This project introduces a new storage type -- settings. Settings are kept in your device's EEPROM. They are referred to as "persistent storage" because they retain their values even when the device is powered off. Settings are incredibly important, as they provide a way to store your application's operating parameters.
This project builds on the Timers application. It uses a single setting to store the reload value for a (one-shot) timer.
Settings are defined on the Settings page of the Features tab:
Every time you add a setting, a corresponding variable of the same name is created. This is very similar to (one-shot) timers, which also have corresponding variables.
Settings have the same list of types available to them as variables. You can directly use settings in math expressions, just as you would use regular variables. You will notice that in addition to all the properties variables have, settings of certain types can also be limited in the value range:
Since the settings are stored in the EEPROM, and EEPROMs have the maximum number of write cycles they can endure, avoid designs that constantly rewrite the setting data. Depleting an EEPROM IC is not as impossible as one might think!
Settings as Links to the Outside World
Since settings store your application's operating parameters, it is usually necessary to access them "from the outside." This project facilitates editing its setting through the device's web interface.
The web interface is enabled through the Web Dashboard page of the Features tab. Inside the Web Dashboard, there is a Settings sub-page. Every setting that needs to be exposed through the web interface must be manually added there. Since this application only has a single setting, it is this one setting that has been added to the Settings sub-page of the General group.
Once you add anything to the Web Dashboard, the Web (HTTP) Server is also automatically enabled.
Accessing the Web Interface
To access the web pages of your TPS, you will need to assign a valid IP address to it first. This is where the Ethernet page of the Features tab comes into play. The DHCP property is set to Enabled by default. Your TPS device will get a valid IP address from the DHCP server, but how will you know what this IP address is?
The simplest way is to use the Device Explorer:
Open it after the application is uploaded onto the device and starts running. Click Refresh to make sure you are looking at the latest data. The Device Explorer can be accessed at any time by pressing this button in the bottom left corner of the page:
Note the IP of your device, and point your browser to this IP. Voila, you have access to your application's lone setting:
Responding to Setting Value Changes
There is still one last trick to show you in this project: Responding to setting (variable) value changes. The On Variable Changed event block triggers every time the corresponding variable changes its value. In this application, changing the setting value will cause a debug message to be printed.
You can use the On Variable Changed block to report value changes for plain variables and settings but not for timers.