heap.c File Reference

VM Heap. More...

#include "pm.h"

Classes
struct	PmHeapDesc_s
struct	PmHeap_s
Defines
#define	__FILE_ID__   0x06
#define	HEAP_MAX_LIVE_CHUNK_SIZE   2044
#define	HEAP_MAX_FREE_CHUNK_SIZE   65532
#define	HEAP_MIN_CHUNK_SIZE   ((sizeof(PmHeapDesc_t) + 3) & ~3)
#define	OBJ_GET_GCVAL(pobj)   ((((pPmObj_t)pobj)->od >> OD_MARK_SHIFT) & 1)
#define	OBJ_SET_GCVAL(pobj, gcval)
Typedefs
typedef struct PmHeapDesc_s	PmHeapDesc_t
typedef struct PmHeapDesc_s *	pPmHeapDesc_t
typedef struct PmHeap_s	PmHeap_t
typedef struct PmHeap_s *	pPmHeap_t
Functions
PmReturn_t	heap_init (void)
PmReturn_t	heap_getChunk (uint16_t requestedsize, uint8_t **r_pchunk)
PmReturn_t	heap_freeChunk (pPmObj_t ptr)
uint16_t	heap_getAvail (void)

---

Detailed Description

VM Heap.

VM heap operations. All of PyMite's dynamic memory is obtained from this heap. The heap provides dynamic memory on demand.

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Define Documentation

#define HEAP_MAX_FREE_CHUNK_SIZE   65532

The maximum size a free chunk can be (a free chunk is one that is not in use). The free chunk size is limited by the size field in the *heap* descriptor. That field is fourteen bits with two assumed least significant bits (zeros): (0x3FFF << 2) == 65532

#define HEAP_MAX_LIVE_CHUNK_SIZE   2044

Checks for heap size definition. The maximum size a live chunk can be (a live chunk is one that is in use). The live chunk size is limited by the size field in the *object* descriptor. That field is nine bits with two assumed least significant bits (zeros): (0x1FF << 2) == 2044

#define HEAP_MIN_CHUNK_SIZE   ((sizeof(PmHeapDesc_t) + 3) & ~3)

The minimum size a chunk can be (rounded up to a multiple of 4)

#define OBJ_GET_GCVAL

(

pobj

)

((((pPmObj_t)pobj)->od >> OD_MARK_SHIFT) & 1)

Gets the GC's mark bit for the object. This MUST NOT be called on objects that are free.

#define OBJ_SET_GCVAL	(	pobj,
		gcval		)

Sets the GC's mark bit for the object This MUST NOT be called on objects that are free.

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Typedef Documentation

typedef struct PmHeapDesc_s PmHeapDesc_t

The following is a diagram of the heap descriptor at the head of the chunk:

MSb LSb 7 6 5 4 3 2 1 0 pchunk-> +-+-+-+-+-+-+-+-+ | S[9:2] | S := Size of the chunk (2 LSbs dropped) +-+-+-----------+ F := Chunk free bit (not in use) |F|R| S[15:10] | R := Bit reserved for future use +-+-+-----------+ | P(L) | P := hd_prev: Pointer to previous node | P(H) | N := hd_next: Pointer to next node | N(L) | | N(H) | Theoretical min size == 6 +---------------+ Effective min size == 8 | unused space | (12 on 32-bit MCUs) ... ... | end chunk | +---------------+

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Function Documentation

PmReturn_t heap_freeChunk

(

pPmObj_t

ptr

)

Places the chunk back in the heap.

Parameters:

ptr

Pointer to object to free.

uint16_t heap_getAvail

(

void

)

Returns:

Return number of bytes available in the heap

PmReturn_t heap_getChunk	(	uint16_t	requestedsize,
		uint8_t **	r_pchunk
	)

Returns a free chunk from the heap.

The chunk will be at least the requested size. The actual size can be found in the return chunk's od.od_size.

Parameters:

	requestedsize	Requested size of the chunk in bytes.
	r_pchunk	Addr of ptr to chunk (return).

Returns:

Return code

PmReturn_t heap_init

(

void

)

Initializes the heap for use.

Returns:

nothing.