Supervised Learning in Spiking Neural Networks with Phase-Change Memory Synapses

Spiking neural networks (SNN) are artificial computational models that have been inspired by the brain's ability to naturally encode and process information in the time domain. The added temporal dimension is believed to render them more computationally efficient than the conventional artificial neural networks, though their full computational capabilities are yet to be explored. Recently, computational memory architectures based on non-volatile memory crossbar arrays have shown great promise to implement parallel computations in artificial and spiking neural networks. In this work, we experimentally demonstrate for the first time, the feasibility to realize high-performance event-driven in-situ supervised learning systems using nanoscale and stochastic phase-change synapses. Our SNN is trained to recognize audio signals of alphabets encoded using spikes in the time domain and to generate spike trains at precise time instances to represent the pixel intensities of their corresponding images. Moreover, with a statistical model capturing the experimental behavior of the devices, we investigate architectural and systems-level solutions for improving the training and inference performance of our computational memory-based system. Combining the computational potential of supervised SNNs with the parallel compute power of computational memory, the work paves the way for next-generation of efficient brain-inspired systems

A Survey of Spiking Neural Network Accelerator on FPGA

Due to the ability to implement customized topology, FPGA is increasingly used to deploy SNNs in both embedded and high-performance applications. In this paper, we survey state-of-the-art SNN implementations and their applications on FPGA. We collect the recent widely-used spiking neuron models, network structures, and signal encoding formats, followed by the enumeration of related hardware design schemes for FPGA-based SNN implementations. Compared with the previous surveys, this manuscript enumerates the application instances that applied the above-mentioned technical schemes in recent research. Based on that, we discuss the actual acceleration potential of implementing SNN on FPGA. According to our above discussion, the upcoming trends are discussed in this paper and give a guideline for further advancement in related subjects

Design and test of a neural microprocessor

En aquest projecte, es dissenya un microprocessador neuronal per ser implementat en FPGAs. Aquesta tecnologia consisteix en un processador softcore basat en RISC-V descrit amb SystemVerilog que s'utilitza per controlar un coprocessador encarregat d'executar una xarxa neuronal spiking amb propagació directa descrita amb VHDL. El control es fa amb senyals que es generen a partir d'instruccions SIMD personalitzades definides en una extensió del conjunt d’instruccions RSIC-V. Per fer-ho, es modifica el processador de manera que pugui detectar i descodificar les noves instruccions emmagatzemades a la seva memòria de programa. Per facilitar la tasca de definir el contingut de la memòria del programa, s'utilitza un codi escrit en C i es desenvolupa un conjunt d'instruccions C personalitzades. Aquestes instruccions es basen en l'ús de macros i inline assembly, i la seva finalitat és facilitar i permetre l'ús de les instruccions personalitzades RISC-V en el codi d'alt nivell. Per demostrar el correcte funcionament del projecte, se simula el microprocessador neuronal i després es prova a l'FPGA d'una placa de desenvolupament Nexys 4, amb el coprocessador implementat per resoldre el problema XOR. La implementació del coprocessador es replica amb C i s'executa a l'FPGA utilitzant només el processador predeterminat sense modificar. Finalment, els resultats s'analitzen i es comparen per determinar les compensacions entre els dos enfocaments en termes de temps d'execució, consum d'energia i espai utilitzat.En este proyecto, se diseña un microprocesador neuronal para su implementación en FPGAs. Esta tecnología consiste en un procesador softcore basado en RISC-V descrito con SystemVerilog que se utiliza para controlar a un coprocesador encargado de ejecutar una red neuronal spiking con propagación directa descrita con VHDL. El control se realiza con señales que se generan a partir de instrucciones SIMD personalizadas definidas en una extensión del conjunto de instrucciones RSIC-V. Para ello, se modifica el procesador de forma que pueda detectar y descodificar las nuevas instrucciones almacenadas en su memoria de programa. Para facilitar la tarea de definir el contenido de la memoria del programa, se utiliza un código escrito en C y se desarrolla un conjunto de instrucciones C personalizadas. Estas instrucciones se basan en el uso de macros e inline assembly, y su finalidad es facilitar y permitir el uso de las instrucciones personalizadas RISC-V en el código de alto nivel. Para demostrar el correcto funcionamiento del proyecto, se simula el microprocesador neuronal y después se prueba en la FPGA de una placa de desarrollo Nexys 4, con el coprocesador implementado para resolver el problema XOR. La implementación del coprocesador se replica con C y se ejecuta en la FPGA utilizando sólo el procesador predeterminado sin modifcar. Por último, los resultados se analizan y se comparan para determinar las compensaciones entre ambos enfoques en términos de tiempo de ejecución, consumo de energía y espacio utilizado.In this project, a neural microprocessor is designed to be implemented in FPGAs. This technology consists of a RISC-V-based soft processor described in SystemVerilog that is used to control a coprocessor in charge of executing a feedforward spiking neural network described in VHDL. The control is done with signals that are generated from custom-designed SIMD instructions defined in a RISC-V ISA extension. To do it, the processor is modified such that it can detect and decode the new instructions stored in its program memory. To facilitate the task of defining the program memory contents, a code written in C is used and a set of custom C instructions is developed. These instructions are based on the use of macros and inline assembly, and their purpose is to facilitate and allow the use of the RISC-V custom instructions in the high-level code. To demonstrate the correct operation of the project, the neural microprocessor is simulated and then tested on the FPGA of a Nexys 4 development board, with the coprocessor implemented for solving the XOR problem. The coprocessor implementation is replicated with C and executed in the FPGA using only the default processor without being modified. Finally, the results are analyzed and compared to determine the trade-offs between the two approaches in terms of execution time, power consumption, and utilized space

Development of an interface for digital neuromorphic hardware based on an FPGA

Exploring and understanding the functioning of the human brain is one of the greatest challenges for current research. Neuromorphic engineering tries to address this challenge by abstracting biological mechanisms and translating them into technology. Via the abstraction process and experiments with the resulting technical system, an attempt is made to obtain information about the biological counterpart. One subsection of Neuromorphic Engineering (NE) are Spiking Neural Networks (SNN), which describe the structures of the human brain more and more closely than Artificial Neural Networks (ANN). Together with their dedicated hardware, SNNs provide a good platform for developing new algorithms for information processing. In the context of these neuromorphic hardware platforms, this paper aims to develop an interface for a digital hardware platform (SPINN-3 Development Board) to enable the use of industrial or conventional sensors and thus create new approaches for experimental research. The basis for this endeavor is a Field Programmable Gate Array (FPGA), which is placed as a gateway between the sensors and the neuromorphic hardware. Overall, the developed system provides a robust solution for a wide variety of investigations related to neuromorphic hardware and SNNs. Furthermore, the solution also offers suitable possibilities to monitor all processes within the system in order to obtain suitable measurements, which can be examined in search of meaningful results.Comment: Accepted for publication with Proceedings of the Unified Conference of DAMAS, InCoME and TEPEN Conferences (UNIfied 2023), Springer Natur

A spiking neural network for real-time Spanish vowel phonemes recognition

This paper explores neuromorphic approach capabilities applied to real-time speech processing. A spiking recognition neural network composed of three types of neurons is proposed. These neurons are based on an integrative and fire model and are capable of recognizing auditory frequency patterns, such as vowel phonemes; words are recognized as sequences of vowel phonemes. For demonstrating real-time operation, a complete spiking recognition neural network has been described in VHDL for detecting certain Spanish words, and it has been tested in a FPGA platform. This is a stand-alone and fully hardware system that allows to embed it in a mobile system. To stimulate the network, a spiking digital-filter-based cochlea has been implemented in VHDL. In the implementation, an Address Event Representation (AER) is used for transmitting information between neurons.Ministerio de Economía y Competitividad TEC2012-37868-C04-02/0