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A Prototype Optical Tracking System Investigation and Development - page 74 / 170

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Black Spot Hardware

Blackfin BF533 of 132 M bytes.

5.3.2

Estimate of required processing capabilities

It was difficult to accurately predict the computational requirements of the camera mod- ule, however, a rough estimate of the bare minimum processing power was useful during design. The most intensive part of the firmware is calculating the centroid of a ROI. 32 by 32 pixel ROI contains 1024 pixels that need to be processed. In Chapter 4 it is estimated that this requires approximately 41.5 Mips (Equation 4.2). The Blackfin BF533 can operate

at up to 600 M Hz giving a total of 600 Mips. The device also allows execution of two 16 bit instructions in parallel with one 32 bit instruction under some circumstances. Optimisation of the centroid algorithm to use efficient instructions on the Blackfin could also increase the processor’s performance. Clearly, as far as speed is concerned, the Blackfin is a good choice for this application.

5.3.3

Estimate of power requirements

n estimate of the power required for the main components of the module is given in Table

5.2. This is based on data found in the datasheets for the Blackfin BF53x family [80], image sensor [78], and linear regulator [81] and assumes the Blackfin is in its active state all of the time. The assumption that the Blackfin is active 100% of the time leads to a power estimate that represents a worst case scenario. s shown, the Blackfin and image sensor have similar power requirements. Using the current drawn by both these components the power dissipated by the 3.3 V linear voltage regulator on the board was calculated. This was calculated using the voltage drop between the 5 V supply and the 3.3 V regulator

output given by

PREG

= I R E G

( V I N

VOUT

),

(5.1)

and the current flowing through the regulator, i.e.,

IREG

= IDSP

  • +

    ISENSOR

.

(5.2)

This gives

IREG

= 240 + 97 = 337 mA

(5.3)

which leads to

PREG

= 0.337(5

3.3) 573 mW.

(5.4)

This is a large percentage of the power requirements and indicates using a more efficient switching regulator would be a good option.

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