Formal Verification of a MESI-based Cache Implementation

Cache coherency is crucial to multi-core systems with a shared memory programming model. Coherency protocols have been formally verified at the architectural level with relative ease. However, several subtle issues creep into the hardware realization of cache in a multi-processor environment. The assumption, made in the abstract model, that state transitions are atomic, is invalid for the HDL implementation. Each transition is composed of many concurrent multi-core operations. As a result, even with a blocking bus, several transient states come into existence. Most modern processors optimize communication with a split-transaction bus, this results in further transient states and race conditions. Therefore, the design and verification of cache coherency is increasingly complex and challenging. Simulation techniques are insufficient to ensure memory consistency and the absence of deadlock, livelock, and starvation. At best, it is tediously complex and time consuming to reach confidence in functionality with simulation. Formal methods are ideally suited to identify the numerous race conditions and subtle failures. In this study, we perform formal property verification on the RTL of a multi-core level-1 cache design based on snooping MESI protocol. We demonstrate full-proof verification of the coherence module in JasperGold using complexity reduction techniques through parameterization. We verify that the assumptions needed to constrain inputs of the stand-alone cache coherence module are satisfied as valid assertions in the instantiation environment. We compare results obtained from formal property verification against a state-of-the-art UVM environment. We highlight the benefits of a synergistic collaboration between simulation and formal techniques. We present formal analysis as a generic toolkit with numerous usage models in the digital design process

High-level verification flow for a high-level synthesis-based digital logic design

Abstract. High-level synthesis (HLS) is a method for generating register-transfer level (RTL) hardware description of digital logic designs from high-level languages, such as C/C++/SystemC or MATLAB. The performance and productivity benefits of HLS stem from the untimed, high abstraction level input languages. Another advantage is that the design and verification can focus on the features and high-level architecture, instead of the low-level implementation details. The goal of this thesis was to define and implement a high-level verification (HLV) flow for an HLS design written in C++. The HLV flow takes advantage of the performance and productivity of C++ as opposed to hardware description languages (HDL) and minimises the required RTL verification work. The HLV flow was implemented in the case study of the thesis. The HLS design was verified in a C++ verification environment, and Catapult Coverage was used for pre-HLS coverage closure. Post-HLS verification and coverage closure were done in Universal Verification Methodology (UVM) environment. C++ tests used in the pre-HLS coverage closure were reimplemented in UVM, to get a high initial RTL coverage without manual RTL code analysis. The pre-HLS C++ design was implemented as a predictor into the UVM testbench to verify the equivalence of C++ versus RTL and to speed up post-HLS coverage closure. Results of the case study show that the HLV flow is feasible to implement in practice. The flow shows significant performance and productivity gains of verification in the C++ domain when compared to UVM. The UVM implementation of a somewhat incomplete set of pre-HLS tests and formal exclusions resulted in an initial post-HLS coverage of 96.90%. The C++ predictor implementation was a valuable tool in post-HLS coverage closure. A total of four weeks of coverage work in pre- and post-HLS phases was required to reach 99% RTL coverage. The total time does not include the time required to build both C++ and UVM verification environments.Korkean tason verifiointivuo korkean tason synteesiin perustuvalle digitaalilogiikkasuunnitelmalle. Tiivistelmä. Korkean tason synteesi (HLS) on menetelmä, jolla generoidaan rekisterisiirtotason (RTL) laitteistokuvausta digitaalisille logiikkasuunnitelmille käyttäen korkean tason ohjelmointikieliä, kuten C-pohjaisia kieliä tai MATLAB:ia. HLS:n suorituskykyyn ja tuottavuuteen liittyvät hyödyt perustuvat ohjelmointikielien tarjoamaan korkeampaan abstraktiotasoon. HLS:ää käyttäen suunnittelu- ja varmennustyö voi keskittyä ominaisuuksiin ja korkean tason arkkitehtuuriin matalan tason yksityiskohtien sijaan. Tämän diplomityön tavoite oli määritellä ja implementoida korkean tason verifiointivuo (HLV-vuo) C++:lla kirjoitetulle HLS-suunnitelmalle. HLV-vuo hyödyntää ohjelmointikielien tarjoamaa suorituskykyä ja korkeampaa abstraktion tasoa kovonkuvauskielien sijaan ja siten minimoi RTL:n varmennukseen vaadittavaa työtä. HLV vuo implementoitiin tapaustutkimuksessa. HLS-suunnitelma varmennettiin C++ -verifiointiympäristössä, ja Catapult Coveragea käytettiin kattavuuden analysointiin. RTL-kattavuutta mitattiin universaalilla verifiointimetodologialla (UVM) tehdyssä ympäristössä. C++ varmennuksessa käytetyt testivektorit implementoitiin uudelleen UVM-ympäristössä, jotta RTL-kattavuuden lähtötaso olisi korkea ilman manuaalista RTL-analyysiä. C++-suunnitelma implementoitiin prediktorina (referenssimallina) UVM-testipenkkiin koodikattavuuden parantamiseksi. Tapaustutkimuksen tulokset osoittavat, että määritelty HLV-vuo on toteutettavissa käytännössä. Vuota käyttämällä saavutetaan merkittäviä suorituskyky- ja tuottavuusetuja C++ -testiympäristössä verrattuna UVM-ympäristöön. 90.60% koodikattavuuden saavuttavien C++ testivektoreiden uudelleenimplementoiti UVM-ympäristössä tuotti 96.90% RTL-kattavuuden. C++-predictorin implementointi oli merkittävä työkalu RTL-kattavuustavoitteen saavuttamisessa

From FPGA to ASIC: A RISC-V processor experience

This work document a correct design flow using these tools in the Lagarto RISC- V Processor and the RTL design considerations that must be taken into account, to move from a design for FPGA to design for ASIC

A generic debug interface for IP-integrated assertions

Der Entwurf von Hardware/Software Systemen ist auf eine solide Verifikationsmethodik angewiesen, die den ganzen Design Flow durchzieht. Viele Konzepte haben eine Erhöhung des Abstraktionsniveaus bei der Entwurfseingabe gemeinsam, wobei der modell-basierte Hardware-Entwurf einen vielversprechenden und sich verbreitenenden Ansatz darstellt. Assertion basierte Verifikation ermöglicht dem Entwickler die Spezifikation von Eigenschaften des Entwurfes und die Aufdeckung von Fällen, in denen diese verletzt werden. Während Assertions in Entwurfs- und Simulationsstadien weit verbreitet sind, ist der Ansatz, diese mit auf dem integrierten Schaltkreis (IC) zu fertigen, neuartig. In dieser Diplomarbeit soll ein von Infineon Technologies entwickeltes, auf UML basierendes Datenmodell, welches zur Erfassung von Entwurfsspezifikation und zur automatischen Code-Generierung genutzt wird dahingehend erweitert werden, die Beschreibung für im IC integrierte Assertions zu ermöglichen. Für diese Zwecke wird ein abstraktes Datenmodell beschrieben werden. Das Assertion Interface soll die spezifikationsgetreue Modellintegration gewährleisten, sowie IC interne Assertionresultate dem umgebenen System über das Interface zugänglich machen und damit zum Debugging während der Laufzeit ermöglichen. Ferner werden die Codegenerierungs Templates erläutert und einBeispielsystem eingeführt, um die beschriebenden Konzepte zu validieren.Nowadays electronic systems design requires fast time to market and solid verification throughout the entire design flow. Many concepts have been researched to raise the level of abstraction during the design entry phase, whereas model-based design is the most promising one. Assertion-based verification enables the developer to specify properties of the design and to get report if these are violated. Assertions are common during development and simulation of electronic products but often are not included in the final silicon. In this thesis an UML-based model defined at Infineon Technologies for capturing design specification information and to generate code automatically using templates, will be extended to allow the description of an abstract debuggable assertion interface for silicon assertions. With help of the assertion interface it shall be possible to verify the correct module integration and to monitor IP-internal assertion checker results. Besides, the code-generation templates for the assertion interface model will be described. To demonstrate the usability of the developed concepts an example system will be introduced to validate the approach.Ilmenau, Techn. Univ., Diplomarbeit, 200

High-level modelling languages

This paper gives an introduction to the latest developments in modern electronic design methodology. It will give a brief history of the evolution of design software in an attempt to explain the seemingly haphazard development up to the present-day situation

Design under test interface implementation and stimulus in the verification of a RISC-V vector accelerator

The production of a microprocessor is one of the most complex and expensive processes in the industry these days. These high costs are why big companies dedicate most of their efforts to design verification during the development of these projects. Design verification is vital to be able to deliver an error-free design. As the final manufacturing of these products is expensive, no company can afford to spend money on defective designs. Governments and associations are investing in research projects with the recent open-source trends. These allowed entities like the Barcelona Supercomputing Center (BSC) to start developing their designs. Considering how hard it is for these entities to receive inversions of this type, they have to work hard in design verification. One of the critical aspects of design verification involves applying the correct stimulus to the IPs or modules to be verified. The verification engineers must generate a correct but diverse stimulus to drive the design under test. These stimuli are often achieved using Universal Verification Methodology (UVM) and directed testbenches. However, this task is sometimes not easy, where the design under verification might have a very complex interface or have a vast range of stimulation possibilities. In this thesis, a UVM-based testbench is presented for the design verification of a RISC-V Vector Accelerator. From design specifications to the testbench implementation, this work explains its structure and the reasoning behind its specific characteristics. This testbench can provide random stimulus through the interface of the Accelerator and handle the execution of vector instructions from the RISC-V Vector specifications. Although it is full of features, we will be focusing on the module interface treatment part of the testbench in this work. Finally, we will review its strengths and weaknesses and how we could improve these