stm32: Support static soft timer instances. #7143
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Signed-off-by: Damien George <damien@micropython.org>
This adds support for making static (ie not on the Python GC heap) soft timers. This can be useful for a board to define a custom background handler, or eventually for BLE/network processing to use instead of systick slots; it will be more efficient using soft timer for this. The main issue with using the existing code for static soft timers is that it would combine heap allocated and statically allocated soft_timer_entry_t instances in the same pairing-heap data structure. This would prevent the GC from tracing some of the heap allocated entries (because the GC won't follow pointers outside the heap). This commit makes it so that soft timer entries are explicitly marked, instead of relying on implicit marking by having the root of the pairing heap in the root pointer section. Also, on soft reset only the heap- allocated soft timers are deleted from the pairing heap, leaving the statically allocated ones. Signed-off-by: Damien George <damien@micropython.org>
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This adds support for making static (ie not on the Python GC heap) soft timers. This can be useful for a board to define some custom background handler, or eventually for BLE/network processing to use instead of systick slots; it will be more efficient using soft timer for this.
The main issue with using the existing code for static soft timers is that it would combine heap allocated and statically allocated
soft_timer_entry_tinstances in the same pairing heap data structure. This would prevent the GC from tracing some of the heap allocated entries (because the GC won't follow pointers outside the heap).This PR makes it so that soft timer entries are explicitly marked, instead of relying on implicit marking by having the root of the pairing heap in the root pointer section. This PR also deletes only the heap-allocated soft timers from the pairing heap on soft reset, leaving the statically allocated ones.
An alternative to this approach would be to have two separate pairing heaps, one for static and one for heap allocated entries, but for execution efficiency it's better to just have a single pairing heap.