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Application Design Details

This document will cover the design details of the jxmot/tessel-networking-example project.

Table of contents generated with markdown-toc

Related Documents:

Application Initialize and Start Up

The t2 init command creates an index.js file with the following -

'use strict';

// Import the interface to Tessel hardware
const tessel = require('tessel');

// Turn one of the LEDs on to start.
tessel.led[2].on();

// Blink!
setInterval(() => {
  tessel.led[2].toggle();
  tessel.led[3].toggle();
}, 100);

A variation of that code is used in this application for the purpose of indicating that it is running. Additions to it have included -

  • Turning off the GPIO ports, which has the side effect of turning off the PORT A and PORT B LEDs.
  • Increasing the blink interval to 500ms.
  • Saving the timer id for a subsequent call to clearInterval().

In addition, index.js has been renamed to tessel-ap-test.js.

The remainder of the code in tessel-ap-test.js consistutes the remaining logic code for this application. Here is an overview of its operation :

Application overview flow chart

Access Point Initialization

This application initializes the access point programmatically. Here is an overview of how it's been accomplished :

Access Point Initialization flow chart

Wireless Network Interface Initialization

After the access point has been created and enabled, a periodic call to os.networkInterfaces() is made and its returned data is checked for the presence of an array labeled as "wlan0". When it is present and containing two elements it is evidence that the access point is running and available.

Wireless Network Interface Initialization flow chart

HTTP Server Initialization

The HTTP server has been implemented as a class. This makes it possible to instantiate more than one server. After a server has been initialized and is listening it can serve resources from one of two locations :

  • From the path to the docroot, where docroot was one of the arguments used when instantiating this class
  • From a common path. This path is shared by all instantiated servers. Its purpose is to server up 404 pages and other common file resources.

HTTP Server Initialization flow chart

User Path Handler

The userPaths argument to the httpsrv class is optional and can be used for providing a function to the server that handles application specific paths and/or endpoints. If it detects and responds to a request the function must return true. A return of false will indicate to httpsrv that the request was not handled and that it should satisfy the request.

HTTP Server Request Handling flow chart

Shutdown and Disable

When a signal(such as CTRL-C) is received by the application it will halt all interval timers and disable the access point. If this is not done the access point will continue to operate and accept connections even if the application is no longer running.

Shutdown and Disable flow chart

Tessel 2 Network API Modifications

The following functionality has been added to the Tessel 2 firmware -

  • Get/Set the WiFi channel
  • Request a list of stations currently connected to the access point

The required modifications are detailed in jxmot/tessel-networking-example/t2mods.md.

© 2018 J.Motyl