
	public boolean hasTxChar() {
		return !txEmpty;
	}

	/**
	 * @return true if there is character data in the RX register.
	 */
	public boolean hasRxChar() {
		return rxFull;
	}

}