Efficient Modelling and Simulation Methodology for the Design of Heterogeneous Mixed-Signal Systems on Chip

Systems on Chip (SoCs) and Systems in Package (SiPs) are key parts of a continuously broadening range of products, from chip cards and mobile phones to cars. Besides an increasing amount of digital hardware and software for data processing and storage, they integrate more and more analogue/RF circuits, sensors, and actuators to interact with their (analogue) environment. This trend towards more complex and heterogeneous systems with more intertwined functionalities is made possible by the continuous advances in the manufacturing technologies and pushed by market demand for new products and product variants. Therefore, the reuse and retargeting of existing component designs becomes more and more important. However, all these factors make the design process increasingly complex and multidisciplinary. Nowadays, the design of the individual components is usually well understood and optimised through the usage of a diversity of CAD/EDA tools, design languages, and data formats. These are based on applying specific modelling/abstraction concepts, description formalisms (also called Models of Computation (MoCs)) and analysis/simulation methods. The designer has to bridge the gaps between tools and methodologies using manual conversion of models and proprietary tool couplings/integrations, which is error-prone and time-consuming. A common design methodology and platform to manage, exchange, and collaboratively develop models of different formats and of different levels of abstraction is missing. The verification of the overall system is a big problem, as it requires the availability of compatible models for each component at the right level of abstraction to achieve satisfying results with respect to the system functionality and test coverage, but at the same time acceptable simulation performance in terms of accuracy and speed. Thus, the big challenge is the parallel integration of these very different part design processes. Therefore, the designers need a common design and simulation platform to create and refine an executable specification of the overall system (a virtual prototype) on a high level of abstraction, which supports different MoCs. This makes possible the exploration of different architecture options, estimation of the performance, validation of re-used parts, verification of the interfaces between heterogeneous components and interoperability with other systems as well as the assessment of the impacts of the future working environment and the manufacturing technologies used to realise the system. For embedded Analogue and Mixed-Signal (AMS) systems, the C++-based SystemC with its AMS extensions, to which recent standardisation the author contributed, is currently establishing itself as such a platform. This thesis describes the author's contribution to solve the modelling and simulation challenges mentioned above in three thematic phases. In the first phase, the prototype of a web-based platform to collect models from different domains and levels of abstraction together with their associated structural and semantical meta information has been developed and is called ModelLib. This work included the implementation of a hierarchical access control mechanism, which is able to protect the Intellectual Property (IP) constituted by the model at different levels of detail. The use cases developed for this tool show how it can support the AMS SoC design process by fostering the reuse and collaborative development of models for tasks like architecture exploration, system validation, and creation of more and more elaborated models of the system. The experiences from the ModelLib development delivered insight into which aspects need to be especially addressed throughout the development of models to make them reusable: mainly flexibility, documentation, and validation. This was the starting point for the development of an efficient modelling methodology for the top-down design and bottom-up verification of RF Systems based on the systematic usage of behavioural models in the second phase. One outcome is the developed library of well documented, parameterisable, and pin-accurate VHDL-AMS models of typical analogue/digital/RF components of a transceiver. The models offer the designer two sets of parameters: one based on the performance specifications and one based on the device parameters back-annotated from the transistor-level implementation. The abstraction level used for the description of the respective analogue/digital/RF component behaviour has been chosen to achieve a good trade-off between accuracy, fidelity, and simulation performance. The pin-accurate model interfaces facilitate the integration of transistor-level models for the validation of the behavioural models or the verification of a component implementation in the system context. These properties make the models suitable for different design tasks such as architecture exploration or overall system validation. This is demonstrated on a model of a binary Frequency-Shift Keying (FSK) transmitter parameterised to meet very different target specifications. This project showed also the limits in terms of abstraction and simulation performance of the "classical" AMS Hardware Description Languages (HDLs). Therefore, the third and last phase was dedicated to further raise the abstraction level for the description of complex and heterogeneous AMS SoCs and thus enable their efficient simulation using different synchronised MoCs. This work uses the C++-based simulation framework SystemC with its AMS extensions. New modelling capabilities going beyond the standardised SystemC AMS extensions have been introduced to describe energy conserving multi-domain systems in a formal and consistent way at a high level of abstraction. To this end, all constants, variables, and parameters of the system model, which represent a physical quantity, can now declare their dimension and associated system of units as an intrinsic part of their data type. Assignments to them need to contain besides the value also the correct measurement unit. This allows a much more precise but still compact definition of the models' interfaces and equations. Thus, the C++ compiler can check the correct assembly of the components and the coherency of the equations by means of dimensional analysis. The implementation is based on the Boost.Units library, which employs template metaprogramming techniques. A dedicated filter for the measurement units data types has been implemented to simplify the compiler messages and thus facilitate the localisation of unit errors. To ensure the reusability of models despite precisely defined interfaces, their interfaces and behaviours need to be parametrisable in a well-defined manner. The enabling implementation techniques for this have been demonstrated with the developed library of generic block diagram component models for the Timed Data Flow (TDF) MoC of the SystemC AMS extensions. These techniques are also the key to integrate a new MoC based on the bond graph formalism into the SystemC AMS extensions. Bond graphs facilitate the unified description of the energy conserving parts of heterogeneous systems with the help of a small set of modelling primitives parametrisable to the physical domain. The resulting models have a simulation performance comparable to an equivalent signal flow model

Proposal for a Bond Graph Based Model of Computation in SystemC-AMS

SystemC-AMS currently offers modelling formalisms with specialised solvers mainly focussing on the electrical domain. There is a need to improve its modelling capabilities concerning conservative continuous time systems involving the interaction of several physical domains and their interaction with nonconservative digital control components. Bond graphs unify the description of multi-domain systems by modelling the energy flow between the electrical and non-electrical components. They integrate well with block diagrams describing the signal processing part of a system. It is proposed to develop an extension to the current SystemC-AMS prototype, which shall implement the bond graph methodology as a new Model of Computation (MoC)

ModelLib: A Web-Based Platform for Collecting Behavioural Models and Supporting the Design of AMS Systems

This paper describes ModelLib, a web-based platform for collecting models from different domains (e.g. electrical, mechanical) and levels of abstractions. Use cases for this tool are presented, which show how it can support the design~process of complex AMS systems through better reuse of existing models for tasks like architecture exploration, system validation, and creation of more and more elaborated models of the system. The current state of the implemented ModelLib prototype is described and an outlook on its further development is given

Proposal to Extend SystemC-AMS with a Bond Graph Based Model of Computation

There is a need to improve the modelling capabilities of SystemC-AMS concerning conservative continuous time systems involving the interaction of several physical domains and the interaction with digital control components. Bond graphs unify the description of multi-domain systems by modelling the energy flow between the electrical and non-electrical components. They integrate well with block diagrams describing the signal processing part of a system. It is proposed to develop an extension to the current SystemC-AMS prototype, which shall implement the bond graph methodology as a new Model of Computation (MoC)

Ultrafast stamping by combination of synchronized galvanometer scanning with DOE’s or SLM

The up-scaling of laser micromachining processes with ultrashort pulses is limited due to heat accumulation and shielding effects. Multi beam scanning represents one of the strategies to overcome this drawback. It is in general realized by combining a diffractive beam splitter with a galvanometer scanner. A full synchronization with the laser repetition rate offers new possibilities with minimum thermal impact. We will demonstrate this by means of a multipulse-drilling on the fly process with a regular 5x5 spot pattern having a spot to spot spacing of 160µm. At a repetition rate of 100 kHz and an average power of 16 W we were able to drill more than 2’300 holes/s in a 10µm thick steel foil. We have further extended this technology with a special light modulator for different periodic spot patterns and more complex intensity distributions

Fostering the Reuse and Collaborative Development of Models in the AMS SoC Design Process

Systems-on-Chips (SoCs) integrate more and more heterogeneous components: analog/RF/digital circuits, sensors, actuators, software. For the design of these systems very different description formalisms, or Models of Computation (MoCs), and tools are used for the different subblocks and design stages, which often create interoperability problems. Additionally the verification of a complete SoC is difficult due to huge performance problems. The goal of this Ph.D. work is to develop an efficient modeling and simulation platform that supports the design of mixed-signal SoCs using component models written in different design languages and using different MoCs. One component of this work is the development of a web-based platform for collecting behavioral models and supporting the design of Analog and Mixed-Signal (AMS) SoCs. Its current state and an outlook on its further development is the focus of this paper