Quantitative Analysis of Transaction Level Models for the AMBA Bus

The increasing complexity of embedded systems requires modeling at higher levels of abstraction. Transaction level modeling (TLM) has been proposed to abstract communication for high-speed system simulation and rapid design space exploration. Although being widely accepted for its high performance and efficiency, TLM often exhibits a significant loss in model accuracy. In this article, we systematically analyze and quantify the speed/accuracy trade-off in TLM. To this end, we provide a classification of TLM abstraction levels based on model granularity and define appropriate metrics and test setups to quantitatively measure and compare the performance and accuracy of such models. Addressing several classes of embedded communication protocols, we apply our analysis to three common bus architectures, the industry-standard AMBA advanced high-performance bus (AHB) as an on-chip parallel bus, the controller area network (CAN) as an off-chip serial bus, and the Motorola ColdFire Master Bus as an example for a custom embedded processor bus. Based on the analysis of these individual busses, we then generalize our results for a broader conclusion. The general TLM trade-off offers gains of up to four orders of magnitude in simulation speed, generally however, at the price of low accuracy. We conclude further that model granularity is the key to efficient TLM abstraction, and we identify conditions for accuracy of abstract models. As a result, this article provides general guidelines that allow the system designer to navigate the TLM trade-off effectively and choose the most suitable model for the given application with fast and accurate results.

This paper gives an overview of a transaction level modeling (TLM) design flow for the hardware architecture exploration with SystemC. TLM is widely used for hardware-software codesign, since the objective of TLM is the system exploration in the early stage of the design with fast but accurate simulation with abstracted transaction between modules in system. In this paper, we exploit the concept of TLM for the hardware architecture exploration. SystemC description methodology for TLM is described and the hardware architecture exploration of IEEE 802.11n PHY receiver is presented.

In recent years, transaction level modeling (TLM) has enabled designers to simulate complex embedded systems and SoCs, orders of magnitude faster than simulation at the RTL. The increasing complexity of the systems on one hand, and availability of low cost parallel processing resources on the other hand have motivated the development of parallel simulation environments for TLMs. The existing simulation environments used for parallel simulation of TLMs are intended for general discrete event models and do not take advantage of the specific properties of TLMs. The fine-grain synchronization and communication between simulators in these environments can become a major impediment to the efficiency of the simulation environment. In this work, we exploit the properties of temporally decoupled TLMs to increase the efficiency of parallel simulation. Our approach does not require a special simulation kernel. We have implemented a parallel TLM simulation framework based on the publicly available OSCI SystemC simulator. The framework is based on the communication interfaces proposed in the recent OSCI TLM 2 standard. Our experimental results show the reduced synchronization overhead and improved simulation performance.

SoC system designers commonly employ SystemC based Transaction level modeling (TLM) for its early software development usage and its analysis capabilities. TLM helps in realizing a SoC using virtual prototyping by integration of SoC components at different abstraction levels. The TLM 2 standard introduces interoperability rules for the models that may have been developed independently. However, neither SystemC compiler nor TLM library supports checking of such rules and manually debugging interoperability errors in such models could be a major problem. This provides motivation for developing automatic compliance checking techniques which can detect and report such errors. As the models are refined to incorporate detailed intercommunication protocols among the system components, the need for compliance checking extends to these protocols as well. In this paper, we present an efficient UML based compliance checking technique for TLM 2 models which supports static, dynamic and protocol-specific rule checking.

Transaction-level modeling (TLM) is the leading design style to deal with the increasing complexity of modern embedded systems. TLM provides designers with high-level interfaces and communication protocols for abstract modeling and efficient simulation of system platforms. The Open SystemC Initiative (OSCI) has recently released the TLM-2.0 standard for facilitating the interchange of models between suppliers and users, and thus encouraging the use of virtual platforms for fast simulation prior to the availability of register-transfer level (RTL) code. On the other hand, verification of TLM IPs still relies on simulation-based techniques since formal verification methodologies (such as model checking) and tools are not mature enough to be applied at TLM level. In this paper, we propose a methodology to apply existing RTL model checkers for verifying TLM IPs. The methodology relies on the automatic synthesis of the TLM IP models into equivalent RTL descriptions, in order to verify the TLM properties through the equivalent RTL model of the IPs.

The always increasing complexity of digital system is overcome in design flows based on transaction level modeling (TLM) by designing and verifying the system at different abstraction levels. The design implementation starts from a TLM high-level description and, following a top- down approach, it is refined towards a corresponding RTL model. However, the bottom-up approach is also adopted in the design flow when already existing RTL IPs are abstracted to be reused into the TLM system. In this context, proving the equivalence between a model and its refined or abstracted version is still an open problem. In fact, traditional equivalence definitions and formal equivalence checking methodologies presented in the literature cannot be applied due to the very different internal characteristics of the models, including structure organization and timing. Targeting this topic, the paper presents a formal definition of equivalence based on events, and then, it shows how such a definition can be used for proving the equivalence in the RTL vs. TLM context, without requiring timing or structural similarities between the modules to be compared. Finally, the paper presents a practical use of the proposed theory, by proving the correctness of a methodology that automatically abstracts RTL IPs towards TLM implementations.

An IP (Intellectual Property) based SoC (System-on-Chips) is getting popular among designers as it allows for a faster development cycle for SoC production. However, each IP may use different bus interface causing compatibility issues during design integration. A WISHBONE bus and an AHB (Advanced High Performance Bus) are among commonly used bus interfaces for many IP cores. This paper describes the conversion operation from WISHBONE Bus protocol into an AHB bus protocol. This is to allow an Open RISC Micro Controller Unit (ORMCU), a master device which uses WISHBONE bus protocols, to communicate and control all other devices (slaves) that use AHB bus protocols. The design is a WISHBONE-to-AHB Bridge, which consist of a WISHBONE slave and an AHB master inside one module. The simulation results confirm that the bridge is able to handle communication from a WISHBONE master in an AHB system.

Simulation is the most widely used form of validation using billions of random and pseudo-random tests in the traditional design flow. A critical problem in post-silicon debug is to generate efficient tests that both activate requisite coverage goal on the target hardware as well as produce results that are observable through a given on-chip design-for-debug architecture. Unfortunately, such tests cannot be generated directly from register-transfer level (RTL) models, both due to design complexity and due to bugs in the design itself. In this chapter, we discuss a directed test generation approach which facilities the observation of expected outputs of the generated tests using the traced signals. The proposed approach uses transaction-level models (TLM) for post-silicon test generation. The basic idea is to transform an RTL assertion as well as observability constraints to create a TLM assertion with observability constraints. The TLM assertion/property would be used to enable TLM analysis to generate post-silicon tests. Finally, the TLM test would be translated to an RTL test that is debug-friendly. In this chapter, we provide case studies from a number of different design classes to demonstrate the flexibility and effectiveness of the approach.

Efficient communication modeling is a critical task in SoC design and exploration. In particular, fast and accurate communication is needed to predict the performance of a system. Recently, Transaction Level Modeling (TLM) is used to speedup communication simulation at the cost of accuracy. This paper proposes a novel modeling technique called Result Oriented Modeling (ROM) which removes the accuracy drawback of TLM. Using ROM, models yield the same speed as their TLM counterparts, yet still are 100% accurate in timing. ROM utilizes the fact that internal states in the communication channel are not observable by the caller. Hence, ROM omits the internal states entirely and optimistically predicts the end result. Retroactively, the outcome is checked and, if necessary, corrective measures are taken to maintain the accuracy of the model. In this paper, we apply ROM to the AMBA AHB bus architecture. Our experimental results show that ROM exhibits the same high simulation performance as traditional TLM, yet it retains the same accuracy as the bus functional model. Thus, the proposed ROM approach eliminates the speed/accuracy tradeoff exhibited by traditional TLM.

VHDL as a hardware description language has some short-comings for system level modeling. Since previous researches [10] tried to extend this language for high level modeling, using Ada structures, and also it has derived some of its basic structures from Ada at first, we have decided to extend Ada to a form called SystemAda that can model hardware at transaction level modeling. Ada because of its intrinsic features like concurrency and object orientation can be a good candidate for a high level hardware modeling language. In our previous works we have proved that Ada can have a link to Register Transfer Level (RTL) and Transaction Level Modeling (TLM) modeling [3]. Here we have proofed the detailed characteristics of our TLM_FIFO channel -- just like the real TLM_FIFO -- and a way to TLM2.0 interfaces. Finally by simulation time comparison between SystemAda and SystemC TLM equivalent models we have proved that there is no simulation time penalty in SystemAda over SystemC.

This article presents a methodology for the design of Networked Embedded Systems (NESs), which extends Transaction Level Modeling (TLM) to perform system/network design-space exploration. As a result, a new design dimension is added to the traditional TLM refinement process to represent network configuration alternatives. Each network configuration can be used to drive both architecture exploration and system validation after each refinement step. A system/network simulation taxonomy is investigated aiming at precisely identifying the role of cosimulation in system/network design-space exploration. Furthermore, a general criterion to map functionalities to system and network models is presented. As a case study, the proposed methodology is applied to the design of a Voice-over-IP client.

Complex systems on chip (SoCs) present challenges in the design and verification process that cannot be adequately addressed by traditional methodologies based on register transfer descriptions. Some of the aspects are efficient design exploration based on component reuse, getting closure on the architecture, as well as early development, integration and verification of embedded software. In search for responses to these challenges, Transaction level modeling (TLM) has got quite some attention in the area of SoC design. This panel attempts to do a reality check on TLM from an engineering point of view. Questions to discuss are: Is the Transaction Level (TL) really useful for the design and/or for the verification of SoCs? How can TL speed up the design process and lowering the risk of design failures? What are the implications on tools, languages, and Intellectual Property (IP) used in the design/verification process? The panelists will share their thoughts on transaction based design and verification, and will discuss benefits and issues based on their experiences of applying transaction level methodologies.

This article presents the HeroeS virtual platform driven methodology for embedded multi-core and real-time SW design. The methodology's focus is on early integration, testing and performance estimation of heterogeneous SW stacks, i.e., SW components and layers at mixed abstraction levels and/or targeting different instruction sets. We take into account current system-level methodologies such as Transaction Level Modeling (TLM) and Real-Time Operating System (RTOS) modeling. For this, a SystemC virtual platform framework is presented combining state of the art simulation techniques according to the proposed methodology. This includes host-compiled target SW abstraction, abstract RTOS and Hardware Abstraction Layer (HAL) models in SystemC, extended QEMU user and system mode emulation and TLM 2.0 bus models. Efficient but yet accurate performance estimates can be provided through static and dynamic annotation. We apply binary mutation testing, i.e, a test assessment and improvement approach for instruction level SW testing. Our approach was investigated by prototypical integration into a commercial AUTOSAR environment. Experimental results were obtained by an automotive case study: a fault-tolerant fuel injection control system, which is part of an in-car network.

In this paper, we propose techniques for fast cycle-approximate multi-processor SoC simulation with timed transaction level models and OS models. Cycle-approximate simulation with an abstract model is widely used for fast validation of a multi-processor SoC in early design stages. However, the performance gain of abstract-level simulation is limited by the overhead of synchronizing multiple concurrent processor/module simulators, which is inevitable in timed simulation. To reduce the synchronization overhead, we adopt the synchronization time-point prediction method, which consists of two phases: static code analysis and dynamic scheduling of synchronizations. In the static analysis phase before simulation, it estimates minimum execution time from every point in the code to the nearest synchronization point. Then, during simulation, it pessimistically predicts the synchronization time-points based on the estimates. The proposed approach targets fast cycle-approximate simulation of a system with delay annotated SW code and transaction level models of HW with dynamic behavior. We present, in this paper, techniques to analyze such abstract models of SW and HW and schedule minimal number synchronizations during cycle-approximate simulation of the models. Experiments show that the approach achieves orders of magnitude higher performance in cycle-approximate multi-processor SoC simulation.

In this paper the authors present some key concepts concerning the specification language (PSL) utilization in a system level verification flow for system on chip (SoC) designs. As transaction level modeling (TLM) is the de-facto reference model for SoC design flow, the authors evaluate PSL adoption in TLM context. How to save time and effort in the verification phase during system development steps and how to overcome global system verification limitations through a compositional approach are discussed. Two PSL-based techniques, properties re-use and properties refinement, are described and compared in terms of refinement effort and simulation speed delay