Chapter 4.1 From Code To Hardware

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Clark UniversityComputer Science DepartmentCSCI
140 Computer OrganizationFrom Code To Hardware
Professor Jerry Breecher 2004
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The Plan

• We start with code.
• From that code we get a 32-bit equivalent binary
  representation.
• The binary maps what the hardware looks like.
• The hardware reads each of those fields.
• The hardware performs an operation.

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We Start With Code

• 
  
• This is code that mimics the following C
  program.
• main( )
• printf( "Hello World\n" )
• 
  
• .text
• .globl main
• main
• la a0, hello
• ori v0, 0, 4 li v0, 4
• add t0, t1, t2
• syscall
• jr ra
• .data
• hello

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From that code we get a 32-bit Equivalent Binary
Representation.

• 0x00400020 0x3c021001 lui 2, 4097 12
  la a0, hello
• 0x00400024 0x34440000 ori 4, 2, 0
• 0x00400028 0x34020004 ori 2, 0, 4 14
  ori v0, 0, 4
• 0x0040002c 0x012a4020 add 8, 9, 10 14
  add t0,t1,t2
• 0x00400030 0x0000000c syscall 15
  syscall
• 0x00400034 0x03e00008 jr 31 16
  jr ra

0 1 2 a 4 0 2 0
0000 0001 0010 1010 0100 0000 0010 0000
0 9 10 8
0 32
000000 01001 01010 01000 00000 100000
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What the hardware looks like.

• Multiplexors

Selector
Selector
Input bits
Outputs
0
0
Input
Output
31
31
The 5 selector wires can choose one of the 32
inputs voltages and send it to the output.
The 5 selector wires choose which of the 32
outputs will get the input voltage.
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What the hardware looks like.
This multiplexor is equivalent to 32 of those on
the previous page

• Multiplexors

Bit 0
Bit 31
Selector
Bit 0
Bit 31
Input words

0


Word 0
Output
Word 31
31
End View
End View
Side View
Now, each of the 32 inputs has 32 bits. There
are 32 x 32 bits in and 1 x 32 bits out.
Each of these input words COULD be a register!
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What the hardware looks like.

• ALU
• On this and the next few pages, we look at
  increasingly complicated forms of ALU.
• These pictures are taken from Figs 4.14, 4.17,
  4.18, 4.19 in the text.

A 1-bit ALU that performs AND, OR, and ADDITION.
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What the hardware looks like.

• ALU Continued

Causes set on Less operation.
A 1-bit ALU that performs AND, OR, and
ADDITION. The possible inputs are a, b, and b
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What the hardware looks like.

• ALU Continued

A 32-bit ALU that performs AND, OR, and
ADDITION. This is made up of 32 of the sub-pieces
weve just examined.
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What the hardware looks like.

• ALU Continued

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What the hardware looks like.

• Registers

Op
Select
5 wires
R0
6 wires
MUX To ALU
R8
A
B
MUX To ALU
ALU
c
ovf
Out
MUX From ALU
R31
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What the hardware looks like.
Op

• Registers

R0
MUX To ALU
R8
A
B
MUX To ALU
ALU
Out
MUX From ALU
R31
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The hardware reads each of those fields.
0 9 10
8 0 32
000000 01001 01010 01000 00000 100000

• Registers

R0
MUX To ALU
R8
A
B
MUX To ALU
ALU
Out
MUX From ALU
R31