Andrey Skvortsov
8b6116fe6c
To be able to have quick position fix GNSS engine needs to know - predicted orbits data, - current time, - approximate position. Modem sends indications with requests, when it needs corresponding information. Predicted orbits can be injected using 'mmcli -m any --location-inject-assistance-data=<file>'. But to accelerate time to first fix after cold start extra information is needed like time and coarse position. Inject position requests are received, when GPS session is initiated using QMI_LOC_START. In inject position request modem sends information about its last known position. If last known position is zero, when this is a cold start and inject position is needed to improve TTFF. Last position from the modem is cached in ModemManager and is injected next time, when modem requests it. For example, if modem is restarted. When timestamp on injected position is too old, than position is ignored and location engine does cold start. Therefore current time is used for injected position. When injected position is far away the actual one (for example, after flight), after some time location engine falls back to cold start. Tested on Quectel EG25-G. Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
ModemManager
ModemManager provides a unified high level API for communicating with mobile broadband modems, regardless of the protocol used to communicate with the actual device (Generic AT, vendor-specific AT, QCDM, QMI, MBIM...).
Getting Started
ModemManager uses the meson build system. Meson is likely available as a package from your Linux distribution, but if not please refer to the Meson project for installation instructions. Once you have Meson installed you'll probably want to install libmbim and libqmi which most modems require.
After dependencies are installed you can build ModemManager with:
$ meson setup build --prefix=/usr --buildtype=release
$ ninja -C build
And after a successful build, install with:
$ sudo ninja -C build install
Using
ModemManager is a system daemon and is not meant to be used directly from the command line. However, since it provides a DBus API, it is possible to use 'dbus-send' commands or the new 'mmcli' command line interface to control it from the terminal. The devices are queried from udev and automatically updated based on hardware events, although a manual re-scan can also be requested to look for RS232 modems.
Implementation
ModemManager is a DBus system bus activated service (meaning it's started automatically when a request arrives). It is written in C, using glib and gio. Several GInterfaces specify different features that the modems support, including the generic MMIfaceModem3gpp and MMIfaceModemCdma which provide basic operations for 3GPP (GSM, UMTS, LTE) or CDMA (CDMA1x, EV-DO) modems. If a given feature is not available in the modem, the specific interface will not be exported in DBus.
Plugins
Plugins are loaded on startup, and must implement the MMPlugin interface. It consists of a couple of methods which tell the daemon whether the plugin supports a port and to create custom MMBroadbandModem implementations. It most likely makes sense to derive custom modem implementations from one of the generic classes and just add (or override) operations which are not standard. There are multiple fully working plugins in the plugins/ directory that can be used as an example for writing new plugins. Writing new plugins is highly encouraged! The plugin API is open for changes, so if you're writing a plugin and need to add or change some public method, feel free to suggest it!
License
The ModemManager and mmcli binaries are both GPLv2+ (See COPYING). The libmm-glib library and the ModemManager API headers are LGPLv2+ (See COPYING.LIB).
Code of Conduct
Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms, which you can find in the following link: https://www.freedesktop.org/wiki/CodeOfConduct
CoC issues may be raised to the project maintainers at the following address: modemmanager-devel-owner@lists.freedesktop.org