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Current capabilities is the set of *active* radios that can be used right now. Modem capabilities are the set of all radios the modem could use, if some action were performed to enable them if they are not enabled already (firmware reload, changing allowed mode, etc). For QMI devices, the DMS Get Capabilities command represents all radios, and thus "modem capabilities". But to read *current* capabilities, ie active radios, we need to query the NAS System Selection Preference and grab the "mode preference" TLV. Unfortunately that is only available with NAS >= 1.1, which means older Gobi devices (1K and 2K) don't support it. So for older devices, we try to get the Technology Preference (which takes into account user-requested limitations) and then mask that with the DMS Get Capabilities result for a best-effort current capabilities. For example, the Pantech UML290VW reports DMS Get Capabilities of "cdma, evdo, gsm, umts, lte", but a more limited SSP mode preference according to what modes are actually enabled. Gobi 1K devices don't support SSP, and the DMS Get Capabilities reports cdma/evdo or gsm/umts depending on the currently loaded firmware. Previous to this patch, ModemManager reported all modes as available on the UML290, ignoring what modes were actually enabled.
ModemManager. The problem ModemManager tries to solve is to provide a unified high level API for communicating with (mobile broadband) modems. While the basic commands are standardized, the more advanced operations (like signal quality monitoring while connected) varies a lot. Using. ModemManager is a system daemon and is not meant to be used directly from the command line. However, since it provides DBus API, it is possible to use 'dbus-send' command to control it from the terminal. There's an example program (tests/mm-test.py) that demonstrates the basic API usage. Implementation. ModemManager is a DBus system bus activated service (meaning it's started automatically when a request arrives). It is written in C. The devices are queried from udev and automatically updated based on hardware events. There's a GInterface (MMModem) that defines the modem interface and any device specific implementation must implement it. There are two generic MMModem implementations to support the basic operations (one for GSM, one for CDMA,) which are common for all cards. 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 MMModem 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's a fully working plugin in the plugins/ directory for Huawei cards that can be used as an example for writing new plugins. Writing new plugins is highly encouraged! API. The 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!