//Extract adress according to register offset specification
int DecodeRegisterOffset()
{
char Rm = (char)ExtractBits(code, 0, 3);
char Sh = (char)ExtractBits(code, 5, 6);
int shiftVal = ExtractBits(code, 7, 11);
shiftVal *= U ? 1 : -1;
stringValue = ", " + (shiftVal == 0 ? (U ? "" : "-") : "") + "r" + (int)Rm;
int regval = Regs.ReadWord(GetReg(Rm));
if (Rm == 15)
{
regval += 8;
}
if (shiftVal != 0)
{
stringValue += ", " + BarrelShifter.CodeToString(Sh) + " #" + shiftVal;
}
else if (!U)
{
regval *= -1;
}
return(BarrelShifter.ShiftByCode(regval, shiftVal, Sh));
}
//fire the interrupt
//Interrupts are special. They get special access to the inner guts of the program...
public override void Execute()
{
if (swiType == 0x11)
{
Flags[SysFlag.Running] = false;
Flags[SysFlag.Unsteppable] = true;
return;
}
Regs.WriteWord(Reg.LR_SVC, Regs.ReadWord(Reg.R15));
Regs.WriteWord(Reg.SPSR_SVC, Regs.ReadWord(Reg.CPSR));
int cpsr = Regs.ReadWord(Reg.CPSR) & 0b1111111111111111111111111100000;
Regs.WriteWord(Reg.CPSR, cpsr | Mode.Supervisor); //switch to superviser
if (swiType == 0x0)
{
SetCPSRFlag(7, true);
}
else
{
SetCPSRFlag(7, false);
}
Regs.WriteWord(Reg.R15, 0x8);
}
//decode instruction based on 'code' parent variable and returns populated version of itself
public override Instruction Decode()
{
IBit = TestFlag(code, 25);
P = TestFlag(code, 24);
U = TestFlag(code, 23);
S = TestFlag(code, 22);
W = TestFlag(code, 21);
L = TestFlag(code, 20);
Rn = (char)ExtractBits(code, 16, 19);
address = Regs.ReadWord(GetReg(Rn));
regstr = "";
bool first = true;
for (int i = 0; i < regList.Length; i++)
{
regList[i] = TestFlag(code, i);
if (regList[i])
{
if (!first)
{
regstr += ", ";
}
regstr += "r" + i;
first = false;
}
}
return(this);
}
//stores the values in the active registers in reglist[] into the address pinted to by Rn
//while decrementing the value Rn before the store process
void Store() //push
{
for (int i = regList.Length - 1; i >= 0; i--)
{
if (regList[i])
{
address -= 4;
RAM.WriteWord(address, Regs.ReadWord(GetReg(i)));
}
}
}
//Extract the operands op1, op2, op3 from the command
void CalculateOperands()
{
opn = Regs.ReadWord(GetReg(Rn)); //What is stored in Rn
if (Rn == 15)
{
opn += 8;
}
opd = Regs.ReadWord(GetReg(Rd)); //What is stored in Rd
op3 = IBit ? CalulateImmediateOperand3() : CalculateRegisterOperand3();
}
//Transfers value from CPSR or SPSR of the current mode into a general purpose register
public override void Execute()
{
int value = Regs.ReadWord(Reg.CPSR);
if (RBit)
{
char mode = CheckMode();
if (mode == 'V') //supervisor
value = Regs.ReadWord(Reg.LR_SVC);
else if (mode == 'R') //irq
value = Regs.ReadWord(Reg.LR_IRQ);
}
Regs.WriteWord(GetReg(Rd), value);
}
//caculated and returns the reister operand
int CalulateRegValue()
{
char Rm = (char)ExtractBits(code, 0, 3);
int val = Regs.ReadWord(GetReg(Rm));
if (Rm == 15)
{
val += 8;
}
strVal = "r" + (int)Rm;
return(val);
}
//Change the value of the program counter,
//if L is true, store previous PC value in R14
public override void Execute()
{
if (isRet)
{
ExecuteReturn();
return;
}
if (link)
{
Regs.WriteWord(GetReg(14), Regs.ReadWord(Reg.R15));
}
Regs.WriteWord(Reg.R15, address);
}
//Calculate the address to jump to relative to PC
void ProcessBranchAddress()
{
int pc = Regs.ReadWord(Reg.R15);
link = TestFlag(code, 24);
sign = TestFlag(code, 23);
offset = ExtractBits(code, 0, 22);
if (sign)
{
uint mask = 0xFFF00000;
offset |= (int)mask; //mask to convert to signed FF000000
}
offset <<= 2;
address = pc + 8 + offset;
}
//Stores value from register Rd in 'address'
void Store()
{
if (B)
{
int storeVal = Regs.ReadWord(GetReg(Rd));
if (Rd == 15)
{
storeVal += 8;
}
RAM.WriteByte(address, (byte)storeVal);
}
else
{
int storeVal = Regs.ReadWord(GetReg(Rd));
if (Rd == 15)
{
storeVal += 8;
}
RAM.WriteWord(address, storeVal);
}
}
//Calcultes and returns the register shift operand
int CalculateRegisterOperand3()
{
int shiftVal;
Rm = (char)ExtractBits(code, 0, 3);
char Sh = (char)ExtractBits(code, 5, 6);
bool bit4 = TestFlag(code, 4);
char Rs = '0';
strShift = "r" + (int)Rm;
if (!bit4)
{
shiftVal = ExtractBits(code, 7, 11);
}
else
{
Rs = (char)ExtractBits(code, 8, 11);
shiftVal = Regs.ReadWord(GetReg(Rs));
if (Rs == 15)
{
shiftVal += 8;
}
}
if (shiftVal != 0)
{
strShift += ", " + BarrelShifter.CodeToString(Sh) + (bit4 ? " r" + (int)Rs : " #" + shiftVal);
}
int val = Regs.ReadWord(GetReg(Rm));
if (Rm == 15)
{
val += 8;
}
return(BarrelShifter.ShiftByCode(val, shiftVal, Sh));
}
//Decodes loadstore instruction for 'code' parent variable and returns
//itself as a fully populated instruction ready for execution
public override Instruction Decode()
{
IBit = TestFlag(code, 25);
P = TestFlag(code, 24);
U = TestFlag(code, 23);
B = TestFlag(code, 22);
W = TestFlag(code, 21);
L = TestFlag(code, 20);
Rn = (char)ExtractBits(code, 16, 19);
Rd = (char)ExtractBits(code, 12, 15);
int regContent = Regs.ReadWord(GetReg(Rn));
if (Rn == 15)
{
regContent += 8;
}
offset = !IBit?DecodeImmediateOffset() : DecodeRegisterOffset();
address = P ? regContent + offset : regContent;
return(this);
}
//performs the special case for the multiplication instruction,
//multiplies the values in Rm and Rn and stores their results in Rd
void ExecMUL()
{
Regs.WriteWord(GetReg(Rd), (Regs.ReadWord(GetReg(Rn)) * Regs.ReadWord(GetReg(Rm))));
}
//Execute BX: jump to address stored in link register
void ExecuteReturn()
{
Regs.WriteWord(Reg.R15, Regs.ReadWord(GetReg(Rm)));
}