SANTA CLARA, Calif. Bucking convention, National Semiconductor Corp. has chosen Tensilica Inc.'s configurable processor to serve as the digital baseband in a high-speed chip set for wireless-service provider Metricom Inc.
The chip set will provide the processing horsepower to allow Metricom, known for its Ricochet wireless service, to double its current transmission speed to 256 kbits/second by using customized signal-processing algorithms being developed by National and Metricom for execution on Tensilica's Xtensa III core.
"Metricom felt they needed to have something above 120 Mips of DSP performance," said Pat Sullivan, product line manager for National's custom-solutions division, which oversees CPU architectures. "National does have some internal solutions, but none of them could achieve that."
After evaluating Tensilica's configurable architecture, National determined it could develop an integrated CPU and DSP digital baseband d evice that can exceed 160 Mips. National engineers are now in the process of finalizing the architecture and writing the digital-processing instruction extensions, known as Tensilica Instruction Extensions (TIEs).
At the same time, the company is defining peripheral blocks that will go around the core, such as UARTs and interfaces like PCI, USB and PCMCIA. The device will also contain a large chunk of internal SRAM so it can approach an operating frequency of 200 MHz, something that wouldn't be possible using off-chip memory. The company has not yet decided what kind of on-chip bus it will use, Sullivan said.
"It's a complex architecture," Sullivan said. "Obviously there's lots of things to monitor and control, and we knew we needed a combination of a CPU and DSP. One way is to put a separate DSP and CPU on the same chip. In this case, the CPU is the DSP and the DSP is the CPU."
For Tensilica, the deal between National and Metricom could be a stepping stone for gaining acceptance in wireless devi ces, such as third-generation cellular phones. Traditionally, mobile phones use a tightly coupled CPU and DSP, but many observers believe there will be room for additional processing.
National, for its part, had looked into developing a configurable CPU itself, but in the end chose to use Tensilica because that company had a working solution that could be introduced to the marketplace sooner.