@ -26,7 +26,15 @@ Today's state of chip integration allows production costs of a complex system on
\subsection{Operating systems}
An \gls{os} is a computer program that supports a computer's basic functions, and provides services to other programs (or applications) that run on the computer. The applications provide the functionality that the user of the computer wants or needs. The services provided by the operating system make writing the applications faster, simpler, and more maintainable.
Over time, a lot of \textit{embedded}\glspl{os} suited for embedded systems were developed. An embedded \gls{os} is a type of \gls{os} that is embedded and specifically configured for a certain \gls{hw} configuration. \Gls{hw} that uses embedded \gls{os} is designed to be lightweight and compact, forsaking many other functions found in non-embedded (i.e. desktop) computer systems in exchange for efficiency at resource usage \cite{holt2014embedded}. This means that they are made to do specific tasks and do them efficiently.
Over time, a lot of \textit{embedded}\glspl{os} suited for embedded systems were developed. An embedded \gls{os} is a type of \gls{os} that is embedded and specifically configured for a certain \gls{hw} configuration. \Gls{hw} that uses embedded \gls{os} is designed to be lightweight and compact, forsaking many other functions found in non-embedded (i.e. desktop) computer systems in exchange for efficiency at resource usage \cite{holt2014embedded}. This means that they are made to do specific tasks and do them efficiently. Notable embedded \glspl{os} currently in use by consumers include:
\begin{itemize}
\item\textbf{Symbian} - used in cell phones, mainly ones made by Nokia
\item\textbf{Embedded Linux} - used in many other devices like printers, routers or smart TVs; Android \ref{f:android_scr} is a subset of embedded Linux
\item\textbf{BlackBerry \gls{os}} - for BlackBerry phones
\item\textbf{iOS} - subset of Mac \gls{os} X, used in Apple’s mobile devices Palm \gls{os}
\item\textbf{Windows Mobile}
\end{itemize}
\begin{figure}[ht!]
\centering
@ -34,40 +42,23 @@ Over time, a lot of \textit{embedded} \glspl{os} suited for embedded systems wer
\caption{The Android 5 (Lollipop) screenshot - the most common operating system is among embedded ones}\label{f:android_scr}
\end{figure}
%\begin{minipage}{\textwidth}
Notable embedded OSs currently in use by consumers include:
\begin{itemize}
\item\textbf{Symbian} - used in cell phones, mainly ones made by Nokia
\item\textbf{Embedded Linux} - used in many other devices like printers, routers or smart TVs; Android \ref{f:android_scr} is a subset of embedded Linux
\item\textbf{BlackBerry OS} - for BlackBerry phones
\item\textbf{iOS} - subset of Mac OS X, used in Apple’s mobile devices
Palm OS
\item\textbf{Windows Mobile}
\end{itemize}
%\end{minipage}
\subsection{Real-time operating systems}
A \gls{rtos} is just a special purpose \gls{os}. The \textit{real time} part of the name does not mean that the system responds quickly, it just means that there are rigid time requirements that must be met. If these time requirements are not met, the results can become inaccurate or unreliable\cite{jean2002microc}. Embedded systems frequently posses the real time requirement.
A \gls{rtos} is just a special purpose \gls{os}. The \emph{real time} part of the name does not mean that the system responds quickly, it just means that there are rigid time requirements that must be met. If these time requirements are not met, the results can become inaccurate or unreliable\cite{jean2002microc}. Embedded systems frequently posses the real time requirement. There are two kinds of \gls{rtos}:
%\begin{minipage}{\textwidth}
There are two kinds of \gls{rtos}:
\begin{description}
\item[Hard Real Time]- system delays are known or at least bounded. Said to be operating correctly if the system can return results within any time constraints.
\item[Soft Real Time]- critical tasks get priority over other tasks and will retain priority until the task is completed. This is another way of saying that real time tasks cannot be kept waiting indefinitely. Soft real time makes it easier to mix the system with other systems.
\end{description}
%\end{minipage}
\begin{description}
\item[Hard Real Time]- system delays are known or at least bounded. Said to be operating correctly if the system can return results within any time constraints.
\item[Soft Real Time]- critical tasks get priority over other tasks and will retain priority until the task is completed. This is another way of saying that real time tasks cannot be kept waiting indefinitely. Soft real time makes it easier to mix the system with other systems.
\end{description}
\subsection{Embedded Linux}
Linux itself is a kernel, but \textit{Linux} in day to day terms rarely means so. Embedded Linux generally refers to a complete Linux distribution targeted at embedded devices. There is no Linux kernel specifically targeted at embedded devices, the same Linux kernel source code can be built for a wide range of devices, workstations, embedded systems, and desktops though it allows the configuration of a variety of optional features in the kernel itself. In the embedded development context, there can be an embedded Linux system which uses the Linux kernel and other software or an embedded Linux distribution which is a prepackaged set of applications meant for embedded systems and is accompanied by development tools to build the system\cite{hallinan2010embedded}.
Linux itself is a kernel, but \emph{Linux} in day to day terms rarely means so. Embedded Linux generally refers to a complete Linux distribution targeted at embedded devices. There is no Linux kernel specifically targeted at embedded devices, the same Linux kernel source code can be built for a wide range of devices, workstations, embedded systems, and desktops though it allows the configuration of a variety of optional features in the kernel itself. In the embedded development context, there can be an embedded Linux system which uses the Linux kernel and other software or an embedded Linux distribution which is a prepackaged set of applications meant for embedded systems and is accompanied by development tools to build the system\cite{hallinan2010embedded}.
With the availability of consumer embedded devices, communities of users and developers were formed around theses devices: Replacement or enhancements of the Linux distribution shipped on the device has often been made possible thanks to availability of the source code and to the communities surrounding the devices. Due to the high number of devices, standardized build systems have appeared like OpenEmbedded, Buildroot, OpenWrt, and LTIB.
\subsection{Kernel}
The \textit{kernel} is the essential center of a computer \gls{os}, the core that provides basic services for all other parts of the \gls{os}\cite{bovet2005understanding}. It has complete control over what happens in the system. A kernel can be contrasted with a \textit{shell}, the outermost part of an \gls{os} that interacts with user commands. Kernel and shell are terms used more frequently in Unix or Unix-like operating systems than in IBM mainframe or Microsoft Windows systems.
The \emph{kernel} is the essential center of a computer \gls{os}, the core that provides basic services for all other parts of the \gls{os}\cite{bovet2005understanding}. It has complete control over what happens in the system. A kernel can be contrasted with a \emph{shell}, the outermost part of an \gls{os} that interacts with user commands. Kernel and shell are terms used more frequently in Unix or Unix-like operating systems than in IBM mainframe or Microsoft Windows systems.
\begin{figure}[ht!]
\centering
@ -126,7 +117,7 @@ The Atheros AR9331 is a highly integrated and cost effective \gls{ieee} 802.11n
\item External 16-bit \gls{ddram} or \gls{sdr} memory interface
\item\gls{spi} NOR Flash memory support
\item No external \gls{eeprom} needed
\item 4 \gls{lan} ports and 1 \gls{wan} port \gls{ieee}802.3 Fast Ethernet switch with auto-crossover, auto polarity
\item 4 \gls{lan} ports and 1 \gls{wan} port \gls{ieee}802.3 Fast Ethernet switch with auto-crossover, auto polarity
\item Fully integrated \gls{rf} front-end including \gls{pa} and \gls{lna}
Peter Babič
9 years ago