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Chapter 2: Custom single-purpose processors - page 20 / 29

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Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis

We often start with a state machine

Rather than algorithm

Cycle timing often too central to functionality

Example

Bus bridge that converts 4-bit bus to 8-bit bus

Start with FSMD

Known as register-transfer (RT) level

Exercise: complete the design

RT-level custom single-purpose processor design

Bridge

A single-purpose processor that converts two 4-bit inputs, arriving one at a time over data_in along with a rdy_in pulse, into one 8-bit output on data_out along with a rdy_out pulse.

data_in(4)

rdy_in

rdy_out

data_out(8)

clock

WaitFirst4

RecFirst4Start

data_lo=data_in

WaitSecond4

rdy_in=1

rdy_in=0

RecFirst4End

rdy_in=1

RecSecond4Start

data_hi=data_in

RecSecond4End

rdy_in=1

rdy_in=0

rdy_in=1

rdy_in=0

Send8Start

data_out=data_hi & data_lo

rdy_out=1

Send8End

rdy_out=0

Bridge

rdy_in=0

Inputs

 rdy_in: bit; data_in: bit[4];

Outputs

 rdy_out: bit; data_out:bit[8]

Variables

 data_lo, data_hi: bit[4];

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