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Timing and UI enhancements.

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This change introduces simulated baud rates in the ACIA. Baud rate is controlled just as in the real 6551, by writing to the ACIA's control register. Baud rates between 50 and 19,200 baud are selectable. A baud rate of 0 has special meaning, and turns off all simulated baud rate delays (on a real 6551, this means to use an external clock instead of the internal baud rate generator)

A busy-wait loop between steps in the simulator control program has also been added. This uses the high-resolution 'System.nanoTime()' call to wait a specific number of nanoseconds before continuing. Symon now waits at least 1uS between clock cycles, trying to approach a real 1MHz 6502 in performance. It is far from perfect, but it's better than it was.

 Also refactored the status panel to use a BoxLayout, and DRY-up some of the code.
This commit is contained in:
Seth Morabito committed 2012-10-14 17:56:19 -07:00
1 parent 6c0ff5a5b2
commit c1caf8c6b4
9 files changed
+272 -128
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src/main/java/com/loomcom/symon/devices/Acia.java
+135 -11
View File
@@ -2,6 +2,9 @@ package com.loomcom.symon.devices;
import com.loomcom.symon.exceptions.*;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* This is a simulation of the MOS 6551 ACIA, with limited
@@ -34,14 +37,19 @@ public class Acia extends Device {
private boolean overrun = false;
private long lastTxWrite = 0;
private long lastRxRead = 0;
private int baudRate = 0;
private long baudRateDelay = 0;
/**
* Read/Write buffers
*/
private int rxChar = 0;
private int txChar = 0;
private boolean rxFull = false;
private boolean txFull = false;
private boolean rxFull = false;
private boolean txEmpty = true;
public Acia(int address) throws MemoryRangeException {
super(address, ACIA_SIZE, "ACIA");
@@ -54,10 +62,7 @@ public class Acia extends Device {
case DATA_REG:
return rxRead();
case STAT_REG:
// TODO: Overrun, Parity Error, Framing Error,
// DTR, DSR, and Interrupt flags.
return ((rxFull ? 0x08 : 0x00) |
(txFull ? 0x00 : 0x10));
return statusReg();
case CMND_REG:
return commandRegister;
case CTRL_REG:
@@ -80,19 +85,137 @@ public class Acia extends Device {
commandRegister = data;
break;
case 3:
controlRegister = data;
setControlRegister(data);
break;
default:
throw new MemoryAccessException("No register.");
}
}
/**
* Set the control register and associated state.
*
* @param data
*/
public void setControlRegister(int data) {
this.controlRegister = data;
// If the value of the data is 0, this is a request to reset,
// otherwise it's a control update.
if (data == 0) {
reset();
} else {
// Mask the lower three bits to get the baud rate.
int baudSelector = data & 0x0f;
switch (baudSelector) {
case 0:
baudRate = 0;
break;
case 1:
baudRate = 50;
break;
case 2:
baudRate = 75;
break;
case 3:
baudRate = 110; // Real rate is actually 109.92
break;
case 4:
baudRate = 135; // Real rate is actually 134.58
break;
case 5:
baudRate = 150;
break;
case 6:
baudRate = 300;
break;
case 7:
baudRate = 600;
break;
case 8:
baudRate = 1200;
break;
case 9:
baudRate = 1800;
break;
case 10:
baudRate = 2400;
break;
case 11:
baudRate = 3600;
break;
case 12:
baudRate = 4800;
break;
case 13:
baudRate = 7200;
break;
case 14:
baudRate = 9600;
break;
case 15:
baudRate = 19200;
break;
}
// Recalculate the baud rate delay.
baudRateDelay = calculateBaudRateDelay();
}
}
/*
* Calculate the delay in nanoseconds between successive read/write operations, based on the
* configured baud rate.
*/
private long calculateBaudRateDelay() {
if (baudRate > 0) {
// This is a pretty rough approximation based on 8 bits per character,
// and 1/baudRate per bit.
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;
}
/**
* @return The contents of the status register.
*/
public int statusReg() {
// TODO: Overrun, Parity Error, Framing Error, DTR, DSR, and Interrupt flags.
int stat = 0;
if (rxFull && System.nanoTime() >= (lastRxRead + baudRateDelay)) {
stat |= 0x08;
}
if (txEmpty && System.nanoTime() >= (lastTxWrite + baudRateDelay)) {
stat |= 0x10;
}
return stat;
}
@Override
public String toString() {
return "ACIA@" + String.format("%04X", baseAddress);
}
public synchronized int rxRead() {
lastRxRead = System.nanoTime();
rxFull = false;
return rxChar;
}
@@ -103,12 +226,13 @@ public class Acia extends Device {
}
public synchronized int txRead() {
txFull = false;
txEmpty = true;
return txChar;
}
public synchronized void txWrite(int data) {
txFull = true;
lastTxWrite = System.nanoTime();
txEmpty = false;
txChar = data;
}
@@ -116,7 +240,7 @@ public class Acia extends Device {
* @return true if there is character data in the TX register.
*/
public boolean hasTxChar() {
return txFull;
return !txEmpty;
}
/**
@@ -128,7 +252,7 @@ public class Acia extends Device {
private synchronized void reset() {
txChar = 0;
txFull = false;
txEmpty = true;
rxChar = 0;
rxFull = false;
}