The Orchestration Stack: The Impossible Task of Designing Software for Unknown Future Post-CMOS Hardware

Future systems based on post-CMOS technologies will be wildly heterogeneous, with properties largely unknown today. This paper presents our design of a new hardware/software stack to address the challenge of preparing software development for such systems. It combines well-understood technologies from different areas, e.g., network-on-chips, capability operating systems, flexible programming models and model checking. We describe our approach and provide details on key technologies

Analytical Exploration and Quantification of Nanowire-based Reconfigurable Digital Circuits

Integrated circuit development is an industry-driven high-risk high-stakes environment. The time from the concept of a new transistor technology to the market-ready product is measured in decades rather than months or years. This increases the risk for any company endeavouring on the journey of driving a new concept. Additionally to the return on investment being in the far future, it is only to be expected at all in high volume production, increasing the upfront investment. What makes the undertaking worthwhile are the exceptional gains that are to be expected, when the production reaches the market and enables better products. For these reasons, the adoption of new transistor technologies is usually based on small increments with foreseeable impact on the production process. Emerging semiconductor device development must be able to prove its value to its customers, the chip-producing industry, the earlier the better. With this thesis, I provide a new approach for early evaluation of emerging reconfigurable transistors in reconfigurable digital circuits. Reconfigurable transistors are a type of MOSFET that features a controllable conduction polarity, i.e., they can be configured by other input signals to work as PMOS or NMOS devices. Early device and circuit characterisation poses some challenges that are currently largely neglected by the development community. Firstly, to drive transistor development into the right direction, early feedback is necessary, which requires a method that can provide quantitative and qualitative results over a variety of circuit designs and must run mostly automatic. It should also require as little expert knowledge as possible to enable early experimentation on the device and new circuit designs together. Secondly, to actually run early, its device model should need as little data as possible to provide meaningful results. The proposed approach of this thesis tackles both challenges and employs model checking, a formal method, to provide a framework for the automated quantitative and qualitative analysis. It pairs a simple transistor device model with a charge transport model of the electrical network. In this thesis, I establish the notion of transistor-level reconfiguration and show the kinds of reconfigurable standard cell designs the device facilitates. Early investigation resulted in the discovery of certain modes of reconfiguration that the transistor features and their application to design reconfigurable standard cells. Experiments with device parameters and the design of improved combinational circuits that integrate new reconfigurable standard cells further highlight the need for a thorough investigation and quantification of the new devices and newly available standard cells. As their performance improvements are inconclusive when compared to established CMOS technology, a design space exploration of the possible reconfigurable standard cell variants and a context-aware quantitative analysis turns out to be required. I show that a charge transport model of the analogue transistor circuit provides the necessary abstraction, precision and compatibility with an automated analysis. Formalised in a DSL, it enables designers to freely characterise and combine parametrised transistor models, circuit descriptions that are device independent, and re-usable experiment setups that enable the analysis of large families of circuit variants. The language is paired with a design space exploration algorithm that explores all implementation variants of a Boolean function that employs various degrees and modes of reconfiguration. The precision of the device models and circuit performance calculations is validated against state-of-the-art FEM and SPICE simulations of production transistors. Lastly, I show that the exploration and analysis can be done efficiently using two important Boolean functions. The analysis ranges from worst-case measures, like delay, power dissipation and energy consumption to the detection and quantification of output hazards and the verification of the functionality of a circuit implementation. It ends in presenting average performance results that depend on the statistical characterisation of application scenarios. This makes the approach particularly interesting for measures like energy consumption, where average results are more interesting, and for asynchronous circuit designs which highly depend on average delay performance. I perform the quantitative analysis under various input and output load conditions in over 900 fully automated experiments. It shows that the complexity of the results warrants an extension to electronic design automation flows to fully exploit the capabilities of reconfigurable standard cells. The high degree of automation enables a researcher to use as little as a Boolean function of interest, a transistor model and a set of experiment conditions and queries to perform a wide range quantitative analyses and acquire early results.:1 Introduction 1.1 Emerging Reconfigurable Transistor Technology 1.2 Testing and Standard Cell Characterisation 1.3 Research Questions 1.4 Design Space Exploration and Quantitative Analysis 1.5 Contribution 2 Fundamental Reconfigurable Circuits 2.1 Reconfiguration Redefined 2.1.1 Common Understanding of Reconfiguration 2.1.2 Reconfiguration is Computation 2.2 Reconfigurable Transistor 2.2.1 Device geometry 2.2.2 Electrical properties 2.3 Fundamental Circuits 3 Combinational Circuits and Higher-Order Functions 3.1 Programmable Logic Cells 3.1.1 Critical Path Delay Estimation using Logical Effort Method 3.1.2 Multi-Functional Circuits 3.2 Improved Conditional Carry Adder 4 Constructive DSE for Standard Cells Using MC 4.1 Principle Operation of Model Checking 4.1.1 Model Types 4.1.2 Query Types 4.2 Overview and Workflow 4.2.1 Experiment setup 4.2.2 Quantitative Analysis and Results 4.3 Transistor Circuit Model 4.3.1 Direct Logic Network Model 4.3.2 Charge Transport Network Model 4.3.3 Transistor Model 4.3.4 Queries for Quantitative Analysis 4.4 Circuit Variant Generation 4.4.1 Function Expansion 5 Quantitative Analysis of Standard Cells 5.1 Analysis of 3-Input Minority Logic Gate 5.1.1 Circuit Variants 5.1.2 Worst-Case Analysis 5.2 Analysis of 3-Input Exclusive OR Gate 5.2.1 Worst-Case Analysis 5.2.2 Functional Verification 5.2.3 Probabilistic Analysis 6 Conclusion and Future Work 6.1 Future Work A Notational conventions B prism-gen Programming Interfaces Bibliography Terms & Abbreviation

A Physical Synthesis Flow for Early Technology Evaluation of Silicon Nanowire based Reconfigurable FETs

Silicon Nanowire (SiNW) based reconfigurable fieldeffect transistors (RFETs) provide an additional gate terminal called the program gate which gives the freedom of programming p-type or n-type functionality for the same device at runtime. This enables the circuit designers to pack more functionality per computational unit. This saves processing costs as only one device type is required, and no doping and associated lithography steps are needed for this technology. In this paper, we present a complete design flow including both logic and physical synthesis for circuits based on SiNW RFETs. We propose layouts of logic gates, Liberty and LEF (Library Exchange Format) files to enable further research in the domain of these novel, functionally enhanced transistors. We show that in the first of its kind comparison, for these fully symmetrical reconfigurable transistors, the area after placement and routing for SiNW based circuits is 17% more than that of CMOS for MCNC benchmarks. Further, we discuss areas of improvement for obtaining better area results from the SiNW based RFETs from a fabrication and technology point of view. The future use of self-aligned techniques to structure two independent gates within a smaller pitch holds the promise of substantial area reduction

Designing Efficient Circuits Based on Runtime-Reconfigurable Field-Effect Transistors

An early evaluation in terms of circuit design is essential in order to assess the feasibility and practicability aspects for emerging nanotechnologies. Reconfigurable nanotechnologies, such as silicon or germanium nanowire-based reconfigurable field-effect transistors, hold great promise as suitable primitives for enabling multiple functionalities per computational unit. However, contemporary CMOS circuit designs when applied directly with this emerging nanotechnology often result in suboptimal designs. For example, 31% and 71% larger area was obtained for our two exemplary designs. Hence, new approaches delivering tailored circuit designs are needed to truly tap the exciting feature set of these reconfigurable nanotechnologies. To this effect, we propose six functionally enhanced logic gates based on a reconfigurable nanowire technology and employ these logic gates in efficient circuit designs. We carry out a detailed comparative study for a reconfigurable multifunctional circuit, which shows better normalized circuit delay (20.14%), area (32.40%), and activity as the power metric (40%) while exhibiting similar functionality as compared with the CMOS reference design. We further propose a novel design for a 1-bit arithmetic logic unit-based on silicon nanowire reconfigurable FETs with the area, normalized circuit delay, and activity gains of 30%, 34%, and 36%, respectively, as compared with the contemporary CMOS version

Exploiting Transistor-Level Reconfiguration to Optimize Combinational Circuits on the Example of a Conditional Sum Adder

Silicon nanowire reconfigurable field effect transistors (SiNW RFETs) abolish the physical separation of n-type and p-type transistors by taking up both roles in a configurable way within a doping-free technology. However, the potential of transistor-level reconfigurability has not been demonstrated in larger circuits, so far. In this paper, we present first steps to a new compact and efficient design of combinational circuits by employing transistor-level reconfiguration. We contribute new basic gates realized with silicon nanowires, such as 2/3-XOR and MUX gates. Exemplifying our approach with 4-bit, 8-bit and 16-bit conditional carry adders, we were able to reduce the number of transistors to almost one half. With our current case study we show that SiNW technology can reduce the required chip area by 16 %, despite larger size of the individual transistor, and improve circuit speed by 26 %