py/gc: Allow the GC heap to be split over multiple memory areas.

This commit adds a new option MICROPY_GC_SPLIT_HEAP (disabled by default)
which, when enabled, allows the GC heap to be split over multiple memory
areas/regions.  The first area is added with gc_init() and subsequent areas
can be added with gc_add().  New areas can be added at runtime.  Areas are
stored internally as a linked list, and calls to gc_alloc() can be
satisfied from any area.

This feature has the following use-cases (among others):
- The ESP32 has a fragmented OS heap, so to use all (or more) of it the
  GC heap must be split.
- Other MCUs may have disjoint RAM regions and are now able to use them
  all for the GC heap.
- The user could explicitly increase the size of the GC heap.
- Support a dynamic heap while running on an OS, adding more heap when
  necessary.

1 files changed, 6 insertions, 0 deletions

diff --git a/py/gc.h b/py/gc.h
index 5aef27c006..bb4204b06f 100644
--- a/py/gc.h
+++ b/py/gc.h
@@ -28,9 +28,15 @@
 
 #include <stdbool.h>
 #include <stddef.h>
+#include "py/mpconfig.h"
 
 void gc_init(void *start, void *end);
 
+#if MICROPY_GC_SPLIT_HEAP
+// Used to add additional memory areas to the heap.
+void gc_add(void *start, void *end);
+#endif
+
 // These lock/unlock functions can be nested.
 // They can be used to prevent the GC from allocating/freeing.
 void gc_lock(void);