CS104 Computer Organization and Design

CS104 Computer Organization and Design Datapaths

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Admin •  Homework •  Homework 4 out tonight •  Due Monday March 26th •  Download/check your submissions

•  Reading: •  Chapter 4 •  (Maybe review 1.4)

•  Midterm 2 •  March 28

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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What did we do last week? •  Who can remind us what we did last week?

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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What did we do last week? •  Who can remind us what we did last week? •  •  •  •  • 

Ski Go to the beach Sleep in Read a book …

•  Ok, but seriously?

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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When last I saw you all.. •  Last time I was here (Feb 27/29) •  Learned basics of logic design •  Gates (And, Or, Nor, …) •  Put gates together to make •  Muxes •  Adders •  Latches •  Flip-flops •  …

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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While I was at HPCA.. •  Prof. Lebeck started teaching you all about datapaths •  Putting logic together to execute instructions •  Started on single-cycle datapath

•  We’ll review/continue with single cycle •  Then jump into more things!

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Datapath for MIPS ISA •  Consider only the following instructions add $1,$2,$3 addi $1,2,$3 lw $1,4($3) sw $1,4($3) beq $1,$2,PC_relative_target j absolute_target

•  Why only these? •  Most other instructions are the same from datapath viewpoint •  The one’s that aren’t are left for you to figure out

CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Start With Fetch

+ 4

P C

Insn Mem

•  PC and instruction memory •  A +4 incrementer computes default next instruction PC CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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First Instruction: add

+ 4

P C

Insn Mem

Register File s1 s2 d

•  Add register file and ALU CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Second Instruction: addi

+ 4

P C

Insn Mem

Register File s1 s2 d S X

•  Destination register can now be either Rd or Rt •  Add sign extension unit and mux into second ALU input CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Third Instruction: lw

+ 4

P C

Insn Mem

a

Register File

Data d Mem

s1 s2 d S X

•  Add data memory, address is ALU output •  Add register write data mux to select memory output or ALU output CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Fourth Instruction: sw

+ 4

P C

Insn Mem

a

Register File

Data d Mem

s1 s2 d S X

•  Add path from second input register to data memory data input CS104 (Hilton): Datapaths [Slides adapted from A. Roth’s]

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Fifth Instruction: beq