[Nut-upsdev] Developing the UPS side of the UPS-NUT equation (via usbhid)

Rob Groner rgroner at RTD.com
Thu Mar 6 20:55:42 UTC 2014

My company is developing a new UPS, with smarts provided by a PIC32 Microchip micro-controller.  The controller comes with a demo for a USBHID-UPS, and after some tweaking, I was able to get NUT to recognize it and start showing some reasonable values.

To make this UPS as easy to use as possible for the end-user who chooses Linux, I figured I would just completely implement the official USB HID UPS spec.  That way no subdriver would be needed, or at least very little.  However, I am having a terrible time making sense of the pages in the NUT guide for writing USB HID drivers, and the USB HID usage table at usb.org.  Just looking at some of the report ID values that I KNOW are working from the UPS example running on the microchip, I can't seem to find their equivalent in either doc.  For instance, I know that the UPS code is sending status info using a Report ID of 0x40 and two bytes of data...but I cannot find anything in the usb.org docs that relates to this.  NUT somehow understands it, though, since it correctly reports the device's status.

Can someone point me to a reference to make sense of the doc, or some hints to help me interpret what I'm seeing?



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