102 lines
5.1 KiB
Markdown
102 lines
5.1 KiB
Markdown
---
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title: Solaar Capabilities
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layout: page
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---
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# Solaar capabilities
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[**Solaar**][solaar] reports on and controls [Logitech][logitech] devices
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(keyboards, mice, and trackballs) that connect to your computer via a
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Logitech USB receiver (a very small piece of hardware that plugs into one of
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your USB ports) and communicate with the receiver using Logitech's HID++
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protocol. Solaar is designed to detect all devices paired with your
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receivers, and at the very least display some basic information about them.
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At this moment, all [Unifying][unifying] receivers are supported (devices
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with USB ID `046d:c52b` or `046d:c532`) as are several Lightspeed Receivers
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and a dozen Nano receivers.
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## HID++
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HID++ is a Logitech-proprietary protocol that extends the standard HID
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protocol for interfacing with keyboards, mice, and so on. HID++ allows
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Logitech receivers to communicate with multiple devices and modify some
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features of the device on the device itself. As the HID++ protocol is
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proprietary many aspects of it are unknown. Some information about HID++
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has been obtained from Logitech but even that is subject to change and
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extension.
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There are several versions of the HID++ and many different Logitech
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receivers and devices that utilize it. Different receivers and devices
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implement different portions of HID++ so even if two devices appear to be
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the same in both physical appearance and behavior they may working
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completely differently underneath. (For example, there are versions of the
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M510 mouse that use different versions of the HID++ protocol.)
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Contrariwise, two different devices may appear different physically but
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actually look the same to software. (For example, some M185 mice look the
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same to software as some M310 mice.)
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The software identity of a receiver can be determined by its USB id
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(reported by Solaar and also viewable in Linux using `lsusb`). The software
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identity of a device can be determined by its Wireless PID as reported by
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Solaar.
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Even something as fundamental as pairing works differently for different
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receivers. For Unifying receivers, pairing adds a new paired device, but
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only if there is an open slot on the receiver. So these receivers need to
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be able to unpair devices that they have been paired with or else they will
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not have any open slots for pairing. Some other receivers, like the
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Nano receiver with USB ID `046d:c534`, can only pair with particular kinds of
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devices and pairing a new device replaces whatever device of that kind was
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previously paired to the receiver. These receivers cannot unpair. Further,
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some receivers can pair an unlimited number of times but others can only
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pair a limited number of times.
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Only some connections between receivers and devices are possible. In should
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be possible to connect any device with a Unifying logo on it to any receiver
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with a Unifying logo on it. Receivers without the Unifying logo probably
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can connect only to the kind of devices they were bought with and devices
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without the Unifying logo can probably only connect to the kind of receiver
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that they were bought with.
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## Supported features
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Solaar uses the HID++ protocol to pair devices to receivers and unpair
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devices from receivers. Solaar also uses the HID++ protocol to display
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features of receivers and devices. Solaar can modify some of the features
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of devices. Solaar currently only displays some features and can modify
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even fewer.
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Solaar does not do anything beyond using the HID++ protocol to change the
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behavior of receivers and devices. In particular, Solaar cannot change how
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the operating system turns the keycodes that a keyboard produces into
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characters that are sent to programs. That is the province of HID device
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drivers and other software (such as X11).
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Logitech receivers and devices have firmware in them. Some of the firmware
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can be updated using Logitech software in Windows. For example, there are
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security issues with some Logitech receivers and devices and Logitech has
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firmware updates to alleviate these problems. Some Logitech firmware can
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also be updated in Linux using `fwupdmgr`.
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WARNING: Updating firmware can cause a piece of hardware to to become
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permanently non-functional if something goes wrong with the update or the
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update installs the wrong firmware.
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Solaar does keep track of some of the changeable state of a device between
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invocations. When Solaar starts it restores on-line devices to their
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previously-known state. Also, while running Solaar restores devices to
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their previously-known state when the device comes on line.
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Querying a device for its current state can require quite a few HID++
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interactions. These interactions can temporarily slow down the device, so
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Solaar tries to internally cache information about devices. If the device
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state is changed by some other means, even sometimes by another invocation
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of Solaar, this cached information may become incorrect. Currently there is
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no way to force an update of the cached information besides terminating
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Solaar and starting it again.
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[solaar]: https://github.com/pwr-Solaar/Solaar
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[logitech]: https://www.logitech.com
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[unifying]: https://en.wikipedia.org/wiki/Logitech_Unifying_receiver
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