In #7497 port_background_task was renamed to port_background_tick
but the actual call site wasn't changed. This meant that it was
no longer called!
Rename more functions from task to tick to make it clearer which is
which.
There is a race between when we run background tasks and when we
sleep. If an interrupt happens between the two, then we may delay
executing the background task. On some ports we checked this for
TinyUSB already. On iMX RT, we didn't which caused USB issues.
This PR makes it more generic for all background tasks including
USB.
Fixes#5086 and maybe others.
A background callback must never outlive its related object. By
collecting the head of the linked list of background tasks, this will
not happen.
One hypothetical case where this could happen is if an MP3Decoder is
deleted while its callback to fill its buffer is scheduled.
In time, we should transition interrupt driven background tasks out of the
overall run_background_tasks into distinct background callbacks,
so that the number of checks that occur with each tick is reduced.
