Towards Equivalence Checking Between TLM and RTL Models

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.

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.

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.

Mutation analysis is a widely-adopted strategy in software testing with two main purposes: measuring the quality of test suites, and identifying redundant code in programs. Similar approaches are applied in hardware verification and testing too, especially at RTL or gate level, where mutants are generally referred as faults, and mutation analysis is performed by means of fault modeling and fault simulation. However, in modern embedded systems there is a close integration between HW and SW parts, and verification strategies should be applied early in the design flow. This requires the definition of new mutation analysis-based strategies that work at system level, where HW and SW functionalities are not partitioned yet. In this context, the paper proposes a mutation model for perturbing transaction level modeling (TLM) SystemC descriptions. In particular, the main constructs provided by the SystemC TLM 2.0 library have been analyzed, and a set of mutants is proposed to perturb the primitives related to the TLM communication interfaces.

Currently, system-on-chip (SoC) designs are becoming increasingly complex, with more and more components being integrated into a single SoC design. Communication between these components is increasingly dominating critical system paths and frequently becomes the source of performance bottlenecks. It, therefore, becomes imperative for designers to explore the communication space early in the design flow. Traditionally, system designers have used Pin-Accurate Bus Cycle Accurate (PA-BCA) models for early communication space exploration. These models capture all of the bus signals and strictly maintain cycle accuracy, which is useful for reliable performance exploration but results in slow simulation speeds for complex, designs, even when they are modeled using high-level languages. Recently, there have been several efforts to use the Transaction-Level Modeling (TLM) paradigm for improving simulation performance in BCA models. However, these transaction-based BCA (T-BCA) models capture a lot of details that can be eliminated when exploring communication architectures. In this paper, we extend the TLM approach and propose a new transaction-based modeling abstraction level (CCATB) to explore the communication design space. Our abstraction level bridges the gap between the TLM and BCA levels, and yields an average performance speedup of 120% over PA-BCA and 67% over T-BCA models, on average. The CCATB models are not only faster to simulate, but also extremely accurate and take less time to model compared to both T-BCA and PA-BCA models. We describe the mechanisms that produce the speedup in CCATB models and also analyze how the achieved simulation speedup scales with design complexity. To demonstrate the effectiveness of using CCATB for exploration, we present communication space exploration case studies from the broadband communication and multimedia application domains.

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

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.

With power becoming a major constraint for multi-processor embedded systems, it is becoming important for designers to characterize and model processor power dissipation. It is critical for these processor power models to be useable across various modeling abstractions in an electronic system level (ESL) design flow, to guide early design decisions. In this paper, we propose a unified processor power modeling methodology for the creation of power models at multiple granularity levels that can be quickly mapped to an ESL design flow. Our experimental results based on applying the proposed methodology on an OpenRISC processor demonstrate the usefulness of having multiple power models. The generated models range from very high-level two-state and architectural/ISS models that can be used in transaction level models (TLM), to extremely detailed cycle-accurate models that enable early exploration of power optimization techniques. These models offer a designer tremendous flexibility to trade off estimation accuracy with estimation/simulation effort.

With power becoming a major constraint for multiprocessor embedded systems, it is becoming important for designers to characterize and model processor power dissipation. It is critical for these processor power models to be useable across various modeling abstractions in an electronic system level (ESL) design flow, to guide early design decisions. In this paper, we propose a unified processor power modeling methodology for the creation of power models at multiple granularity levels that can be quickly mapped to an ESL design flow. Our experimental results based on applying the proposed methodology on the OpenRISC and MIPS processors demonstrate the usefulness of having multiple power models. The generated models range from very high-level two-state and architectural/instruction set simulator models that can be used in transaction level models, to extremely detailed cycle-accurate models that enable early exploration of power optimization techniques. These models offer a designer tremendous flexibility to trade off estimation accuracy with estimation/simulation effort.

Transaction-level modeling (TLM) is the most promising technique to deal with the increasing complexity of modern embedded systems. However, modeling a complex system completely at transaction level could be inconvenient when IP cores are available on the market, since they are usually modeled at register transfer level (RTL). In this context, modeling and verification methodologies based on transactors allow designers to reuse RTL IPs into TLM-RTL mixed designs, thus guaranteeing a considerable saving of time. Practical advantages of such an approach are evident, but mixed TLM-RTL designs cannot completely provide the well-known effectiveness in terms of simulation speed provided by TLM. This paper presents a methodology to automatically abstract RTL IPs into equivalent TLM descriptions. To do that, the paper first proposes a formal definition of equivalence based on events, showing how such a definition can be applied to prove the correctness of a code manipulation methodology, such as code abstraction. Then, the paper proposes a technique to automatically abstract RTL IPs into TLM descriptions. Finally, the paper shows that the TLM descriptions obtained by applying the proposed technique are correct by construction, relying on the given definition of event-based equivalence. A set of experimental results is reported to confirm the effectiveness of the methodology.

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

The aim is to explain the current issues of HW/SW cosimulation and to introduce a new challenge of HW/SW cosimulation for multiprocessor SoC (MPSoC). Most of the current issues are related to raising abstraction levels of HW/SW cosimulation. Mixed-level cosimulation is explained in a unified manner using a concept of ‘HW/SW interface’. First, abstraction levels in HW/SW cosimulation are explained in terms of abstraction levels of function, SW interface and HW interface. Transaction level models are introduced for HW interface. OS and device driver levels are explained for the SW interface. Then, the concept, applications and techniques of mixed-level cosimulation are presented. To better understand mixed-level cosimulation through SoC design flow, a view called refinement space is presented. Using the refinement space, cases of mixed-level cosimulation are explained in a SoC design scenario. Then, the issue of cosimulation performance in raising abstraction levels, i.e. Amdahl's law in HW/SW cosimulation, is addressed. A new challenge of cosimulation for MPSoC is also introduced.

Increasing system complexity and heterogeneity make system integration and communication synthesis a growing concern. Even with transaction-level modeling and high-level synthesis of hardware, communication interfaces still have to be manually designed at a low protocol level.To address this challenge, we present a design flow for automatic synthesis of hardware transactors, which realize abstractly specified communication semantics on top of protocol-level transactions. Transactor synthesis is tightly coupled with high-level synthesis of computation for integrated computation/communication co-design of complete hardware processors, thus establishing a seamless path from abstract system specifications down to hardware implementations in synthesizable RTL. The flow supports a generic set of communication semantics and target implementations, where transactors are custom-generated for a specific application and architecture combination. Furthermore, we develop protocol stack optimizations that reduce the area and performance overhead of synthesized communication interfaces. We have applied our synthesis flow to several industrial-strength examples under various communication settings. Results show that synthesized interfaces are comparable to manual designs in terms of area and latency, where protocol stack optimizations can reduce area and latency overhead by up to 77% and 21%, respectively.

Different techniques and commercial tools are at the state of the art to reuse existing RTL IP implementations to generate more abstract (i.e., TLM) IP models for system-level design. In contrast, reusing, at TLM, an assertion-based verification (ABV) environment originally developed for an RTL IP is still an open problem. The lack of an effective and efficient solution forces verification engineers to shoulder a time consuming and error-prone manual re-definition, at TLM, of existing assertion libraries. This paper is intended to fill in the gap by presenting a technique to automatically abstract properties defined for RTL IPs with the aim of creating dynamic ABV environments for the corresponding TLM models.

Different techniques and commercial tools are at the state of the art to reuse existing RTL IP implementations to generate more abstract (i.e., TLM) IP models for systemlevel design. In contrast, reusing, at TLM, an assertion-based verification (ABV) environment originally developed for an RTL IP is still an open problem. The lack of an effective and efficient solution forces verification engineers to shoulder a time consuming and error-prone manual re-definition, at TLM, of existing assertion libraries. This paper is intended to fill in the gap by presenting a technique to automatically abstract properties defined for RTL IPs with the aim of creating dynamic ABV environments for the corresponding TLM models.