Ericsson Radio Systems, a research and development group servicing the global Ericsson organization, develops strategic microelectronics for use in the company’s telecommunications products. Its solutions for cellular basestations were initially built around standard DSPs, which were later replaced by hardwired processors. However, because the standard DSP approach provided limited integration, and the hardwired solution lacked flexibility, Ericsson now designs its own custom DSP cores for this application. As many as ten of these cores are integrated into a single ASIC, where they share on-chip program and data memories to optimize silicon utilization. In the longer term, they plan to incorporate even more DSP cores into each ASIC.

Because the microelectronics group within Ericsson Radio Systems provides other Ericsson companies with enabling technologies rather than specific application solutions, it needs to supply its DSP cores with easy-to-use yet efficient high-level language compilers. On-chip memory constraints demand the use of compact code to drive the DSPs, but hand-crafting this code in assembler is not an acceptable long-term solution because it is both time consuming and imposes severe limitations on IP re-use. For Ericsson Radio Systems, the only answer was to have high-level language compilers specifically oriented to DSP applications.

"We chose ACE's CoSy compiler development system for two main reasons. First, because it looked quite easy to use, and second, because benchmarks indicated that compilers generated by CoSy produced very efficient DSP code." Magnus Jacobsson, Manager of DSP core development, Ericsson Radio Systems

Within two days of installing the CoSy software, Ericsson Radio Systems' engineers had modified a sample CoSy compiler and were generating executable code for their DSP cores. Within 12 months, validated compilers were available for the company's product development groups to generate control code for their target applications. Over the last year, the company has been developing optimizers that will enable the code generated by the final compilers to meet both the real-time execution requirements of telecom-oriented DSP algorithms and the memory constraints of the company's ASIC solutions.

Ericsson Radio Systems was one of the first companies to use CoSy-DSP, a version of ACE's CoSy compiler development system that includes special C language extensions to cope with the fixed-point arithmetic and divided memory spaces that are characteristic of embedded DSP cores. In addition to these new DSP-C language constructs, CoSy's modularity has proved invaluable in customizing Ericsson's compilers for DSP intensive applications. CoSy also makes it relatively easy to introduce new optimizers and code generators, and to mix and match them in a 'plug-and-play' type environment. This allows Ericsson's engineers to experiment with a wide range of different optimization strategies.

Ericsson Radio Systems is also benefiting from CoSy's ability to exploit the parallelism of its DSP cores during these optimizations. "Each of our cores is made up of several execution units that can be operated in parallel by freely assembling simple instructions into much longer instruction words," explained Jacobsson, "We are particularly impressed that CoSy can handle this parallelism one hundred percent," he added.

In the 18 months since it was installed, CoSy has enabled a company with enormous expertise in digital signal processing, but little experience in compiler development, to produce a powerful set of design tools that its application engineers can use to develop the next generation of mobile communication systems. By allowing the efficiency and portability of high-level language programming to be applied to areas once dominated by hand-written code, these tools will accelerate the launch of new multimedia services that will add features such as video telephony, web-browsing and e-mail facilities to mobile communications.