private void Decode()
{
int maxDecode = 0;
while (!DE_RN.Stalled && FE_DE.Instructions.Count > 0 && maxDecode < 4)
{
IData d = FE_DE.Instructions.Dequeue();
UInt32 i = d.Data;
DecodedOp op;
op.PC = d.PC;
op.Op = (byte)(i >> 25);
op.Const = (UInt32)(i >> 4) & 0x1FFFFFU;
op.Var = (UInt32)(i >> 8) & 0x1FFFF;
op.Dst = (byte)((i >> 8) & 0xf);
op.Src1 = (byte)((i >> 4) & 0xf);
op.Src2 = (byte)((i >> 0) & 0xf);
OpCodes.OpInfo opd = OpCodes.GetInfo((OpCodes.Op)op.Op);
op.Meta = opd;
DE_RN.Ops.Enqueue(op);
// Optimization: Check op is a branch and if it is use branch prediction
// to load in new instructions and do a partial pipeline flush.
maxDecode++;
}
// Renamer is stalled for some reason, we will have to stall and propogate stall to fetch stage.
FE_DE.Stalled = DE_RN.Stalled && FE_DE.Instructions.Count >= 4;
this.StalledDecodeCycles += (4 - maxDecode);
}
private void Rename()
{
int maxRename = 0;
while (PhysFreeList.PhysicalRegisterAvailable() && !this.IQueue.IsFull() && !ROB.Full() && DE_RN.Ops.Count > 0 && maxRename < 4)
{
DecodedOp o = DE_RN.Ops.Dequeue();
byte op = o.Op;
OpCodes.OpInfo opi = o.Meta;
byte dst = 0;
if (opi.HasOutput)
{
// TODO: Don't cast this. Do it properly.
dst = (byte)PhysFreeList.GetUnusedRegister();
PhysRegisters.SetReady(dst, false);
}
byte src1 = (byte)ArchToPhysTable.GetPhysicalRegisterId(opi.Src1Dep ? o.Src1 : 0);
byte src2 = (byte)ArchToPhysTable.GetPhysicalRegisterId(opi.Src2Dep ? o.Src2 : 0);
bool rd1 = opi.Src1Dep ? PhysRegisters.IsReady(src1) : true;
bool rd2 = opi.Src2Dep ? PhysRegisters.IsReady(src2) : true;
if (opi.HasOutput)
{
byte archReg = 0;
switch (opi.OutputSource)
{
case OpCodes.DstSource.Dst:
archReg = o.Dst;
break;
case OpCodes.DstSource.Src1:
archReg = o.Src1;
break;
case OpCodes.DstSource.Src2:
archReg = o.Src2;
break;
}
ArchToPhysTable.MapArchToPhys(archReg, dst);
// Redirect dst register to the correct destination.
o.Dst = archReg;
}
// Resulting register of this operation should be declared not ready until it has executed.
Console.WriteLine("Rename: rd1={0}, rd2={1}, src1={2}, src2={3}, dst={4}", rd1, rd2, (int)src1, (int)src2, (int)dst);
// Add entry to issue queue and re-order buffer
this.IQueue.AddToQueue(o.PC, op, src1, src2, dst, rd1, rd2, o.Const, o.Meta);
this.ROB.AddToQueue(o.PC, o.Dst, dst, o.Meta.HasOutput);
maxRename++;
}
// Stallable by multiple resource hazards: re-order buffer full, issue queue full or lack of physical registers.
// Therefore a stall may occur, resulting in wasted cycles.
this.DE_RN.Stalled = !PhysFreeList.PhysicalRegisterAvailable() || this.IQueue.IsFull() || ROB.Full() || DE_RN.Ops.Count >= 4;
this.StalledRenameCycles += (4 - maxRename);
}
public void AddToQueue(UInt32 pc, byte op, byte src1, byte src2, byte dst, bool rd1, bool rd2, UInt32 constant, OpCodes.OpInfo info)
{
Debug.Assert(!IsFull());
IQueue.Add(new Entry()
{
PC = pc, Op = op, Src1 = src1, Src2 = src2, Rd1 = rd1, Rd2 = rd2, Dst = dst, Const = constant, Meta = info
});
}