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+\documentclass[12pt]{article}
+\usepackage{euler}
+\usepackage[english]{babel}
+\usepackage{lipsum}
+\usepackage[colorlinks=true, urlcolor=blue, linkcolor=red]{hyperref}
+\newcounter{Chapcounter}
+\newcommand\showmycounter{\addtocounter{Chapcounter}{1}\themycounter}
+\newcommand{\chapter}[1] 
+{{\centering          
+  \addtocounter{Chapcounter}{1} \Large \underline{\textbf{ \color{blue} Chapter \theChapcounter: ~#1}} }   
+  \addcontentsline{toc}{section}{ \color{blue} Chapter:~\theChapcounter~~ #1}    
+}
+\hypersetup{colorlinks=true}
+\hypersetup{linkcolor=black}
+
+\title{Update PTU}
+\author{Gerhard Hoffmann}
+\date{\today}
+
+\begin{document}
+\maketitle
+\chapter{Introduction}
+    \section{Motivation}
+        The two main components of a PSA are
+        \begin{itemize}
+            \item PTU software.
+            \item Device controller (DC) firmware.
+        \end{itemize}
+    While the DC firmware is basically the same for each PSA (even for different
+    customers), the PTU software is highly dependent on customer requirements.\par
+    Hence, each customer is assigned an own git-repository, which will be loaded
+    ("cloned") on the PSA when configuring the machine for the first time.\par
+    Two special tools, the {\bf UpdateController} (a \href{https://doc.qt.io/qt-5/}{Qt}
+    binary [{\bf \nameref{UpdateTool}}]) and the {\bf UpdateScript}
+    (a \href{https://www.gnu.org/software/bash/manual/bash.html}{bash}
+    script [{\bf \nameref{UpdateScript}}]), work together to finish a PSA installation.\par 
+    
+    \section{PSA: Initial configuration}
+        For the initial configuration, a PSA loads a customer-specific git-repository,
+        which structure is detailed below [{\bf \nameref{repostructure}}].\par
+        The "git clone" for the repository is done by the UpdateScript [{\bf \nameref{UpdateScript}}].
+        It updates the file
+        \begin{center}
+            \fbox{
+                /opt/app/tools/atbupdate/update\_log.csv
+            }
+        \end{center}
+        which will be interpreted by the UpdateController [{\bf \nameref{UpdateTool}}].
+        The structure of {\bf update\_log.csv} is detailed below [{\bf \nameref{updatelogcsv}}].\par
+        Each line of {\bf update\_log.csv} represents a command for the UpdateController,
+        which will either download certain files to the DC or execute some
+        \href{https://openwrt.org/docs/guide-user/additional-software/opkg}{opkg}
+        commands [{\bf \nameref{opkg}}].
+        
+    \section{PSA: Update}
+    
+    \newpage
+    
+\chapter{Update-Tool "up\_dev\_ctrl"}
+    \section{up\_dev\_ctrl}
+    \label{UpdateTool}
+
+        The update-tool is a Qt binary ("up\_dev\_ctrl") and called by the
+        system-controller application. It is installed under
+        \begin{center}
+            \fbox{
+                /opt/app/tools/atbupdate/up\_dev\_ctrl
+            }
+        \end{center}
+
+        and has two responsibilities:
+        \begin{itemize}
+            \item Call update-script "update\_psa".
+            \item Update the device controller firmware.
+        \end{itemize}
+    \subsection{Calling the update-script "update\_psa"}
+        The update-script "update\_psa" is about executing all git-commands
+        necessary to clone and pull a customer repository.
+
+    \newpage
+
+\chapter{Update-Script "update\_psa"}
+    \section{update\_psa}
+    \label{UpdateScript}
+
+    Inside of such a
+        repository, there are at least the following directories:
+        \begin{itemize}
+           \item {\bf etc} 
+           \item {\bf etc/dc}\newline 
+                Contains the device controller firmware as binary file.
+           \item {\bf etc/psa\_config}\newline
+                Contains the printer template files (JSON).
+           \item {\bf etc/psa\_tariff}\newline
+                Contains the tariff files (JSON).
+           \item {\bf etc/psa\_update}\newline
+                Contains a single file for opkg-commands.
+        \end{itemize}
+    \newpage
+
+\chapter{Annex}
+    \section{Structure of a customer git-repository}
+    \label{repostructure}
+    
+    \section{Structure of "update\_log.csv"}
+    \label{updatelogcsv}
+    
+    \section{The package manager "opkg"}
+    \label{opkg}
+\end{document}