MacOS: Detect when audio devices are no longer valid

[pflarue]

Ideally, when a radio interface is disconnected from the computer, or for some USB direct connected radios like the QMX it is turned off, ardopcf should detect this and respond with RXENABLED FALSE, TXENABLED FALSE, and PTTENABLED FALSE host commands and RXAudio: DISABLED, RXAudio: DISABLED, and PTTControl: VOX/HOST at the top of the WebGUI screen.

When I tried this on a Mac with a QMX, it detected the loss of the serial connection for CAT PTT control, but did not seem to detect the loss of the audio devices. Upon turning the radio back on, the "Enable PTT/CAT Control" button in the WebGUI Config Controls worked as expected, but since it had not reacted to the loss of the audio devices, I had to click the Disable Audio Processing button and then click it again after it changed to an Enable Audio Processing button.

Can this be fixed?

[hessu]

On Linux, ALSA read/write returns an error when the device vanishes, triggering CloseSoundCapture/CloseSoundPlayback. On macOS, the AudioQueue callbacks keep running against a dead device silently, so nothing detects the loss.

I'll add an active check to notice the audio device going away.

[hessu]

#184 fixes this. The AudioQueue doesn't start yelling when the device goes away, it has to be actively polled for.

[pflarue]

PR #184 does not appear to fix this issue. A comment has been added to the PR.

While it would be nice if this can be fixed, it is not critical. To me, the primary benefit of ardopcf detecting disconnection or turning off of a radio or radio interface occurs when using a single board linux computer for portable operation. For that use case, accidental disconnection is more likely, and I believe that it is also more likely that the user will make these hardware changes while ardopcf is running. So, updating the status indicators on the WebGUI is useful to help the user understand the current program state. If these conditions are less likely to occur when using a MacOS device, then failure to detect the status changes may be less important.