ch7_031102 - Embedded Systems Design: A Unified...

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1 Embedded Systems Design: A Unified Hardware/Software Introduction Chapter 7 Digital Camera Example
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2 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Outline Introduction to a simple digital camera Designer’s perspective Requirements specification Design Four implementations
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3 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Putting it all together General-purpose processor Single-purpose processor Custom Standard Memory Interfacing Knowledge applied to designing a simple digital camera General-purpose vs. single-purpose processors Partitioning of functionality among different processor types Introduction
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4 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Introduction to a simple digital camera Captures images Stores images in digital format No film Multiple images stored in camera Number depends on amount of memory and bits used per image Downloads images to PC Only recently possible Systems-on-a-chip Multiple processors and memories on one IC High-capacity flash memory Very simple description used for example Many more features with real digital camera Variable size images, image deletion, digital stretching, zooming in and out, etc.
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5 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Designer’s perspective Two key tasks Processing images and storing in memory When shutter pressed: Image captured Converted to digital form by charge-coupled device (CCD) Compressed and archived in internal memory Uploading images to PC Digital camera attached to PC Special software commands camera to transmit archived images serially
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6 Embedded Systems Design: A Unified Hardware/Software Introduction, (c) 2000 Vahid/Givargis Charge-coupled device (CCD) Special sensor that captures an image Light-sensitive silicon solid-state device composed of many cells When exposed to light, each cell becomes electrically charged. This charge can then be converted to a 8-bit value where 0 represents no exposure while 255 represents very intense exposure of that cell to light. Some of the columns are covered with a black strip of paint. The light-intensity of these pixels is used for zero- bias adjustments of all the cells. The electromechanical shutter is activated to expose the cells to light for a brief moment. The electronic circuitry, when commanded, discharges the cells, activates the electromechanical shutter, and then reads the 8-bit charge value of each cell. These values can be clocked
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ch7_031102 - Embedded Systems Design: A Unified...

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