AN2121 Freescale Semiconductor / Motorola, AN2121 Datasheet - Page 27

• Manufacturer Part Number: AN2121
• Description: JPEG2000 Arithmetic Encoding on StarCore SC140
• Manufacturer: Freescale Semiconductor / Motorola

Freescale Semiconductor, Inc.
StarCore Implementation in Assembler
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Summary
The arithmetic encoder C code given in Appendix A takes 4.6M cycles to complete one typical 128
128
pixel grey scale image, which corresponds to a processing time of 2 seconds to complete a color
1 megapixel image. This processing time has been measured with the assumption that the pixels are all
12 bits in size. In addition, it has been assumed that the StarCore processor is operating at a clock speed of
300 MHz. While the C code in Appendix A is ANSI C compliant, it was fully optimized by the StarCore
compiler to produce the given performance figures.
An optimized assembler version of the encoder codes the same grey scale image in less than one third of
the time taken by the C version. This increase in speed is due primarily to the arithmetic and multiplicity of
the address registers. StarCore’s parallel decision instructions and delayed change of flow instructions also
contributed to the improvement.
The DSP56307 (running at 100 MHz) encoded a constant grey scale image about 17 times more slowly
than the optimized assembler version using StarCore (running at 300 MHz).
Modifying the code to work with any image size should be fairly straightforward. All results were obtained
using the Beta 1.1 version of the StarCore software.
Summary
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