ports/rp2: Configure heap for PSRAM.

PSRAM will be used exclusively if MICROPY_GC_SPLIT_HEAP == 0,
it will be added to RAM if MICROPY_GC_SPLIT_HEAP == 1,
and the system will fall back to RAM only if it's not detected.

Due to the size of PSRAM, GC stack was overflowing and causing
the GC to scan through the entire memory pool.

This caused noticable slowdowns during GC. Increase the stack
from 256 to 4096 bytes to avoid overflow and increase the
stack entry type size to accomodate 8MB+ PSRAM.

Changes:

ports/rp2/mpconfigport.h: Make split-heap optional and enable by default.
			  Increase GC stack entry type to uint32_t.
			  Raise GC stack size.

Co-authored-by: Kirk Benell <[email protected]>
Signed-off-by: Phil Howard <[email protected]>

Author: Gadgetoid

ports/rp2/mpconfigport.h

@@ -86,7 +86,15 @@
 #endif
 
 // Memory allocation policies
+#if MICROPY_HW_ENABLE_PSRAM
+#define MICROPY_GC_STACK_ENTRY_TYPE             uint32_t
+#define MICROPY_ALLOC_GC_STACK_SIZE             (1024) // Avoid slowdown when GC stack overflow causes a full sweep of PSRAM-backed heap
+#else
 #define MICROPY_GC_STACK_ENTRY_TYPE             uint16_t
+#endif
+#ifndef MICROPY_GC_SPLIT_HEAP
+#define MICROPY_GC_SPLIT_HEAP                   MICROPY_HW_ENABLE_PSRAM // whether PSRAM is added to or replaces the heap
+#endif
 #define MICROPY_ALLOC_PATH_MAX                  (128)
 #define MICROPY_QSTR_BYTES_IN_HASH              (1)