Update the scheduling doc with some information about how async
scheduling works. Also add something about the latency.
Async links add 1 quantum of latency so take that into account when
aggregating latencies.
Also a source directly linked to an async node does not add latency
(we evaluate the tee before incrementing the cycle so that it effectively
is executed in the previous cycle and consumed immediately by async
nodes). We can do this because the driver source always provides data
before the async node, and never concurrently.
Add a listener to the link for the node driver change as well because
that can now influence the latency for async nodes.
The current situation is:
- The ALSA sequencer produces and consumes raw UMP only. Legacy input
is converted with the control mixer to UMP.
- All apps and plugins are made to consume and produce UMP.
- The control mixer can convert between UMP and MIDI when required.
- Legacy apps (pw-filter) will still receive MIDI1 events (converted by
the control mixer).
- Helper functions to convert UMP to and from MIDI can be used to ease
implementation when legacy MIDI is still required.
Using UMP natively over raw MIDI has some advantages:
- Transparent support for MIDI2 hardware and the new MIDI2 features
such as increased resolution for events, microtonal support, etc..
- Easy to convert between legacy MIDI and UMP
- Large SysEx can be fragmented properly.
- Fixed size messages are easier to parse and handle.
