pdn-soundmodem-linux 0.82.0

pdn-soundmodem-linux

Linux support for applications that run the pdn-soundmodem core in their own process over a USB radio interface: the Linux counterpart of pdn-soundmodem-windows. Published to NuGet as pdn-soundmodem-linux by the same release as the core, on the same version. The daemon does not use or reference this library; the core knows nothing about it.

Audio and PTT themselves need nothing new on Linux: the core's AlsaAudioInput, AlsaAudioOutput, Cm108Ptt, SerialPtt and AlsaMixer are what a station opens. What an application needs beyond them is knowing which card, hidraw node and serial port to open, whether it may, and what to do when it may not. That is this library.

What is here

• RadioInterfaces.Discover(): every ALSA sound card, with the CM108-compatible hidraw node and the serial port of the same USB device, grouped by the USB device they hang off in sysfs (the Linux counterpart of a Windows container ID). An AIOC comes back as one interface: its card (plughw:CARD=AllInOneCable,DEV=0), /dev/hidraw0 for PTT and /dev/serial/by-id/usb-AIOC_All-In-One-Cable_...-if04. Each has a Key (USB IDs and serial number, or USB port for a dongle with no serial number) for finding it again after card numbers have moved.
• DeviceAccess.Check: which of the nodes a station needs this process cannot open, and whether each is missing or refused, before anything is opened. The usual answer is the hidraw node, which is root's alone without a udev rule.
• CardUsers.Holder: who has a busy card open ("pipewire (pid 1234)"), from /proc/asound/.../status, so EBUSY can be explained.
• PipeWire.NodesFor: the card's PipeWire source and sink, and the pipewire:NODE=... ALSA device strings that go through PipeWire when the desktop will not let go of the card.
• MixerHygiene: the rules for a radio interface's mixer, as EndpointHygiene has them on Windows: nothing above 0 dB, AGC and mic boost off, neither side muted, and no input monitored to the output (a CM108's "Mic" playback switch, which sends received audio back to the transmitter). Controls are found by what they do as well as by name, because an AIOC calls its own "AIOC Audio In" and "AIOC Audio Out Volume".
• AlsaLevel: a card level in dB with a 0 dB ceiling, noticing changes made in alsamixer and putting back any that go above the ceiling.
• DeviceWatcher: an event when interfaces are plugged or unplugged (inotify on /dev).

Permissions

A packaged application should install a udev rule that gives the logged-in user (uaccess) and the audio group the interface's hidraw node, and its serial port, for example:

SUBSYSTEM=="hidraw", ATTRS{idVendor}=="0d8c", TAG+="uaccess", GROUP="audio", MODE="0660"
SUBSYSTEM=="hidraw", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="7388", TAG+="uaccess", GROUP="audio", MODE="0660"
SUBSYSTEM=="tty", ATTRS{idVendor}=="1209", ATTRS{idProduct}=="7388", TAG+="uaccess"

and a WirePlumber rule that keeps the desktop's sound server off radio interfaces, so that the card can be opened directly. pdn-lin, the Linux package of pdn-win, ships both.

Licence

AGPL-3.0-or-later, as the Windows library is and unlike the GPL-3.0-or-later core. It is new code written for the Linux application and derived from nothing in QtSoundModem or Dire Wolf; GPLv3 section 13 permits the combination.

Builds everywhere, runs on Linux

The project targets plain net10.0 and marks its Linux-only entry points with [SupportedOSPlatform("linux")]. Discovery, the access and holder diagnoses and the mixer rules all read through one seam (IDeviceTree, IAlsaMixer), so the tests (tests/Packet.SoundModem.Linux.Tests) run against written sysfs trees and fake cards on any platform; the real paths need a Linux machine with an interface attached.