gex-thesis/ch.pc_software.tex

\chapter{Client Software}

With the communication protocol clearly defined in chapters \ref{sec:tinyframe} and \ref{sec:units-overview}, respective \ref{sec:wireless} for the wireless gateway, the implementation of a client software is relatively straightforward. Two proof-of-concept client libraries have been developed, in languages C and Python.

\section{General Library Structure}

The structure of a GEX support library is in all cases similar:

\begin{itemize}
	\item \textbf{USB or serial port access}
	
		This is the only platform-dependent part of the library. Unix-based systems provide a standardized POSIX API to configure the serial port. A raw access to \gls{USB} endpoints is possible using the libUSB C library. Access to the serial port or \gls{USB} from C on MS Windows has not been investigated, but should be possible using proprietary APIs. 
		
		Accessing the serial port or \gls{USB} endpoints from Python is more straightforward thanks to the cross platform libraries \textit{PySerial} and \textit{PyUSB}.
		
	\item \textbf{TinyFrame} 
	
		The \textit{TinyFrame} protocol library can be used directly in desktop C applications, and it has been ported to Python and other languages.
		 
	\item \textbf{Higher-level GEX logic} 
	
		The host side of the communication protocol described in chapter \ref{sec:tinyframe} should be implemented as a part of the library. This includes the reading and writing of configuration files, unit list read-out, command payload building, and asynchronous event parsing.
		
		Additional utilities may be defined on top of this basic protocol support for the command API of different GEX units, as described in \ref{sec:units-overview}. Those unit-specific ``drivers'' are available in the provided Python library.
\end{itemize}

\section{Python Library}

The Python GEX library it implements both serial port and raw USB endpoint access, and includes support classes for each unit type. Its development has been proritized over the C library because of it's potential to integrate with MATLAB, and the general ease-of-use that comes with the Python syntax.

The library is composed of a \textit{transport}, the core class called \textit{client}, and unit classes. Three transport implementations have been developed; the gateway is accessed by wrapping either of the transports in an instance of \mono{DongleAdapter}.

\begin{itemize}
	\item \mono{TrxSerialSync} -- virtual serial port access with polling for a response
	
	\item \mono{TrxSerialThread} -- virtual serial port access with a polling thread and semaphore-based notifications
	
	\item \mono{TrxRawUSB} -- similar to \mono{TrxSerialThread}, but using a raw USB endpoint access
\end{itemize}

The unit classes wrap the command and event \gls{API} described in chapter \ref{sec:units-overview}; all classes and methods are annotated by documentation comments for easy understanding.

An example Python program showing a pattern with the \gls{LED} matrix driver IS31FL3730 is presented below as an illustration of the library usage. A photo of the produced pattern can be seen in figure \ref{fig:pydemo}.

\begin{minted}{python}
#!/bin/env python3
import gex  
with gex.Client(gex.TrxRawUSB()) as client:
    bus = gex.I2C(client, 'i2c')
    addr = 0x61
    bus.write_reg(addr, 0x00, 0b00011000) # dual matrix
    bus.write_reg(addr, 0x0D, 0b00001110) # 34 mA
    bus.write_reg(addr, 0x19, 64) # set brightness
    # matrix 1
    bus.write_reg(addr, 0x01, [
        0xAA, 0x55, 0xAA, 0x55,
        0xAA, 0x55, 0xAA, 0x55
    ])
    # matrix 2
    bus.write_reg(addr, 0x0E, [
        0xFF, 0x00, 0xFF, 0x00,
        0xFF, 0x00, 0xFF, 0x00
    ])
    # update display
    bus.write_reg(addr, 0x0C, 0x01)
\end{minted}

\begin{figure}[h]
	\centering
	\includegraphics[width=.7\textwidth] {img/phatmtx.jpg}
	\caption{\label{fig:pydemo}GEX Zero with the Micro Dot pHAT add-on board showing a test pattern}
\end{figure}

\section{MATLAB integration}

The Python library can be accessed from MATLAB scripts thanks to the MATLAB's two-way Python integration \cite{matlabpy}. Controlling GEX from MATLAB may be useful when additional processing is required, e.g. with data from the \gls{ADC}; however, in many cases, an open source alternative native to Python exists that could be used for the same purpose, such as the NumPy and SciPy libraries \cite{numpyscipy}.

\todo[inline]{add a matlab example}

\section{C Library}

The C library is more simplistic than the Python one; it supports only the serial port transport (\gls{UART} or \gls{CDCACM}) and does not implement asynchronous polling or the unit support drivers. What \textit{is} implement---the transport, a basic protocol handler, and payload building and parsing utilities---is sufficient for most applications, though less convenient than the Python library. 

This low level library is intended for applications where the performance of the Python implementation is insufficient, or where an integration with existing C code is required. The full \gls{API} can be found in the library header files. A C version of the example Python script controlling a \gls{LED} matrix driver follows:

\todo[inline]{add the example}


\todo[inline]{Measurement / evaluation examples here...}