Question

Consider the following assembly language code:

I0: add $R4,$R1,$R0                             //ADD R4 = R1 + R0;

I1: lw $R1,100($R3)                             //LDW R1 = MEM[R3 + 100];

I2: lw $R9,4,($R1)                                // LDW R9 = MEM[R1 + 4];

I3: add $R3,$R4,$R9                             //ADD R3 = R4 + R9;

I4: lw $R1,0($R3)                                 //LDW R1 = MEM[R3 + 0];

I5: sub $R3,$R1,$R4                             //SUB R3 = R1 - R4;

I6: and $R9,$R9,$R7                             //AND R9 = R9 & R7;

I7: sw $R2,100($R4)                             //STW MEM[R4 + 100] = R2;

I8: and $R4,$R2,$R1                             //AND R4 = R2 & R1;

I9: add $R1,$R5,$R4                             //ADD R1 = R5 + R4;

Consider a pipeline with forwarding, hazard detection, and 1 delay slot for branches. The pipeline is the typical 5-stage IF, ID, EX, MEM, WB MIPS design. For the above code, complete the pipeline diagram below (instructions on the left, cycles on top) for the code. Insert the characters IF, ID, EX, MEM, WB for each instruction in the boxes. Assume that there two levels of bypassing, that the second half of the decode stage performs a read of source registers, and that the first half of the write-back stage writes to the register file. Label all data stalls (Draw an X in the box). Label all data forwards that the forwarding unit detects (arrow between the stages handing off the data and the stages receiving the data).

Answer 1