CPU Design

CS252/Culler Lec 1.2 1/22/02 Levels of Representation (61C Review) High Level Language Program Assembly Language Program Machine Language Program Control Signal Specification Compiler Assembler Machine Interpretation temp = v[k]; v[k] = v[k+1]; v[k+1] = temp; lw$15,0($2) lw$16,4($2) sw$16,0($2) sw$15,4($2) °°°° ALUOP[0:3] <= InstReg[9:11] & MASK

CS252/Culler Lec 1.3 1/22/02 Execution Cycle Instruction Fetch Instruction Decode Operand Fetch Execute Result Store Next Instruction Obtain instruction from program storage Determine required actions and instruction size Locate and obtain operand data Compute result value or status Deposit results in storage for later use Determine successor instruction

4 Edge triggered D Flip-Flop Clk D Q Output changes only on the rising edge of the clock

CS252/Culler Lec 1.5 1/22/02 What’s a Clock Cycle? Old days: 10 levels of gates Today: determined by numerous time-of- flight issues + gate delays –clock propagation, wire lengths, drivers Latch or register combinational logic

In-Out control

Instruction 00

? ??? 00 IR ??? ALU Ctrl +1 PC Out In Beginning, Program & Data in Memory Reset counter, the Machine in a random state …. MAR MDR

??? ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

??? ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute... In  Accu IR AB 102

12 JNext instruction: 01

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute... IR[adr]  MAR, Accu  MDR,Write IR AB ACCU

16 JNext instruction: 02

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute... In  Accu IR AB 304

20 JNext instruction: 03

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR IR AB ACCU Instruction Execute... IR[adr]  MAR, Accu  MDR,Write

24 JNext instruction: 04

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute (1)... IR[adress]  MAR, Read IR AB ACCU

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute (2)... ACCU - MDR  ACCU IR AB ACCU 304

29 JNext instruction: 05

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute... (acc ≥ 0  IR[adress]  PC) IR AB ACCU

33 JNext instruction: 08

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute... ACCU  OUT IR AB ACCU 202

37 JNext instruction: 09

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (1)... PC  MAR, Read IR

ALU Ctrl +1 PC Out In MAR MDR Instruction Fetch (2)... MDR  IR, PC  1 IR AB

ALU Ctrl +1 PC Out In MAR MDR Instruction Execute... HLT IR AB ACCU