This month Analog Devices introduced the ADSP-21375, the newest member of its SHARC floating-point DSP family. The new chip will operate at 266 MHz and be priced at $5 in high volumes ($7.95 in 10K quantities). It will target consumer audio applications and cost-sensitive application areas traditionally dominated by low cost fixed-point DSPs, including industrial, automotive, medical and instrumentation applications.
The ‘21375 will be pin-compatible with the existing ADSP-21367/8/9 SHARC processors. The major architectural difference between the ‘21375 and its pin-compatible family members is a 4X reduction of on-chip RAM from 256 Kbytes to 64 Kbytes and a 3X reduction in ROM from 750 KBytes to 256 KBytes. To help compensate for the much smaller on-chip memories, ADI added the ability to execute code from external SDRAM at the expense of slower execution time. (The maximum instruction execution rate is reduced by 8X when executing instructions from external memory.) In addition, the ‘21375 will have a lower maximum clock frequency than existing SHARC chips, which operate at up to 400 MHz.
In comparison with other floating-point processors, the main advantage of the ‘21375 is its low cost. For example, the least expensive existing SHARC processor, the 150 MHz ‘21261, is priced at $9.95. The ‘21375 is also about 80% faster than the ‘21261.
The ‘21375 is also less expensive than competing floating-point processors. For example, the least expensive floating-point processor from Texas Instruments, the 200 MHz TMS320C6722, is also priced at $9.95. BDTI Benchmark scores are not yet available for the ‘C6722, but BDTI estimates that the ‘C6722 will be slower than the ‘21375 on signal-processing tasks. Of course, the extra cost and decrease in performance associated with off-chip memory, if needed, must be taken into account.
In comparison with low-cost, 16-bit fixed-point DSPs, a floating-point processor can be appealing because of its higher numeric fidelity and lower software development effort. On the other hand, floating-point processors are less energy efficient and tend to have larger memory footprints. For example, Analog Devices’ own Blackfin family of fixed-point processors includes a chip priced at $4.95. An analysis of BDTI Benchmark results shows that the ‘21375 uses about twice as much memory as this Blackfin processor. (Benchmark scores for these chips are available at http://www.BDTI.com/Services/Benchmarks .)
The ‘21375 will be uniquely inexpensive among floating-point processors. Its low cost creates interesting possibilities for the use of floating-point chips in cost-sensitive applications. However, system designers should be aware that this new processor continues in the SHARC family tradition of being audio oriented, with peripherals and tools geared towards audio applications. It should also be noted that industrial and automotive grade packages are being considered, but the ‘21375 will initially be available only in a commercial grade package.
Samples of the ‘21375 are expected to be available in the second quarter 2006 and full production is expected in the fourth quarter of 2006.
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