turn Acia into an abstract class so that the 6551 and 6850 ACIAs can reuse code and an unified interface.
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/*
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* Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package com.loomcom.symon.devices;
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import com.loomcom.symon.exceptions.MemoryAccessException;
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import com.loomcom.symon.exceptions.MemoryRangeException;
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/**
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* This is a simulation of the MOS 6551 ACIA, with limited
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* functionality. Interrupts are not supported.
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* <p/>
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* Unlike a 16550 UART, the 6551 ACIA has only one-byte transmit and
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* receive buffers. It is the programmer's responsibility to check the
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* status (full or empty) for transmit and receive buffers before
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* writing / reading.
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*/
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public class Acia6551 extends Acia {
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public static final int ACIA_SIZE = 4;
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static final int DATA_REG = 0;
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static final int STAT_REG = 1;
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static final int CMND_REG = 2;
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static final int CTRL_REG = 3;
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/**
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* Registers. These are ignored in the current implementation.
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*/
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private int commandRegister;
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private int controlRegister;
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public Acia6551(int address) throws MemoryRangeException {
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super(address, ACIA_SIZE, "ACIA");
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}
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@Override
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public int read(int address) throws MemoryAccessException {
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switch (address) {
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case DATA_REG:
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return rxRead();
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case STAT_REG:
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return statusReg();
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case CMND_REG:
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return commandRegister;
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case CTRL_REG:
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return controlRegister;
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default:
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throw new MemoryAccessException("No register.");
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}
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}
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@Override
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public void write(int address, int data) throws MemoryAccessException {
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switch (address) {
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case 0:
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txWrite(data);
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break;
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case 1:
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reset();
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break;
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case 2:
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setCommandRegister(data);
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break;
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case 3:
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setControlRegister(data);
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break;
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default:
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throw new MemoryAccessException("No register.");
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}
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}
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private void setCommandRegister(int data) {
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commandRegister = data;
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// Bit 1 controls receiver IRQ behavior
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receiveIrqEnabled = (commandRegister & 0x02) == 0;
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// Bits 2 & 3 controls transmit IRQ behavior
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transmitIrqEnabled = (commandRegister & 0x08) == 0 && (commandRegister & 0x04) != 0;
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}
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/**
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* Set the control register and associated state.
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*
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* @param data
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*/
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private void setControlRegister(int data) {
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controlRegister = data;
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int rate = 0;
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// If the value of the data is 0, this is a request to reset,
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// otherwise it's a control update.
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if (data == 0) {
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reset();
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} else {
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// Mask the lower three bits to get the baud rate.
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int baudSelector = data & 0x0f;
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switch (baudSelector) {
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case 0:
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rate = 0;
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break;
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case 1:
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rate = 50;
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break;
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case 2:
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rate = 75;
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break;
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case 3:
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rate = 110; // Real rate is actually 109.92
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break;
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case 4:
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rate = 135; // Real rate is actually 134.58
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break;
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case 5:
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rate = 150;
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break;
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case 6:
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rate = 300;
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break;
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case 7:
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rate = 600;
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break;
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case 8:
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rate = 1200;
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break;
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case 9:
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rate = 1800;
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break;
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case 10:
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rate = 2400;
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break;
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case 11:
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rate = 3600;
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break;
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case 12:
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rate = 4800;
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break;
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case 13:
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rate = 7200;
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break;
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case 14:
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rate = 9600;
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break;
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case 15:
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rate = 19200;
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break;
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}
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setBaudRate(rate);
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}
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}
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/**
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* @return The contents of the status register.
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*/
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@Override
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public int statusReg() {
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// TODO: Overrun, Parity Error, Framing Error, DTR, DSR, and Interrupt flags.
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int stat = 0;
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if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
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stat |= 0x08;
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}
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if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
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stat |= 0x10;
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}
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return stat;
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}
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private synchronized void reset() {
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txChar = 0;
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txEmpty = true;
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rxChar = 0;
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rxFull = false;
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receiveIrqEnabled = false;
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transmitIrqEnabled = false;
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}
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}
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