/// <summary>
/// FUNCTION:
/// -Using instruction field update fields: instructionString, opcode, Rn, Rd, operand2.
/// </summary>
public void decodeDP()
{
// update field: instructionString, opcode
opcode = (instruction >> 21) & 0xf;
updateInstructionName();
// update field Rn
Rn = (instruction >> 16) & 0xf;
// update field RnRegVal
// if Rn is PC, then RnRegVal should be currentAddress + 8 bytes. else it it's the content of register Rn
if (Rn == 15)
{
RnRegVal = instructAddress + 8;
}
else
{
RnRegVal = registers.getRegNValue(Rn);
}
// update field Rd
Rd = (instruction >> 12) & 0xf;
/* Decode the operand2 of the intruction and update field operand2
* Steps to do this:
* 1. check bits 25 & 4 for operand 2 types
* 2. if 8 bit immediate
* initialize _8BitImmediate object and decode_Imm
* if register or immediate shifted register
* initialize RegAndImmShReg object and decode_Imm
* if register shifted register
* initialize RegShReg object and decode_Imm
*/
if (bit25 == true) // Immediate
{
immediate = new Immediate(memory, registers, instruction, instructAddress);
immediate.decode_Imm();
}
if (bit25 == false && bit4 == false) // Register and Immediate Shifted Register
{
reg_and_imm_sh_reg = new RegAndImmShReg(memory, registers, instruction, instructAddress);
reg_and_imm_sh_reg.decode_RegAndImmShReg();
}
// TODO: not implemented in sim I
if (this.bit25 == false && this.bit4 == true) // Register Shifted Register
{
this.reg_sh_reg = new RegShReg(this.memory, this.registers, this.instruction, this.instructAddress);
this.reg_sh_reg.decode_RegShReg();
}
}
private bool bit4; //data processing addressing mode flag
public DataProcessing(Memory _memory, Registers _registers, uint _currentInstruction, uint _currentInstAddress)
{
this.instructionString = "Not Found Yet";
this.instruction = _currentInstruction;
this.instructAddress = _currentInstAddress;
// initialize operand2 types to null
this.immediate = null;
this.reg_and_imm_sh_reg = null;
this.reg_sh_reg = null;
// hook up registers and mememory object references
this.registers = _registers;
this.memory = _memory;
// setting up data processing addressing mode flags // -4 because pc gor incremented by 4 bytes when the instruction was fetched
this.bit25 = memory.TestFlag(registers.getProgramCounter() - 4, 25); //data processing addressing mode flag
this.bit4 = memory.TestFlag(registers.getProgramCounter() - 4, 4); //data processing addressing mode flag
}