/// <summary>
/// Resets the CPU, then starts the execution process
/// </summary>
public void Reset(BreakpointMgr bpm)
{
// This will cause a hard reset
// to run programme at $fffc/$fffd
PC = 0xFFFC;
// Reset stack
SP = 0xFF;
// Force 6502 to use 0x4C as first opcode on swith on. This is a
// JMP $FFFC - a direct JMP.
Opcode = 0x4C;
PC--;
debugHeader = 0;
// Loop provided memory not toally shafted. In real life this doesn't happen,
// the CPU blindly reads the byte and hopes it can do something with it.
while (Opcode != 0)
{
Cycle c = new Cycle(PC);
// Print the header, allows us to see the opcode and PC
// when things go very wrong.
DebugHeader(Opcode);
// In reality, we could strip out the C below as that is used just for
// visual purposes....
ExecuteInstruction(c, Opcode);
// Output all registers and flags
DebugTail(c, bpm);
Opcode = RAM.GetByte(c, PC);
}
}
/// <summary>
/// Output various information to the console. Visual only.
/// </summary>
/// <param name="c"></param>
private void DebugTail(Cycle c, BreakpointMgr bpm)
{
Console.ForegroundColor = ConsoleColor.Green;
Console.Write(c.DebugRow().PadRight(30));
Console.ForegroundColor = ConsoleColor.Yellow;
Console.Write(String.Format(" {0:x2} {1:x2} {2:x2} {3:x2} ", A, X, Y, SP));
Console.ForegroundColor = ConsoleColor.DarkCyan;
Console.Write(ToBinary(Flags));
Console.ForegroundColor = ConsoleColor.Blue;
Console.Write(" " + c.Operand.Cycles + "+" + c.Operand.ExtraCycles + ":");
if (c.ActualCycles < c.Operand.Cycles || c.ActualCycles > c.Operand.Cycles + c.Operand.ExtraCycles)
{
Console.ForegroundColor = ConsoleColor.Yellow;
}
Console.WriteLine(c.ActualCycles);
BreakPointSet bps = bpm.ShallIBreak(this, c);
if (bps != null || bpm.StepMode)
{
if (bps != null)
{
Console.ForegroundColor = ConsoleColor.Yellow;
Console.WriteLine(bps);
}
var key = Console.ReadKey();
if (key.Key == ConsoleKey.Enter)
{
bpm.StepMode = false;
}
else
{
bpm.StepMode = true;
}
}
}
static void Main(string[] args)
{
Console.WriteLine("6502 Emulator\n");
CPU cpu = new CPU();
// Emulate the 6502 start up, which looks for a vector at $FFFC/$FFFD
// and starts execution from there. Need to start one code before as
// we musn't have zero at the load point - any value other than 0 good.
// This is not required if we don't mind blue screen of death situations
cpu.RAM.LoadMemnory(0xFFFB, new byte[] { 0xff, 0x00, 0x50 });
// Variables for testing - including JMP($) for subroutine
cpu.RAM.LoadMemnory(0x0302, new byte[] { 0xaa, 0xbb, 23, 0x50 });
// JSR and RET Subroutine Test
cpu.RAM.LoadMemnory(0x6040, new byte[] { 0xa2, 0x05, 0x8a, 0xaa, 0xc8, 0x98, 0xc8, 0xa8, 0x88, 0xe8, 0xca, 0x60 });
// Main code. Tests nearly all functions, then finally JMPs to Fibonacci code
cpu.RAM.LoadMemnory(0x5000, new byte[] { 0x6c, 0x04, 0x03, 0xa1, 0xed, 0xa1, 0x00, 0xa1, 0xed, 0xa9, 0x01, 0xbd, 0x02, 0x01, 0xb1, 0xff, 0xa2, 127,
0xe8, 0xa2, 0xff, 0xe8, 0xca, 0xd0, 0x01, 0xea, 0xa2, 0x04, 0xca, 0xd0, 0xfd, 0xca, 0x20, 0x40, 0x60, 0xEA, 0x38, 0x18,
0xf8, 0xd8, 0x78, 0x58, 0x8d, 0x00, 0x40, 0xa9, 0x0, 0xad, 0x00, 0x40, 0x8e, 0x00, 0x40, 0xad, 0x00, 0x40,
0x4c, 0x00, 0x70 });
// Fibonacci Sequence
cpu.RAM.LoadMemnory(0x7000, new byte[] { 0xa0, 0x07, 0xa9, 0x00, 0x8d, 0x00, 0x40, 0xa9, 0x01,
0xaa, 0x18, 0x6d, 0x00, 0x40, 0x8e, 0x00, 0x40, 0x88, 0xd0, 0xf5, 0xea });
// Add some breakpoints for fun.
BreakpointMgr mgr = new BreakpointMgr();
BreakPointSet bps = new BreakPointSet(5, "5th time at 0x700e");
mgr.AddBreakPointSet(bps);
bps.AddBreakPoint("PC", 0x700e);
BreakPointSet bps2 = new BreakPointSet(1, "A = 8 and Y=2 for the first time");
mgr.AddBreakPointSet(bps2);
bps2.AddBreakPoint("A", 0x08);
bps2.AddBreakPoint("Y", 0x02);
// You dont need to name the break point, and if you dont provide a count
// it will assume the first time the breakpoint is hit.
BreakPointSet bps3 = new BreakPointSet();
mgr.AddBreakPointSet(bps3);
bps3.AddBreakPoint("Opcode", 0x18);
BreakPointSet bps4 = new BreakPointSet(1, "Stack has exactly one entry on");
mgr.AddBreakPointSet(bps4);
bps4.AddBreakPoint("SP", 0xfd);
BreakPointSet bps5 = new BreakPointSet(1, "Carry flag set");
mgr.AddBreakPointSet(bps5);
bps5.AddBreakPoint("C", 0x1);
// Simulate a reset and start the execution
cpu.Reset(mgr);
}