designKilla: The 32-bit pipelined processor

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designKillaThe 32-bit pipelined processor

• Brought to you by
• Victoria Farthing
• Dat Huynh
• Jerry Felker
• Tony Chen
• Supervisor Young Cho

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32-Bit RISC Pipelined Processor

• Reduced Instruction Set allows for faster
  execution of simple, frequently used instructions
  which can be combined to achieve the same result
  as a single, slower CISC instruction
• Pipelining allows a faster clock cycle and less
  wasted resources

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Datapath Pipeline Stages

• 5 Stages
• Instruction Fetch
• Instruction Decode
• Execution
• Memory Write
• Write Back

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Unique Data Path Features

• Next instruction address calculation
• For basic incrementation, the address is
  calculated by a counter

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Address Jump Calculations

• For address jumps, there is a 19-bit load port on
  the counter
• The loaded address comes from an adder with
  multiplexed inputs
• Load bit is controlled by a comparator (beq)
  or-ed with the absolute jump control bit

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Double Clocked Memory Interface

• Problem One Memory for both Instruction and
  Data
• Solution Double Clock!
• Access the memory twice during one clock cycle

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Double Clocked Memory Interface
Write Enable
Fast Clock
Clock
Fetch Instruction
Fetch Data
Fetch Instruction
Write Data

• Fetches Instruction in First Cycle
• Fetches or Writes Data In Second Cycle
• Data is output by end of Clock Cycle

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Unique Data Path Features

• Structural Multiplier
• 16 X 16 bit
• Multi-level creation
• Four 8 X 8 bit multipliers
• Each containing four 4 X 4 bit multipliers
• Each comprised of a cascaded network of full and
  half adders, built on logic gates

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16-Bit Multiplier Unit

• Based On Hand Multiplication
• Made Up of Networkof AND Gatesand Adders

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Why 32 ? 16 bit?

• 32bit x 32bit 64 bits!
• Multiple complex changes to existing architecture
  would be required
• Only one register can be written per clock cycle
• Could hold value for next cycle or stall the
  pipeline
• Would require pseudoinstruction as well as new
  hardware and multiple control signals

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Use pseudo-code instruction mult32
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Improve the Multiplier

• Can decrease the latency of a combinational
  multiplier with carry-look ahead adding methods.
• Small amount of extra hardware needed, worth it
  if multiplier has largest latency.

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Other Multiplier Topologies

• Shifting multiplication
• Shift multiplicand several times based on
  multiplier bits
• Add intermediate shifted values

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Other Multiplier Topologies

• Pipelined multiplication
• Store intermediate sums
• Allows for faster clock cycle if traditional
  combinational multiplication presents the
  critical path

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Other Multiplier Topologies

• Pipelined multiplication
• Sequential multiplication
• Useful to minimize hardware waste if
  multiplication is an infrequent operation
• Continues to allow for faster clock cycle if
  traditional combinational multiplication presents
  the critical path

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Instruction Set Architecture
R-Type
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I-Type
J-Type
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The Assembler

• Converts assembly code to binary representation

Add 3,1,2 gt 0000000001000100001100000000000
16-bit wide memory modules Split into high and
low bits for output
000000000100010 gt High 0001100000000000 gt Low
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Assembler Features

• Allows for labels to be used in loops
• Automatically calculates offsets based on label
  position
• LABEL add 1,2,3
• jmp LABEL
• Resolves hazards created by pipelining
• Automatically determines the appropriate number
  of NO-OPS to insert based on relative position of
  consecutive instructions

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Design allows for pseudo-instructions to be
used Pseudo Instruction HLT Actual
Instructions H1 JMP H1 NOP NOP
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Topic 2 Design Compiler

• Bison - Parser
• A compiler compiler
• A grammar generator
• -------------------------
• Flex Lexer
• A Fast lexical analyzer
• Tool used in pattern matching on text

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Compiling The C Language

• Interface Lexer and Parser
• Lex will feed tokens to Bison (YACC)
• A grammar tree is generated

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Source code to run-time
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A simple program

• A simple C program
• void main ( void )
• int b
• int d
• int x
• int y 3
• int g
• x b d
• g y x

• Assembly Code Equivalent
• lwi 4, 0, 3
• add 6, 1, 2
• sw 3, 6, 0
• add 6, 4, 3
• sw 5, 6, 0

• Machine Code Instructions

• Memory High
• 0 0000110000000100
• 1 0000000000100010
• 2 0000000000000000
• 3 0000000000000000
• 4 0000000000000000
• 5 0000000000000000
• 6 0000000000000000
• 7 0000100011000011
• 8 0000000000000000
• 9 0000000000000000
• 10 0000000000000000
• 11 0000000010000011
• 12 0000000000000000
• 13 0000000000000000
• 14 0000000000000000
• 15 0000000000000000
• 16 0000000000000000
• 17 0000100011000101

• Memory Low
• 0 0000000000000011
• 1 0011000000000000
• 2 0000000000000000
• 3 0000000000000000
• 4 0000000000000000
• 5 0000000000000000
• 6 0000000000000000
• 7 0000000000000000
• 8 0000000000000000
• 9 0000000000000000
• 10 0000000000000000
• 11 0011000000000000
• 12 0000000000000000
• 13 0000000000000000
• 14 0000000000000000
• 15 0000000000000000
• 16 0000000000000000
• 17 0000000000000000

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Could Use a Little Work

• Currently the Processor could use a little work
  to improve performance.
• Decreased memory latency would be largest and
  most direct improvement to processor.
• Must optimize ALU as well as multiplier unit.
• All in all, will work but not ready for
  commercial usage.

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References
Computer Organization and Design The Hardware
Software Interface (2nd Ed) Patterson, David A.
and Hennessy, John L. Morgan Kaufman
Publishers, 1997 Introduction to
Compilers http//cs.wwc.edu/aabyan/221_2/PLBOOK/
Translation.html Aaby, Anthony A., 1998 The
Compiler Design Handbook Srikant, Y. N. and
Shankar, Priti CRC Press, 2002
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THE END

• Questions?