As embodied in commercial DSP algorithm-development tools like HP EEsof's first generation Ptolemy (now called "Ptolemy Classic" by its developers), the tool offers designers a rapid-response way to examine the complex interaction of system-level elements. It provides behavioral modeling for hybrid systems combining embedded processors (some operating concurrently, some tightly sequenced) and DSPs as well as analog and mixed-signal devices.

The new Ptolemy uses a multithreaded kernel and a modular structure in which "actors" (finite states or complex computational routines) are interconnected by "signals" and "data flows." Combined with visualization tools (like graphical plotting mechanisms or browsers), it offers an improved framework for combining or calling diverse computational models — including logic simulators or finite state machines that model discrete events, and others like Spice that model conditions over a continuous time frame.

"We're trying to push the envelope for what the [modeling] tools can do," said Berkeley professor Edward Lee, Ptolemy's primary promoter, at the opening of a miniconference he organized here. "Ptolemy is an open architecture for people who want to experiment," he said.

Like the widely used MatLab simulator from The MathWorks (Natick, Mass.), first-generation Ptolemy has been harnessed for algorithm development. Both simulators allow designers to visualize the interactions of functional blocks (some with intensive mathematics processing) on a relatively high level of abstraction. Unlike MatLab, the Ptolemy design language is hierarchical, allowing components to be embedded within the system-level constructs. It thus allows easier mapping between system-level elements and lower-level ICs.

For example, the Sanders subsidiary of Lockheed Martin (Nashua, N.H.) used the Ptolemy modeling system in the construction of the company's Adaptive Computing System (ACS), a platform for DSP algorithm development. For any particular algorithmic function, the ACS environment allows engineers to analyze the impact of bit widths, latency and cell count on the performance of the system, said system design manager Eric Pauers in a miniconference presentation.

ACS is particularly adept at DSP floating-point to fixed-point translation, where engineers attempt to find the optimum hardware required to complete a particular computational operation. ACS helps engineers calculate the specific bit widths for each flow and provides "cost estimates" in terms of the silicon die area and complexity, and the trade-offs in terms of quantization noise and other design anomalies. In the Sanders tool set, Ptolemy links to a VHDL code generator. This enables designers to target Xilinx FPGAs and other ASIC devices for DSP operations.

Ptolemy Classic, in fact, formed the basis for the algorithm-development tools assembled and marketed by Hewlett-Packard's EEsof division (Westlake Village, Calif.). Jose Luis Pino, HP EEsof's staff scientist, was a member of the UC Berkeley Ptolemy group from 1990 to 1996, and led the effort to commercialize Ptolemy Classic. EEsof rewrote Ptolemy to make it run faster and smoother, said Khali Kalbasi, a member of HP's Technical Staff. The timed synchronous data-flow concept, embodied in Ptolemy, allows complex combinations of RF signals to be modeled without oversampling.

The Ptolemy engine, in addition, allows cosimulation of RF systems with harmonic balance simulators and other linear circuit-analysis tools. By presenting system elements (actors) on a relatively high level of abstraction, the EEsof platform thus simplifies the modeling complexity for the user. "Customers don't want to see intricacies of the model," said Kalbasi. The Ptolemy engine, however, allows simulation results to be presented in the frequency domain, or fine-grained in the time domain.

Ptolemy formed the basis of the fiber-optic simulation system developed by Virtual Photonics, which allows fiber-optic systems to be simulated on the HP EEsof platform. Ptolemy is also the basis of the wireless network simulator developed at Dresden's University of Technology. Synopsys' Cossap DSP development tools are also believed to have roots in Ptolemy Classic.