The GPR Environment (Mueller & Paul)

1. The GPR Environment (Mueller & Paul) GPR_WE

2. The GPR Environment (Cont.) GPR_WE Drivers to enable the writing of a value to the bus.

3. The GPR Environment (Cont.) GPR_WE A1, A2 are the registers to be read from and A3 is the register to be written to. Their values are trivial-derived from the IR register.

4. The GPR Environment (Cont.) GPR_WE R0 always equals zero: Zero Testers check if A1 or A2 equal zero.If so, the A1Zero / A2Zero signals equal zero.

5. The GPR Environment (Cont.) GPR_WE a read from R0 results with a zero value written to the appropriate register (A or B).

6. The GPR Environment (Cont.) GPR_WE A3 can be either IR[15:11], IR[20:16] or 11111. Its value is according to the instruction’s type (I-Type or R-Type). The I-Type Control signal “decides” what type of instruction we deal with.

7. The GPR Environment (Cont.) GPR_WE When dealing with the jalr instruction, we have to write to R31 and at that case, the Jlink signal gets the value of 1.

8. The GPR Environment (Cont.) GPR_WE Remember: The GPR Env. is a dual-port RAM that supports either two Read operations or one write operation at a certain time.

9. The PC Environment The PC Env. is implemented as follows: This constant is used in the Decode stage when advancing the PC to be PC+1 When the computer is turned on, the PUP signal=1 , the MUX and the Control signal PCsce get a “1” value and as a result the PC is initialized to the address. The DINT bus feeds the new PC.

10. The ALU Environment ALU • The ALU supports: • 2’s complement integer addition operations • 2’s complement integer subtraction operations • Comparison operations • Bitwise logical operations • A comparison is implemented by subtraction and • examination of a sign-bit and a zero-tester