This is mainly for RME RayDAT that has a fixed buffersize of 16k:
dev_name : hw:HDSPMxc2f6c5,0
channels : 36
min_rate : 32000
max_rate : 192000
min_bufz : 16384
max_bufz : 16384
min_nper : 4
max_nper : 512
However nperiod configuration determines the effective latency
regardless.
This is similar to https://github.com/jackaudio/jack1/blob/master/drivers/alsa/alsa_driver.c#L476-L486
This adds a basic support to use multiple sound-cards, currently
limited to two devices: In/Out with shared settings.
Advanced setups still have to resort to using the ARDOUR_ALSA_EXT
environment variable
This is intended to prevent crashes when unregister_port() modifies the contents of these
two members at the same time that something else is iterating over them.
This can help when running with very low latency and the
initial process callback is [indirectly] expensive.
E.g. load a heavy session the a RPi4, initial setup can pull
in a lot of data, which blocks the bus.
In particular with the ALSA backend this can lead to poll timeout
which effectively stops the backend.
When recover() successfully re-initializes the device,
processing can continue just like after an x-run.
This can happen during initial session load of "expensive"
sessions (in particular on slow systems, e.g. Raspberry Pi)
usually with synths. Worker thread pulls in many external
files in the background which blocks the bus for a long time.
resulting in a poll-timeout.
Theoretically this could be lock-free by using a queue of device
ports to be added/remove in sync in the process-callback, but
realistically adding/removing devices doesn't have to be rt-safe.
* PortEngine::available() implementation
* AudioEngine::connected() wrapper
Eventually we may re-introduce PortEngine::available along
with a libardour internal port-engine.
