Appendix
Potential future extensions
- add the other parameters offered by the dtoverlay (e.g. absolute positioning, binary instead of Gray-code etc.)
- Add support for more than 3 encoders
- Add support for dtoverlays loaded at boot (similar to overlays for I2S DACs)
Known issues and limitations
Kernel warning when last overlay is removed
When the plugin is disabled, a kernel warning message about a potential memory leak is displayed when the last overlay is removed. I tried several things to prevent it and posted to several forums looking for help, but could not get rid of it. I consider it as not nice, but I could also not observe any issue after multiple disable/enable loops - so I decided to keep it as is for the time being. During normal use, the plugin will be configured once only and then loaded at boot and unloaded at shutdown - so you should never experience an issue. I use it for several months already without issues.
References
Device Tree Documentation
-
Kernel Documentation: rotary-encoder
Explains more about how a rotary works and how the DTOverlay is implemented -
Documentation of the
dtoverlaycommand
Search for 'rotary-encoder'. Alternatively, you can call
from the command line.dtoverlay -h rotary-encoder -
Documentation of the Raspberry Device Tree
If you would like to learn more about the details of the dtoverlay function.
NPM modules used
-
onoff
Since it was easier to implement and does not have any issues, I still use onoff for the push button. This could also be done with dtoverlay, but seems too much effort since it does not provide additional performance.