Automatic Abstraction of RTL IPs into Equivalent TLM Descriptions

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.

Transaction level (TL) models are key to early design exploration, performance estimation and virtual prototyping. Their speed and accuracy enable early and rapid System-on-Chip (SoC) design evaluation and software development. Most devices have only register transfer level (RTL) models that are too complex for SoC simulation. Abstracting these models to TL ones, however, is a challenging task, especially when the RTL description is too obscure or not accessible. This work presents a methodology for automatically creating a TL model of an RTL memory controller component. The device is treated as a black box and a multitude of simulations is used to obtain results, showing its timing behavior. The results are classified into conditional probability distributions, which are reused within a TL model to approximate the RTL timing behavior. The presented method is very fast and highly accurate. The resulting TL model executes approximately 1200 times faster, with a maximum measured average timing offset error of 7.66%.

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.

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.

Transaction-level modeling is used in hardware design for describing designs at a higher level compared to the register-transfer level (RTL) (e.g. Cai and Gajski in CODES+ISSS '03: proceedings of the 1st IEEE/ACM/IFIP international conference on Hardware/software codesign and system synthesis, pp. 19---24, 2003; Chen et al. in FMCAD '07: proceedings of the formal methods in computer aided design, pp. 53---61, 2007; Mahajan et al. in MEMOCODE '07: proceedings of the 5th IEEE/ACM international conference on formal methods and models for codesign, pp. 123---132, 2007; Swan in DAC '06: proceedings of the 43rd annual conference on design automation, pp. 90---92, 2006). Each transaction represents a unit of work, which is also a useful unit for design verification. In such models, there are many properties of interest which involve interactions between multiple transactions. Examples of this are ordering relationships in sequential processing and hazard checking in pipelined circuits. Writing such properties on the RTL design requires significant expertise in understanding the higher-level computation being done in a given RTL design and possible instrumentation of the RTL to express the property of interest. This is a barrier to the easy use of such properties in RTL designs. In this paper, we consider specification of interaction properties at the transaction-level and the subsequent encoding of the property and the transaction-level model as a finite-state system for model checking. We discuss how the encoded finite-state system can be automatically generated from the specification of the property and the transaction-level model, and illustrate this through simple examples.

Early system modelling is an essential tool to accelerate software development, architectural analysis and hardware verification in complex many-core system-on-chips (SoCs). Transaction level modelling (TLM) offers a higher level of abstraction than register transfer level (RTL) and can be used for early system modelling. Maintaining simulation speed with the right accuracy is a major challenge and this paper proposes SystemC-based architectural modelling techniques that extend TLM to deliver faster simulation models for many-core system. The proposed approach considers a micro-scheduler for large modules (in the sense of SystemC modules) to locally manage all events in the module. Exploiting this micro-scheduler along with function object and coroutine concepts, the authors propose a lightweight thread process that significantly reduces the context switching overhead among the different processes. Additionally the micro-scheduler allows some processes to be run ahead of simulation time. The proposed techniques are applied to the model of a very large networks-on-chip (NoC) formed by thousands of cores stressing the simulation capabilities of the host computer and operating system. The experimental results demonstrate that the model can run successfully and exhibits up to 93% improvement in simulation speed compared to traditional SystemC-based modelling.

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.

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.

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.

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.

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.

Current hardware design and verification methodologies reflect a trend towards abstraction levels higher than RTL, referred to as transaction level (TL). Since transaction level models (TLMs) are used for early prototyping and as reference models for the verification of their RTL representation, the quality assurance of TLMs is vital. Assertion based verification (ABV) of RTL models has improved quality assurance of IP blocks and SoC systems to a great extent. Since mapping of an RTL ABV methodology to TL poses severe problems due to different design paradigms, current ABV approaches need extensions towards TL. In this paper we present a prototype implementation of a TL assertion framework using SystemC which is currently the de facto standard for system modeling

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.

The increasing complexity of embedded systems pushes system designers to higher levels of abstraction. Transaction Level Modeling (TLM) has been proposed to model communication in systems in an abstract manner. Although being widely accepted, TLMs have not been analyzed for their loss in accuracy. This paper will analyze and quantify the speed-accuracy tradeoff of TLM using a case study on AMBA, an industry bus standard. It shows the results of modeling the Advanced High-performance Bus (AHB) of AMBA using a set of models at different abstraction levels. The analysis of the simulation speed shows improvements of two orders of magnitude for each TLM abstraction, while the timing in the model remains accurate for many applications. As a result, the paper will classify the different models towards their applicability in typical modeling situations, allowing the system designer to achieve fast and accurate simulation of communication.

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.