Re: [問題] KeilC 能否用malloc函數呢?使用SM5964 …
※ 引述《fmdjyl (小D(滴))》之銘言：
: 請問用keilc，使用單晶片sm5964(使用51架構)
: 請問能否使用malloc的函數呢(動態記憶體配置)
: 因為想省記憶體空間。
: 還請高手指教~
根據KEIL的說明：
malloc
Summary #include <stdlib.h>
void xdata *malloc (
unsigned int size); /* block size to allocate */
Description The malloc function allocates a memory block from the memory
pool of size bytes in length.
Note
Source code for this routine is provide in the LIB folder. You may modify the
source to customize this function for your particular hardware environment.
Return Value The malloc function returns a pointer to the allocated block
or a null pointer if there is not enough memory to satisfy the allocation
request.
See Also calloc, free, init_mempool, realloc
Example #include <stdlib.h>
#include <stdio.h> /* for printf */
void tst_malloc (void) {
unsigned char xdata *p;
p = malloc (1000); /* allocate 1000 bytes */
if (p == NULL)
printf ("Not enough memory space\n");
else
printf ("Memory allocated\n");
}
MALLOC.C
/*-----------------------------------------------------------------------------
MALLOC.C is part of the C51 Compiler package from Keil Software.
Copyright (c) 1995-2002 Keil Software. All rights reserved.
-----------------------------------------------------------------------------*/
#include <stdlib.h>
/*-----------------------------------------------
Memory pool block structure and typedefs.
Memory is laid out as follows:
{[NXT|LEN][BLK (LEN bytes)]}{[NXT|LEN][BLK]}...
Note that the size of a node is:
__mem__.len + sizeof (__mem__)
-----------------------------------------------*/
struct __mem__
{
struct __mem__ _MALLOC_MEM_ *next; /* single-linked list */
unsigned int len; /* length of following block */
};
typedef struct __mem__ __memt__;
typedef __memt__ _MALLOC_MEM_ *__memp__;
#define HLEN (sizeof(__memt__))
/*-----------------------------------------------
Memory pool headers. AVAIL points to the first
available block or is NULL if there are no free
blocks.
Note that the list is maintained in address
order. AVAIL points to the block with the
lowest address. That block points to the block
with the next higher address and so on.
-----------------------------------------------*/
extern __memt__ _MALLOC_MEM_ __mem_avail__ [];
#define AVAIL (__mem_avail__[0])
#define MIN_BLOCK (HLEN * 4)
/*-----------------------------------------------------------------------------
void _MALLOC_MEM_ *malloc (
unsigned int size); number of bytes to allocate
Return Value
------------
NULL FAILURE: No free blocks of size are available
NON-NULL SUCCESS: Address of block returned
-----------------------------------------------------------------------------*/
void _MALLOC_MEM_ *malloc (
unsigned int size)
{
__memp__ q; /* ptr to free block */
__memp__ p; /* q->next */
unsigned int k; /* space remaining in the allocated block */
/*-----------------------------------------------
Initialization: Q is the pointer to the next
available block.
-----------------------------------------------*/
q = &AVAIL;
/*-----------------------------------------------
End-Of-List: P points to the next block. If
that block DNE (P==NULL), we are at the end of
the list.
-----------------------------------------------*/
while (1)
{
if ((p = q->next) == NULL)
{
return (NULL); /* FAILURE */
}
/*-----------------------------------------------
Found Space: If block is large enough, reserve
if. Otherwise, copy P to Q and try the next
free block.
-----------------------------------------------*/
if (p->len >= size)
break;
q = p;
}
/*-----------------------------------------------
Reserve P: Use at least part of the P block to
satisfy the allocation request. At this time,
the following pointers are setup:
P points to the block from which we allocate
Q->next points to P
-----------------------------------------------*/
k = p->len - size; /* calc. remaining bytes in block */
if (k < MIN_BLOCK) /* rem. bytes too small for new block */
{
q->next = p->next;
return (&p[1]); /* SUCCESS */
}
/*-----------------------------------------------
Split P Block: If P is larger than we need, we
split P into two blocks: the leftover space and
the allocated space. That means, we need to
create a header in the allocated space.
-----------------------------------------------*/
k -= HLEN;
p->len = k;
q = (__memp__ ) (((char _MALLOC_MEM_ *) (&p [1])) + k);
q->len = size;
return (&q[1]); /* SUCCESS */
}
所以說，當然可以。但是必需用在XRAM上，而且原始版本只支援線性分配、
並且一樣會有一堆碎片、額外的配置表，如果你的CPU 有怪癖或奇怪構造（
記憶體折頁，分段.....） 你一樣得自己解決。
而除非你要寫網路驅動，或者USB BLOCK DEVICE。不然一般簡單的應用自己
管理一下分配分配其效率比較好啦～
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