Some ports need an extra operation to ensure that the main task is
awoken so that a queued background task will execute during an ongoing
light sleep.
This removes the need to enable supervisor ticks while I2SOut is operating.
Closes: #3952
This unifies the flash config to the settings used by the Boot ROM.
This makes the config unique per board which allows for changing
quad enable and status bit differences per flash device. It also
allows for timing differences due to the board layout.
This change also tweaks linker layout to leave more ram space for
the CircuitPython heap.
Before this, a background callback that was on the list when
background_callback_reset was called could have ended up in a state
that made it "un-queueable": its "prev" pointer could have been non-NULL.
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.
CALLBACK_CRITICAL_BEGIN is heavyweight, but we can be confident we do
not have work to do as long as callback_head is NULL.
This gives back performance on nRF.
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.
Jeff Epler
Scott Shawcroft