Hector Posadas

Systematic embedded software generation from SystemC

The embedded software design cost represents an important percentage of the embedded-system development costs [1]. This paper presents a method for systematic embedded software generation that reduces the software generation cost in a platform-based HW/SW codesign methodology for embedded systems based on SystemC. The goal is that the same SystemC code allows system-level specification and verification, and, after SW/HW partition, SW/HW co-simulation and embedded software generation. The C++ code for the SW partition (processes and process communication including HW/SW interfaces) is systematically generated including the user-selected embedded OS (e.g.: the eCos open source OS).

RTOS modeling in SystemC for real-time embedded SW simulation: A POSIX model

SystemC is committed to support the requirements for an integrated, HW/SW co-design flow, thus allowing the development of complex, multiprocessing, Systems-on Chip (MpSoC). To make this possible, efficient modeling and simulation methodologies for Real-Time, Embedded (RT/E) SW in SystemC have to be developed, so that the designer can verify and refine the application SW together with the rest of the elements of the platform. Accurate modeling of the application SW requires an accurate model of the RTOS. Nevertheless, low-level, dynamic timing characteristics of the RTOS such as time-slicing, priority-based preemptive scheduling, interrupts and exceptions do not have a direct implementation in SystemC.In this paper, techniques are proposed to accurately model the detailed RTOS functionality on top of the SystemC execution kernel. The model allows timed-simulation and refinement of the RT/E SW code in SystemC. The simulation technology has been applied to the development of a high-level, POSIX simulation library in SystemC. The library allows the designer a fast, sufficiently accurate, timed simulation of the application SW running on top of POSIX. As most current RTOSs support this standard, the library is portable to different development frameworks. The library provides the required infrastructure for a complete, multiprocessing, HW/SW co-simulation environment at different abstraction levels using SystemC.

System-level performance analysis in SystemC

As both the ITRS and the Medea+ DA Roadmaps have highlighted, early performance estimation is an essential step in any SoC design methodology based on International Technology Roadmap for Semiconductors (2001) and The MEDEA+ Design Automation Roadmap (2002). This paper presents a C++ library for timing estimation at system level. The library is based on a general and systematic methodology that takes as input the original SystemC source code without any modification and provides the estimation parameters by simply including the library within a usual simulation. As a consequence, the same models of computation used during system design are preserved and all simulation conditions are maintained. The method exploits the advantages of dynamic analysis, that is, easy management of unpredictable data-dependent conditions and computational efficiency compared with other alternatives (ISS or RT simulation, without the need for SW generation and compilation and HW synthesis). Results obtained on several examples show the accuracy of the method. In addition to the fundamental parameters needed for system-level design exploration, the proposed methodology allows the designer to include capture points at any place in the code. The user can process the corresponding captured events for unrestricted timing constraint verification.

MULTICUBE: Multi-objective Design Space Exploration of Multi-core Architectures

Technology trends enable the integration of many processor cores in a System-on-Chip (SoC). In these complex architectures, several architectural parameters can be tuned to find the best trade-off in terms of multiple metrics such as energy and delay. The main goal of the MULTICUBE project consists of the definition of an automatic Design Space Exploration framework to support the design of next generation many-core architectures.

POSIX modeling in SystemC

Early estimation of the execution time of real-time embedded SW is an essential task in complex, HW/SW embedded system design. Application SW execution time estimation requires taking into account the impact of the underlying RTOS. As a consequence, RTOS modeling is becoming an active research area. SystemC provides a framework for multiprocessing, HW/SW co-simulation at several abstraction levels. In this paper, a SystemC library for POSIX modeling and simulation is presented. By using the library, the SystemC specification using POSIX functions is converted automatically into a timed simulation estimating the execution time of the application SW running on the POSIX platform. The library works directly on the source code. Therefore, it provides an early and fast estimation of the performance of the system as a consequence of the architectural mapping decisions. Although accuracy is lower than when using lower-level techniques, it supports high-level design-space exploration as simulation time is significantly less than RT (ISS) simulation.

The COMPLEX methodology for UML/MARTE Modeling and design space exploration of embedded systems

The design of embedded systems is being challenged by their growing complexity and tight performance requirements. This paper presents the COMPLEX UML/MARTE Design Space Exploration methodology, an approach based on a novel combination of Model Driven Engineering (MDE), Electronic System Level (ESL) and design exploration technologies. The proposed framework enables capturing the set of possible design solutions, that is, the design space, in an abstract, standard and graphical way by relying on UML and the standard MARTE profile. From that UML/MARTE based model, the automated generation framework proposed produces an executable, configurable and fast performance model which includes functional code of the application components. This generated model integrates an XML-based interface for communication with the tool which steers the exploration. This way, the DSE loop iterations are efficiently performed, without user intervention, avoiding slow manual editions, or regeneration of the performance model. The novel DSE suited modelling features of the methodology are shown in detail. The paper also presents the performance model generation framework, including the enhancements with regard the previous simulation and estimation technology, and the exploration technology. The paper uses an EFR vocoder system example for showing the methodology and for demonstrative results.

Platform based on open-source cores for industrial applications

The latest version of the international technology roadmap for semiconductors predicts that design reuse will be essential in the near future to face the constantly increasing design complexity. The concept comes from software engineering in which reuse is a fundamental technology. In order to provide libraries and applications to reuse in software development, some open-source initiatives (e.g. Linux, gcc, X, mysql) have appeared during the last decades. The basic idea is to distribute the library or application source code (normally free-of-charge) and allow any developer to use, modify, debug and improve it. Several initiatives have tried to port this idea to hardware development. The main goal of this paper is to develop a synthesizable platform described in SystemC from an open architecture. The platform includes a CPU (OpenRISC) and some basic peripherals. A set of software development tools (compiler, assembler, debugger) and RTOS (eCos) has also been developed. This work enables the evaluation of the advantages and disadvantages of the open-source model in electronic system design.

Fast data-cache modeling for native co-simulation

Efficient design of large multiprocessor embedded systems requires fast, early performance modeling techniques. Native co-simulation has been proposed as a fast solution for evaluating systems in early design steps. Annotated SW execution can be performed in conjunction with a virtual model of the HW platform to generate a complete system simulation. To obtain sufficiently accurate performance estimations, the effect of all the system components, as processor caches, must be considered. ISS-based cache models slow down the simulation speed, greatly reducing the efficiency of native-based co-simulations. To solve the problem, cache modeling techniques for fast native co-simulation have been proposed, but only considering instruction-caches. In this paper, a fast technique for datacache modeling is presented, together with the instrumentation required for its application in native execution. The model allows the designer to obtain cache hit/miss rate estimations with a speed-up of two orders of magnitude with respect to ISS. Miss rate estimation error remains below 5% for representative examples.

Single Source Design Environment for Embedded Systems Based on SystemC

There is a clear need for new methodologies supporting efficient design of embedded systems on complex platforms implementing both hardware and software modules. Software development has to be carried out under a closer relationship with the underlying platform. The current trend is towards an increasing embedded software development effort under more stringent time-to-market requirements. As a consequence, it is necessary to reduce software generation cost while maintaining reliability and design quality.In that context, languages centered on describing whole systems, with software and hardware parts, have been proposed. Among these, SystemC is gaining increasing interest as a specification language for embedded systems. SystemC supports the specification of the complete system and the modeling of the platform. In this paper, the application of SystemC to performance analysis and embedded software generation is discussed. A single-source approach is proposed, that is, the use of the same code for system-level specification and profiling, and, after architectural mapping, for HW/SW co-simulation and embedded software generation. A design environment based on C++ libraries for performance analysis and software generation is presented. This approach avoids working on intermediate formats and translators, which facilitates the designer’s interaction with the system description throughout the development process. Additionally, it ensures the preservation of the computational models used for the system specification during architectural mapping and compilation.

Fast instruction cache modeling for approximate timed HW/SW co-simulation

Approximate timed co-simulation has been proposed as a fast solution for system modeling in early design steps. This co-simulation technique enables the simulation of systems at speeds close to functional execution, while considering timing effects. As a consequence, system performance estimations can be obtained early, enabling efficient design space exploration and system refinement. To achieve fast simulation speeds, first the SW code is pre-annotated with time information and then it is natively executed, performing what is called native-based co-simulation. To obtain sufficiently accurate performance estimations, the effect of the system components must be considered. Among them, processor caches are really important, as they have a strong impact on the overall system performance. However, no efficient techniques for cache modeling in native-based co-simulation have been proposed. Previous works considering caches apply slow cache models based on tag search, similar to ISS-based models. This solution slows down the simulation speed, greatly reducing the efficiency of native based co-simulations. In this paper, a high-level instruction cache model is proposed, along with the required instrumentation for native simulation. This model allows the designer to obtain cache hit/miss rate estimations with simulation speeds very close to native execution. Results present a speed-up of two orders of magnitude with respect to ISS and one order of magnitude regarding previous approaches in native simulation. Miss rate estimation error remains below 5%.