Below is table that indicates which control lines are set for each type of instr

Question

Below is table that indicates which control lines are set for each type of instruction for the single- cycle implementation shown in Figure 4.24 of your textbook, which is also shown on the following page. Indi- cate the setting for each control line to support the addiu instruction, which should not require any modi- fications to the datapath. Use an X if the value for the control line does not matter. (30 points) ALU ALU RegALUMemto Reg MemMem DstSrc Instruction BranchJump Reg Write Read Write R-format SW beq addiu Modify the datapath and control for the single-cycle implementation shown on the following page to add the instruction jr (jump register). You should also indicate each of the appropriate settings for the control lines to support the jr instruction in the table above. You can assume that the opcode field uniquely identi- fies the jr instruction. (40 points)

Explanation / Answer

Alternatively the other solution (LUI ALT)

would not require any changes to the data path

and would feed the zero extended (Extend=0) of

Instruction[15-0] to the

second input of the ALU

(ALUSrc=1), set the ALUOp bits=11 for a logical 16-bit left shift operation at the ALU specified by

the ALU control, then set MemtoReg=0, set RegWri

te=1 and set RegDst=0 to write the ALU result

to Reg Rt.

The concept of the “critical pa

th” , the longest possible path

in the machine, was introduced in 5.4 on

page 315. Based on your understanding of

the single-cycle impl

ementation, show which units can

tolerate more delays (i.e. a

re not on the critical path), and w

hich units can benefit from hardware

optimization. Quantify your answe

rs taking the same numbers pr

esented on page 315.

Longest path is load instructi

on (instruction memory, register

file, ALU, data memory, register file). It

can benefit by optimizing the hardware

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