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replace busy waiting to emulate "proper" CPU speed with some time book keeping and thread sleeping

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This commit is contained in:
Maik Merten 2014-07-19 20:19:26 +02:00
parent b266a02372
commit 44bfbc17ab
1 changed files with 21 additions and 5 deletions
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26
src/main/java/com/loomcom/symon/Cpu.java
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@ -25,6 +25,8 @@ package com.loomcom.symon;
import com.loomcom.symon.exceptions.MemoryAccessException;
import com.loomcom.symon.util.HexUtil;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* This class provides a simulation of the MOS 6502 CPU's state machine.
@ -75,6 +77,10 @@ public class Cpu implements InstructionTable {
/* Internal scratch space */
private int lo = 0, hi = 0; // Used in address calculation
private int tmp; // Temporary storage
/* Accounting for non-busy CPU waiting */
private long opBeginTime;
private long surplusTime;
/**
* Construct a new CPU.
@ -157,6 +163,7 @@ public class Cpu implements InstructionTable {
* Performs an individual instruction cycle.
*/
public void step() throws MemoryAccessException {
opBeginTime = System.nanoTime();
// Store the address from which the IR was read, for debugging
state.lastPc = state.pc;
@ -1324,11 +1331,20 @@ public class Cpu implements InstructionTable {
if (clockSteps == 0) {
clockSteps = 1;
}
long startTime = System.nanoTime();
long stopTime = startTime + (CLOCK_IN_NS * clockSteps);
// Busy loop
while (System.nanoTime() < stopTime) {
;
long opFinishTime = System.nanoTime();
long timeSpent = opFinishTime - opBeginTime;
if(timeSpent < clockSteps) {
surplusTime += clockSteps - timeSpent;
// look if a reasonable amount of time has accumulated
if(surplusTime > 1000 * 1000 * 10) {
try {
// sleep away the surplus time
Thread.sleep(surplusTime / (1000 * 1000));
} catch (InterruptedException ex) {
Logger.getLogger(Cpu.class.getName()).log(Level.SEVERE, "Trouble putting the CPU to sleep", ex);
}
surplusTime = 0;
}
}
}