Environment Variables for DFU

Certain reserved environment variables are available for scheduling and managing DFU actions.

Initiate DFU

After uploading a new host firmware binary to Notehub, or using an available Notecard firmware binary, you can initiate a host or Notecard DFU action by using the _fw or _fwc environment variables, respectively.

For example, to update your devices to a specific Notecard firmware version, copy the appropriate file name from Notecard Firmware Releases. Note that you will need to apply the appropriate firmware binary type to the correct Notecard devices (e.g. Notecard Cell+WiFi has a different firmware binary than Notecard WiFi), so it can be useful to have specific fleets set up that segment by device type.

Set the _fwc environment variable on the device, fleet, or project level:

Likewise, to initiate a host firmware binary update, set the _fw environment variable on the device, fleet, or project level:

Schedule DFU

If you need to ensure that DFU actions (whether they are host or Notecard updates) only occur during specific time periods, you may use the _dfu_period environment variable.

The value provided to this environment variable must be in the form of 0000000,00,0, which breaks down as follows:

1. 0000000 corresponds to days of the week, starting with Sunday.
   • For example, to enable DFU only on weekends, you would use 1000001.
2. 00 corresponds to the local time of the device in 24-hour clock format.
   • For example, to enable DFU starting at 5:00 PM, you would use 17.
3. 0 corresponds to how many hours the DFU window should remain open.
   • For example, to open the window for two hours, you would use 2.

Voltage-Variable DFU

Just as both hub.set and card.location.mode configurations can be customized to sync data or gather location information on a voltage-variable basis, DFU actions can be enabled/disabled in a similar way.

The _dfu_enabled environment variable allows you to enable DFU actions based on Notecard voltage thresholds already defined with the card.voltage API.

For example, to only enable DFU downloads when your device is powered by USB or the voltage is high or normal, you would use the following string:

usb:1;high:1;normal:1;low:0;dead:0