Logitech Unifying Devices

Logitech have started shipping Unified devices, which means you can have up to 6 wireless devices connected to one little USB dongle thing. They’ve also invented a protocol called HID++, and it’s already in version 2. It’s basically a way to issue low level commands in a structured way to HID devices. It’s actually tons better than Bluetooth as it’s got a lower latency and also uses up less power on the sender and receiver.

I’m fairly familiar with low level protocols like this, as this is just the kind of thing the ColorHug is doing. Write a request packet, and get a response packet a few ms later. Julien Danjou had already added some support for the Unifying devices to UPower, albeit just for the K750 keyboard. Armed with a draft HID++v2 specification document and a newly purchased T620 I figured I could support most devices very easily by implementing the Battery Unified Level Status part of the specification.

Tuesday evening I started reading the specification sheet. By Wednesday lunchtime I had some test code in UPower that should have worked for all devices. But it didn’t. The percentage value was always 4%.

So, back to my trusty Windows XP VM. I loaded the Logitech client software, and that reported the percentage value correctly. I then dug out a hardware USB protocol analyser and made a trace of what the Windows client software was doing. Bingo. The BatteryLevelStatus ASE/SWID nibbles were swapped in the request packet. Either the documentation is wrong (unlikely, given the other ASE’s are the right way around) or the Logitech firmware engineer implementing the specification got them the wrong way around. I can’t blame them, the specification doesn’t explicitly specify an order, although you could easily work out what is likely as the byte order is specified as big endian.

I’ve pushed my patch to UPower. Testing very welcome.

15 responses to “Logitech Unifying Devices”

  1. Nathan Samson


    I have a K340 logitech keyboard & M505 mouse. Will I be able to use this new code to monitor the battery level from my laptop?

    Any idea when this change will be in fedora releases? I guess it will have to wait for Fedora 19?

    Is this/Will this be fully integrated in GNOME (and end up in the same indicator showing my laptop battery?)

    Thanks for the support,

  2. Bastien

    Glad to see the Beagle is of use :)

  3. James

    Sweet… I have one of these mice, which I like very much. The big missing feature was that I had to use a windows computer to get them all paired up to the same dongle.

    Besides the cool factor of being able to see my device battery life in gnome, do you have any ideas on how to use the data into a useful desktop feature? This could turn into a fun hack.

    Note that my mouse has on an onboard led battery indicator.


    1. James

      FWIW: Since I last paired my mouse things have changed. This now exists:


      and worked perfectly for me.

  4. Nathan Samson

    I have installed the SRPM on fedora 18, and rebooted.

    An additional “battery” (Accu) is added, but it is marked as Unknown and always at 0%.

  5. Jon Pritchard

    More awesomeness. Thank you.

  6. Beton

    One question – do you know if upower –monitor displays all devices that were detected using your patch? I have M325 mouse that is displayed, however my K360 keyboard is not.

    I could upload some logs if that would help finding a reason why it’s not detected.

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