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py: Add option to reduce GC stack integer size to save RAM. 

A new option MICROPY_GC_STACK_ENTRY_TYPE is added to select a custom type
instead of size_t for the gc_stack array items.  This can be beneficial for
small devices, especially those that are low on memory anyway.  If a device
has 1MB or less of heap (and 16-byte GC blocks) then this type can be
uint16_t, saving 128 bytes of RAM.
This commit is contained in:
Ayke van Laethem 2018-02-23 18:59:31 +01:00 committed by Damien George
parent 62b4bebf64
commit 31cf528c75
2 changed files with 10 additions and 1 deletions
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9
py/mpconfig.h
View File

@ -106,6 +106,15 @@
#define MICROPY_ALLOC_GC_STACK_SIZE (64)
#endif
// The C-type to use for entries in the GC stack. By default it allows the
// heap to be as large as the address space, but the bit-width of this type can
// be reduced to save memory when the heap is small enough. The type must be
// big enough to index all blocks in the heap, which is set by
// heap-size-in-bytes / MICROPY_BYTES_PER_GC_BLOCK.
#ifndef MICROPY_GC_STACK_ENTRY_TYPE
#define MICROPY_GC_STACK_ENTRY_TYPE size_t
#endif
// Be conservative and always clear to zero newly (re)allocated memory in the GC.
// This helps eliminate stray pointers that hold on to memory that's no longer
// used. It decreases performance due to unnecessary memory clearing.

2
py/mpstate.h
View File

@ -77,7 +77,7 @@ typedef struct _mp_state_mem_t {
byte *gc_pool_end;
int gc_stack_overflow;
size_t gc_stack[MICROPY_ALLOC_GC_STACK_SIZE];
MICROPY_GC_STACK_ENTRY_TYPE gc_stack[MICROPY_ALLOC_GC_STACK_SIZE];
uint16_t gc_lock_depth;
// This variable controls auto garbage collection. If set to 0 then the