Last month, BDTI published the first independent, in-depth report to evaluate the ARM7, ARM9, and ARM9E processor cores. The ARM7 and ARM9 were not designed with the needs of DSP in mind, and these processors have no DSP-oriented features. Not surprisingly, BDTI's analysis shows that the ARM7 and ARM9 are not nearly as fast as mainstream DSP processors; for example, the 160 MHz Texas Instruments TMS320C54xx is about two times faster on DSP tasks than the 200 MHz ARM9.
The ARM9E—an ARM9 with DSP-oriented enhancements—offers significantly better DSP performance than the ARM7 and ARM9. According to BDTI's analysis, the 200 MHz ARM9E is about 70% faster than the 200 MHz ARM9 on 16-bit DSP tasks and about 15% slower than the 160 MHz TMS320C54xx. This level of performance may surprise some—the ARM9E DSP enhancements are fairly modest compared to those found in many other DSP-enhanced general-purpose processors.
Although the performance of the ARM9E is comparable to that of older DSP-oriented processors, it is far slower than newer DSP-oriented processors. According to BDTI's analysis, the successor to the TMS320C54xx, the 200 MHz Texas Instruments TMS320C55xx, is over two times faster than the 200 MHz ARM9E. This performance gap is largely due to a difference in MAC throughput: nearly all recent DSP-oriented architectures—including DSP-enhanced general-purpose processors— support two (or more) MACs per cycle, but the ARM cores are limited to only one multiply-accumulate per cycle. ARM seems to be aware of this shortcoming: in October 2001 ARM revealed that its next-generation core will include a dual-MAC SIMD operation.
Despite their modest speed, the ARM7 and ARM9 cores have already found success in several DSP applications with modest computational requirements. For example, many portable digital audio players rely on ARM7 cores. ARM cores are also used in many applications that currently require both a general-purpose processor and a DSP. With its improved DSP performance, the ARM9E may eliminate the need for a separate DSP in some of these applications.
Performance is only one of many factors that determine whether a core will be successful. One of the key reasons for ARM's success is the quality and quantity of the development tools and the software available for ARM cores, which is in turn largely due to ARM's strong track record of compatibility. In addition, ARM-based off-the-shelf chips are available from a number of vendors. Thus, potential licensees have the ability to develop initial system designs using off-the-shelf chip-level products, then migrate to an SoC design when volumes justify the additional costs. And unlike some licensable cores, the ARM cores have been proven in silicon again and again, making them a less risky choice than less established cores.