%! TEX root = ../thesis.tex


\chapter{Introduction}

    This will be a short introduction to the BrainScaleS System and PowerIt.

\section{The BrainScaleS System}

    The BrainScaleS Wafer System which is visualized in \autoref{fig:wss}, developed and used in the electronic visions group at Heidelberg University is a neuromorphic hardware implementation~\cite{waferembedding}.
    On this Hardware, mixed-signal ASICs, or also called HICANNs, implement a behavior similar to that of a neuron found in biological systems.
    These ASIC chips are placed on a silicon wafer, and grouped into packs of 8, called reticles.
    With these Chips complex behavior of biological systems can be simulated.

    Focus of this thesis is part of the hardware implementation and only the following components will either be further examined or used later on:

    \begin{itemize}
        \item Control Units for Reticles, short CURe boards
        
            These boards control the power delivery mechanism for each of the 48 reticles. 
        \item Analog Breakout boards, AnaB for short
            
            Provided by these boards are direct connections to reticle voltages, two per reticle. These are normally shared between all 8 reticles. 
        \item and power supply, called PowerIt.
    \end{itemize}

    \begin{figure}[H]
        \centering
        \includegraphics[width=.7\textwidth]{pics/waferscale_system.png}
        \caption{The BrainScaleS wafer-scale hardware system, marked are the main components comprising a single wafer system.~\cite{hbpguidebook-brainscales}}\label{fig:wss}
    \end{figure}

\section{About the PowerIt Subsystem}

    The main subject of this thesis is the PowerIt board, photographed in \autoref{fig:pitteststand}. It functions as power supply inside of the WaferScale system, described before, in which it provides e.g. the wafer with \SI{1.8}{\volt} and the FPGAs with \SI{9.6}{\volt}. Its maximum rated power draw is \SI{2}{\kilo\watt}.~\cite{poweritupgrade}

    \begin{figure}[h]
        \centering
        \includegraphics[width=.7\textwidth]{./tikz/powerit.pdf}
        \caption{
            Photograph of the PowerIt boards top view.
            It receives \SI{48}{\volt} as input (magenta) and provides \SI{9.6}{\volt} (green) and \SI{1.8}{\volt} (analog: red, digital: blue)}\label{fig:pitteststand}
    \end{figure}

    This PowerIt board has a integrated STM32 microcontroller\footnote{STM32F405RGT~\cite{stm32f405xx}} which runs a custom firmware based on ChibiOS~\cite{chibios}.
    The PowerIt also measures the following values:

    \begin{itemize}
        \item input voltage and current
        \item \SI{1.8}{\volt} output voltage and current each for analog and digital parts of the wafer circuits
        \item and the \SI{9.6}{\volt} output voltage
    \end{itemize}

    which can then be used inside the firmware.

    The input voltage, nominal, is \SI{48}{\volt} and therefore the input current should not exceed \SI{41.7}{\ampere}
    Additionally the \SI{9.6}{\volt} are a set voltage obtained by the power supply modules\footnote{5:1 Bus converter IB0xxE096T48xx, 500W each}, which divide the input voltage by 5.
    Lastly the \SI{1.8}{\volt} output voltage is variable.


\newpage
\section{Contents in Detail}

    The first goal was to be able to change the calibration parameters.
    An upgrade for the PowerIt firmware was added to accomodate for those values.
    This was accomplished with a virtual memory map, which maps every parameter to a specific location and all of them can be changed.\\

    Calibrating the PowerIt was the next task.
    The calibration characterizes the voltage measuring circuits, whose voltages are either coming into or leaving the PowerIt.
    Additionally there are a current measuring circuits for incoming current and both \SI{1.8}{\volt} output currents.
    A reference voltage measurement was used to generate a fitted polynomial.
    This polynomials coefficients are the calibration parameters used inside the PowerIt.

    Taking these calibrations as basis, the \SI{1.8}{\volt} power supplies' behavior through different current draws could be observed.
    A simple model was generated from these measurements and applied.
    Also inside the formware a first iteration of that model was implemented and could now be tested.

    This all resulted in the testing and quntification of the regulation mechanism, as well as a secondary model that could be used in the future.