Solaar/docs/capabilities.md

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Solaar Capabilities	page

Solaar capabilities

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). Solaar is designed to detect all connected devices, and at the very least display some basic information about them. At this moment, all Unifying receivers are supported (devices with USB ID 046d:c52b or 046d:c532) as are several Lightspeed Receivers and a dozen Nano receivers.

Solaar also reports on and controls some Logitech devices that directly connect to your computer using a USB cable or via Bluetooth. Not all such devices supported in Solaar as information needs to be added to Solaar for each device type that directly connects.

Most devices forget changed settings when the are turned off or go into a power-saving mode. Solaar keeps track of the settings that it has changed. The Solaar GUI application notices when devices reconnect and applies the remembered settings to the device.

HID++

The devices that Solaar handles use Logitech's HID++ protocol.

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 product ID (reported by Solaar and also viewable in Linux using lsusb). The software identity of a device that connects to a receiver can be determined by its Wireless PID as reported by Solaar. The software identity of devices that connect via a USB cable or via bluetooth can be determined by their USB or Bluetooth product ID.

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.

Supported features

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, and can modify even fewer. For a list of 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 fwupdmgr. 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 settings 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 ~/.config/solaar/config.json.

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.

Rule-based Processing of HID++ Feature Notifications

Solaar can process HID++ Feature Notifications from devices to, for example, change the speed of some thumb wheels. For more information on this capability of Solaar see the rules page. As much of rule processing depends on X11, this capability is only when running under X11.

Users can edit rules using a GUI by clicking on the Edit Rule button in the Solaar main window.

Solaar rules is an experimental feature. Significant changes might be made in response to problems.

Battery Icons

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 battery-{full,good,low,critical,empty}[-charging] and battery-missing.

Solaar will use the symbolic versions of these icons if started with the option --battery-icons=symbolic. Because of external bugs, these symbolic icons may be nearly invisible in dark themes.