Solaar reports on and controls Logitech devices (keyboards, mice, and trackballs) that connect to your computer via a Logitech USB receiver (a very small piece of hardware that plugs into one of your USB ports) and communicate with the receiver using Logitech’s HID++ protocol. It is designed to detect all devices paired with your receivers, and at the very least display some basic information about them.
At this moment, all Unifying receivers are supported (devices
with USB ID
046d:c532) as are several Lightspeed Receivers
and a dozen Nano receivers.
HID++ is a Logitech-proprietary protocol that extends the standard HID protocol for interfacing with keyboards, mice, and so on. It allows Logitech receivers to communicate with multiple devices and modify some features of the device on the device itself. As the HID++ protocol is proprietary, many aspects of it are unknown. Some information about HID++ has been obtained from Logitech but even that is subject to change and extension.
There are several versions of the HID++ and many Logitech receivers and devices that utilize it. Different receivers and devices implement different portions of HID++ so even if two devices appear to be the same in both physical appearance and behavior they may work completely differently underneath. (For example, there are versions of the M510 mouse that use different versions of the HID++ protocol.) Contrariwise, two different devices may appear different physically but actually look the same to software. (For example, some M185 mice look the same to software as some M310 mice.)
The software identity of a receiver can be determined by its USB id
(reported by Solaar and also viewable in Linux using
lsusb). The software
identity of a device can be determined by its Wireless PID as reported by
Even something as fundamental as pairing works differently for different
receivers. For Unifying receivers, pairing adds a new paired device, but
only if there is an open slot on the receiver. So these receivers need to
be able to unpair devices that they have been paired with or else they will
not have any open slots for pairing. Some other receivers, like the
Nano receiver with USB ID
046d:c534, can only pair with particular kinds of
devices and pairing a new device replaces whatever device of that kind was
previously paired to the receiver. These receivers cannot unpair. Further,
some receivers can pair an unlimited number of times but others can only
pair a limited number of times.
Only some connections between receivers and devices are possible. In should be possible to connect any device with a Unifying logo on it to any receiver with a Unifying logo on it. Receivers without the Unifying logo probably can connect only to the kind of devices they were bought with and devices without the Unifying logo can probably only connect to the kind of receiver that they were bought with.
Solaar uses the HID++ protocol to pair devices to receivers and unpair devices from receivers, and also uses the HID++ protocol to display features of receivers and devices. Currently it only displays some features, but can modify even fewer. For more information on HID++ features and their support see the features page.
Solaar does not do anything beyond using the HID++ protocol to change the behavior of receivers and devices. In particular, it cannot change how the operating system turns the keycodes that a keyboard produces into characters that are sent to programs. That is the province of HID device drivers and other software (such as X11).
Logitech receivers and devices have firmware in them. Some firmware
can be updated using Logitech software in Windows. For example, there are
security issues with some Logitech receivers and devices and Logitech has
firmware updates to alleviate these problems. Some Logitech firmware can
also be updated in Linux using
WARNING: Updating firmware can cause a piece of hardware to become
permanently non-functional if something goes wrong with the update or the
update installs the wrong firmware.
Solaar does keep track of some changeable state of a device between
invocations. When it starts, it restores on-line devices to their
previously-known state, and while running it restores devices to
their previously-known state when the device itself comes on line.
This information is stored in the file
Querying a device for its current state can require quite a few HID++ interactions. These interactions can temporarily slow down the device, so Solaar tries to internally cache information about devices. If the device state is changed by some other means, even sometimes by another invocation of the program, this cached information may become incorrect. Currently there is no way to force an update of the cached information besides restarting the program.
For many devices, Solaar shows the approximate battery level via icons that
show up in both the main window and the system tray. In previous versions
several heuristics to determine which icon names to use for this purpose,
but as more and more battery icon schemes have been developed this has
become impossible to do well. Solaar now uses the eleven standard
battery icon names
Solaar will use the symbolic versions of these icons if started with the
--battery-icons=symbolic. Because of external bugs,
these symbolic icons may be nearly invisible in dark themes.