Section: Research Program

Virtual Prototyping

Virtual Prototyping is the technology of developing realistic simulators from models of a system under design; that is, an emulated device that captures most, if not all, of the required properties of the real system, based on its specifications. A virtual prototype should be run and tested like the real device. Ideally, the real application software would be run on the virtual prototyping platform and produce the same results as the real device with the same sequence of outputs and reported performance measurements. This may be true to some extent only. Some trade-offs have often to be made between the accuracy of the virtual prototype, and time to develop accurate models.

A virtual prototyping platform must include operating system or hardware emulation technology since the hardware functions must be simulated at least to a minimum extent in order to run the software and evaluate the design alternatives. The hardware simulation engine is a key component of a virtual prototyping platform, which makes it possible to run the application software and produce output that can be analysed by other tools. Because electronic design tools (EDAs) simulate the hardware in every detail, it is possible to verify that the circuit operates properly and also to measure how many clock cycles will be required to achieve an operation. But because they simulate very low-level operations, simulation is much too slow to be usable for virtual prototyping. The authors of the FAST system (The fast methodology for high-speed SOC simulation. D. Chiou, et al. International conference on Computer-aided design. IEEE, 2007.) and SocLib project reports (Using binary translation in event driven simulation for fast and flexible MPSOC simulation. M. Gligor, N. Fournel, and F. Pétrot. In CODES+ISSS, IEEE, 2009.) speed-ups with a factor of several hundreds in a comparison between their cycle accurate simulator and their virtual prototyping framework. A factor of the order of 100 times faster than EDA tools is required for virtual prototyping.

In order to speed-up simulation time, the virtual prototype must trade-off with something. Depending upon the application designers goals, one may be interested in trading some loss of accuracy in exchange for simulation speed, which leads to constructing simulation models that focus on some design aspects and provide abstraction of others. A simulation model can provide an abstraction of the simulated hardware in three directions:

• Computation abstraction. A hardware component computes a high level function by carrying out a series of small steps executed by composing logical gates. In a virtual prototyping environment, it is often possible to compute the high level function directly by using the available computing resources on the simulation host machine, thus abstracting the hardware function.

• Communication abstraction. Hardware components communicate together using some wiring, and some protocol to transmit the data. Simulation of the communication and the particular protocol may be irrelevant for the purpose of virtual prototyping: communication can be abstracted into higher level data transmission functions.

• Timing Abstraction. In a cycle accurate simulator, there are multiple simulation tasks, and each task makes some progress on each clock cycle, but this is slowing down the simulation. In a virtual prototyping experiment, one may not need to so precise timing information: coarser time abstractions can be defined allowing for faster simulation.

The cornerstone of a virtual prototyping platform is the component that simulates the processor(s) of the platform, and its associated peripherals. Such simulation can be static or dynamic.