Embedded Computing Design - OpenSystems Media

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Building the product The EDK hardware consists of the sensor, a processor, a boot Flash, and an SDRAM. The sensor can be connected to the processor with any number of serial interfaces. In this case, a UART was chosen in order to leave the SPI port open for host communications. A number of additional interface configurations are possible using an optional connector interface. The AFS8600 EDK block diagram is shown in Figure 3. The answer The answer came from an unlikely source. Analog Devices, Inc., which is traditionally known for its DSPs, has introduced the ADSP-BF531 as a new low cost member of its Blackfin family. The Blackfin performs microcontroller functions with dexterity comparable to its DSP functions. In this application, the ADSP-BF531 was essentially an inexpensive 800 MIPS microprocessor. The sensor side of the AFS8600 is shown in Figure 1, and the processor side is shown in Figure 2. Figure 3 Figure 1 The ADSP-BF531 has 32 Kbytes of internal code SRAM, and 20 Kbytes of internal data SRAM. If necessary, 16 Kbytes of internal code SRAM, and 16 Kbytes of internal data SRAM may be configured as cache instead. Because of the large size of the fingerprint matching library, nearly all of the code and data went into external SDRAM. The caches would have to perform extremely well in this circumstance, and they did not disappoint. Table 1 lists the average times for a one-to-one match. Note that the times are well below the 500 ms requirement. It should be noted that the core clock could be reduced to half of its peak rate, and still achieve the required match time. Because the Blackfin can lower its core voltage when the clock rate is reduced, this can result in a significant reduction to the Blackfin’s already low active power consumption. Core Clock Bus Clock Average Match Time 396 MHz 132 MHz 167 ms 198 MHz 132 MHz 336 ms Figure 2 Table 1 Validation To validate the match time results, a test was run on the Blackfin to compare its match scores to those obtained with the same matcher library running on a PC. This was accomplished with canned fingerprint images so that the enroll and verify images are identical. If the match scores computed on the embedded platform are identical to those on the PC, then there is confidence that there are no compiler bugs or idiosyncrasies in the embedded platform that would cause the matcher to malfunction or give incorrect results. The test was performed with two sets of five different canned images. The match scores from the Blackfin were identical bit-for-bit to those from the PC – a rare occurrence for an embedded processor. 50 / Summer 2004 Embedded Computing Design
“A number of additional interface configurations are possible using an optional connector interface.” years at Harris Semiconductor in various roles, including device engineering, process engineering, yield enhancement, engineering management, and marketing. Kasten holds a BSEE degree from the University of California, has three patents to his credit, and is fluent in several Asian languages. For further information, contact Alan at: AuthenTec, Inc. 709 S. Harbor City Blvd. • Melbourne, FL 32901 Tel: 321-308-1344 • Fax: 321-308-1430 E-mail: al.kasten@authentec.com • Website: www.authentec.com FingerLoc and TruePrint are registered trademarks of AuthenTec, Inc. Blackfin is a registered trademark of Analog Devices, Inc. Other brand or product names are registered trademarks or trademarks of the respective holders. Conclusion The excellent match accuracy of the AFS8600 combined with the 800 MIPS performance and low-cost of the ADSP- BF531 have made fingerprint biometrics viable for consumer market adoption. Kevin C. Kreitzer is a Senior Field Applications Engineer with Analog Devices, Inc. in St. Petersburg, Florida where he supports DSP and embedded processor products. He has Bachelor of Science and Master of Engineering degrees in Electrical Engineering from the University of Florida, specializing in DSP and Communications. Prior to joining Analog Devices in 2000, Kreitzer spent 11 years designing Software-Defined Radios with various defense contractors. For further information, contact Kevin at: Analog Devices, Inc. 5172 Venetian Blvd. N.E. St. Petersburg, FL 33703 Tel: 727-521-6614 E-mail: kevin.kreitzer@analog.com Website: www.analog.com Alan Kasten is an Applications Engineer with AuthenTec, Inc. in Melbourne, Florida. He helped to found AuthenTec when it was first spun-off from Harris Semiconductor in 1998, and has been with the Company ever since. Kasten worked for more than 20 RSC #51 @ www.embedded-computing.com/rsc Embedded Computing Design Summer 2004 / 51
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