@ -40,13 +40,14 @@ The library is composed of a \textit{transport}, the core class called \textit{c
The unit classes wrap the command and event \gls{API} described in \cref{sec:units-overview}; all classes and methods are annotated by documentation comments for easy understanding.
The unit classes wrap the command and event \gls{API} described in \cref{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 \cref{fig:pydemo}.
An example Python program displaying a test pattern on a \gls{LED} matrix using the \gls{I2C}-connected driver chip IS31FL3730 is presented in \cref{lst:py_api} as an illustration of the library usage. A photo of the produced \gls{LED} pattern can be seen in \cref{fig:pydemo}.
\todo[inline]{add left line next to this listing}
\begin{listing}[h]
\begin{minted}{python}
\begin{pythoncode}
#!/bin/env python3
#!/bin/env python3
import gex
# The I2C unit called 'i2c' is configured to use PB6 and PB7
\caption{\label{fig:pydemo}GEX Zero with the Micro Dot pHAT add-on board showing a test pattern}
\caption{\label{fig:pydemo}GEX Zero with the Micro Dot pHAT add-on board, showing a test pattern defined in a Python script}
\end{figure}
\end{figure}
\section{MATLAB integration}
\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}.
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 example in \cref{lst:matlab_api} demonstrates the use of MATLAB to calculate the frequency spectrum of an analog signal captured with GEX. The syntax needed to use the serial port transport (instead of a raw access to USB endpoints) is shown in a comment.
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.
\begin{listing}
\begin{matlabcode}
% The ADC unit called 'adc' is configured to use PA1 as Channel 0
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:
\caption{\label{lst:matlab_api} Calling the Python GEX library from a MATLAB script}
\end{listing}
\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 shown above, controlling a \gls{LED} matrix driver, is presented in \cref{lst:c_api_full}.
\begin{listing}
\begin{ccode}
#include <signal.h>
#include <assert.h>
#include "gex.h"
static GexClient *gex;
/** Signal handler closing the serial port at exit */
\caption{\label{lst:c_api_full} An example C program controlling GEX using the low-level GEX library; this code has the same effect as the Python script shown in \cref{lst:py_api}.}
\end{listing}
The reader might point out that this example is unnecessarily obtuse, and that the payloads could be constructed in a more readable way. Indeed, two better methods are available.
\caption{\label{lst:c_api_struct} The variable-length struct approach to payload building}
\end{listing}
The structure-based method utilizes C structs to access individual fields in the payload. Simple payloads can be represented by a struct without problems, but payloads of a dynamic length pose a challenge; we can either define a new struct for each required length, or, when the variable-length array is located at the end of the payload, a struct with the largest needed payload size is defined and the real length is then specified when sending the message. The latter approach is illustrated in \cref{lst:c_api_struct}.
\subsection{Using the Payload Builder Utility}
\begin{listing}
\begin{ccode}
uint8_t buff[20];
PayloadBuilder pb;
pb = pb_init(&buff, 20, NULL);
pb_u16(&pb, 0x61);
pb_u8(&pb, 0x00);
pb_u8(&pb, 0x18);
GEX_Send(bus, 2, buff, pb_length(&pb));
pb_rewind(&pb); // reset the builder for a new frame
\caption{\label{lst:c_api_pb}Building and sending payloads using the PayloadBuilder utility}
\end{listing}
The Payload Builder utility, which comes with the TinyFrame library, may be used to construct message payloads; its usage is shown in \cref{lst:c_api_pb}. The third parameter of \mono{pb\_init()} is optional: a pointer to a function called when the buffer overflows; this callback is used to flush the buffer and rewind it, or to throw an error.
Payload Builder is accompanied by Payload Parser, a tool doing exactly the opposite, parsing a binary payload. That is not needed in our example, but we will find Payload Parser useful when processing the response to a query command, or an asynchronous event payload. Where a variable is written to a payload with \mono{pb\_u8(\&pb, var)}, it is retrieved with \mono{pp\_u8(\&pp)}. The full API of those payload utilities can be found in their well-commented header files.
The \gls{I2C} unit provides access to one of the microcontroller's \gls{I2C} peripherals. More on the \IIC bus can be found in \cref{sec:theory-i2c}.
The \gls{I2C} unit provides access to one of the microcontroller's \gls{I2C} peripherals. More on the \IIC bus can be found in \cref{sec:theory-i2c}.
The unit can be configured to use either of the three standard speeds (Standard, Fast and Fast+) and supports both 10-bit and 7-bit addressing. 10-bit addresses can be used in commands by setting their highest bit (0x8000), as a flag to the unit; the 7 or 10 least significant bits will be used as the actual address.
The unit can be configured to use either of the three standard speeds (Standard, Fast and Fast+) and supports both 10-bit and 7-bit addressing. 10-bit addresses can be used in commands by setting their highest bit (0x8000), as a flag to the unit; the 7 or 10 least significant bits will be used as the actual address.
