自写单片机malloc，高效利用ram，不再有内存碎片

最新推荐文章于 2025-10-24 10:42:18 发布

原创最新推荐文章于 2025-10-24 10:42:18 发布 · 置顶 · 1.3w 阅读

138 ·

CC 4.0 BY-SA版权

mcu 专栏收录该内容

20 篇文章

订阅专栏

本文介绍了一种针对单片机应用的内存管理方法，通过自定义内存分配算法避免内存碎片，提高内存利用率。该算法在分配内存时采用固定大小的堆空间，利用时间换空间的策略，在释放内存时重新组织堆空间，确保后续内存分配的连续性。

该文章已生成可运行项目，

单片机应用中，malloc/free产生内存碎片的原因：

标准内存动态分配是动态链表进行管理。由于malloc返回的是一个指针再加上单片机没有mmu，使得分配的指针就像一个个钉子钉在内存中了。这就导致内存管理非常困难，从而产生我们常说的内存碎片。

我们来举一个极端的例子，导致大量内存碎片：

1. 单片机的RAM为1Kbyte，为了说明和计算方便我们忽略掉链表占用的空间，只计算实际存储空间大小。

2. 申请64块内存空间，每块是16字节，那么就会分配完1k字节的空间。即：
for(int i=0; i<64; i++){
ptr[i] = malloc(16);
}

3. 然后释放掉偶数块内存空间，即：
for(int i=0; i<64; i+=2){
free(ptr[i] );
}

4. 于是我们释放掉了一半的RAM空间，即有512字节的空间，但是都是非连续的。32块16字节的非连续空间，所以要分配出大于16字节的内存块是分配不出来的。有512字节的空间但只能分配小于16字节的连续空间(除非使用calloc分配非连续空间)，在某些场合原本单片机RAM空间就很急，再加上这种不充分的使用使得程序稳定性大打折扣。

鉴于各中原因本人自己编写了一个内存管理，适合单片机使用的内存管理分配。

算法原理：
定义一个数组作为动态分配的堆空间，低地址空间保存管理数据，高地址空间实际分配给用户的缓存(类似堆栈使用，分配是往中间靠拢)，free时移动高地址用户空间(以时间换空间)，腾出多余未使用的空间，等待malloc来分配。

#include "mem_malloc.h"

static unsigned int sum = 0;
static char                     mem[MEM_SIZE];

#define DEBUG_EN        0
#define MEM_START       &mem[0]
#define MEM_END         &mem[MEM_SIZE]  
#define BLK_SIZE        sizeof(mem_block) 

void print_mem_info(void){
        printf("------------mem_info--------------\n");
        printf("sizeof(mem_block)=%d\n", BLK_SIZE);
        printf("MEM_START = %d(0x%x)\n", (int)MEM_START, (int)MEM_START);
        printf("MEM_END   = %d(0x%x)\n", (int)MEM_END, (int)MEM_END);
        printf("MEM_SIZE  = %d(0x%x)\n", (int)MEM_SIZE, (int)MEM_SIZE);
        printf("----------------------------------\n");
}

void print_hex(char *data, int len){
        for(int i=0; i<len; i++){
                printf("%02x ", (unsigned char)data[i]);
                if((i+1)%12 == 0)   printf("\n");
        }
        printf("\n");
}

void print_mem_hex(int size){
        print_hex(mem, size);
}

int mem_malloc(unsigned int msize){
        unsigned int all_size = msize + sizeof(mem_block);
        mem_block tmp_blk;
        if(msize == 0) return 0;
        if(sum){
                mem_block *ptr_blk = (mem_block *)(MEM_START + BLK_SIZE*(sum-1));
                int free_blk = (char *)ptr_blk->mem_ptr-(MEM_START + BLK_SIZE*sum);
                if(all_size <= free_blk){
                        tmp_blk.mem_ptr = ptr_blk->mem_ptr - msize;
                        tmp_blk.mem_size = msize;
                        tmp_blk.mem_index = ptr_blk->mem_index + 1;
                        memcpy(MEM_START + BLK_SIZE*sum, &tmp_blk, BLK_SIZE);
                        sum = sum + 1;
                #if DEBUG_EN
                        printf("mem_ptr = 0x%x\n", (int)tmp_blk.mem_ptr);
                        printf("mem_size = 0x%x\n", tmp_blk.mem_size);
                        printf("mem_index = 0x%x\n", tmp_blk.mem_index);
                #endif
                        return tmp_blk.mem_index;
                }
        }else{
                if(all_size <= MEM_SIZE){
                        tmp_blk.mem_ptr = MEM_END - msize;
                        tmp_blk.mem_size = msize;
                        tmp_blk.mem_index = 1;
                        memcpy(MEM_START, &tmp_blk, BLK_SIZE);
                        sum = 1;
        #if DEBUG_EN
                        printf("mem_ptr = 0x%x\n", (int)tmp_blk.mem_ptr);
                        printf("mem_size = 0x%x\n", tmp_blk.mem_size);
                        printf("mem_index = 0x%x\n", tmp_blk.mem_index);
        #endif
                        return 1;
                }
        }
        return 0;
}

void *mem_buffer(int id){
        for(int i=0; i<sum; i++){
                mem_block *ptr_blk = (mem_block *)(MEM_START + BLK_SIZE*i);
                if(id == ptr_blk->mem_index){
                        return ptr_blk->mem_ptr;
                }
        }
        return NULL;
}

void mem_free(int id){
        for(int i=0; i<sum; i++){
                mem_block *ptr_blk = (mem_block *)(MEM_START + BLK_SIZE*i);
                if(id == ptr_blk->mem_index){
                        mem_block *ptr_old;
                        if(i != (sum-1)){
                                int offset = ptr_blk->mem_size;
                                int move_size = 0; 
                                int n = sum - i;
                                mem_block *ptr_tmp;
                                for(int j=1; j<n; j++){
                                        ptr_tmp = (mem_block *)(MEM_START + BLK_SIZE*(i+j));
                                        move_size += ptr_tmp->mem_size;
                                }
                                //memmove();
                                char *dst_addr = ptr_tmp->mem_ptr + move_size + offset - 1;
                                char *src_addr = ptr_tmp->mem_ptr + move_size - 1;
                                for(int j=move_size; j>0; j--){
                                        *dst_addr-- = *src_addr--;
                                }
                                int len = dst_addr - src_addr + 1;
                                memset(src_addr, 0, len);
                                for(int j=0; j<(n-1); j++){
                                        ptr_tmp = (mem_block *)(MEM_START + BLK_SIZE*(i+j));
                                        ptr_old = (mem_block *)(MEM_START + BLK_SIZE*(i+j+1));
                                        memcpy(ptr_tmp, ptr_old, BLK_SIZE);
                                        ptr_tmp->mem_ptr += offset;
                                }
                        }else{
                                ptr_old = (mem_block *)(MEM_START + BLK_SIZE*i);
                                memset(ptr_old->mem_ptr, 0, ptr_old->mem_size);
                        }
                        memset(ptr_old, 0, BLK_SIZE);
                        sum = sum - 1;
                        break; 
                }
        }
}

main.c

#include "mem_malloc.h"

char mem_id[10]={0};

void test_malloc(int i, int size){
	printf("------test_malloc-------\n");
	mem_id[i] = mem_malloc(size);
	if(mem_id[i] == 0){
		printf("malloc --- fail\n");
		printf("size=%d\n", size);
	}else{
		char *p = mem_buffer(mem_id[i]);
        memset(p, i, size);
        printf("p = 0x%x, id=%d, size=%d\n", (int)p, mem_id[i], size);
	}
	print_mem_hex(MEM_SIZE);
}

void test_buffer(int i, int size){
	printf("------test_buffer-------\n");
	printf("id = %d, size=%d\n", mem_id[i], size);
	char *p = mem_buffer(mem_id[i]);
    if(p != NULL){
		memset(p, 0xf0+i, size);
        print_mem_hex(MEM_SIZE);
	}
}

void test_free(int id){
	printf("------test_free-------\n");
	printf("id = %d\n", mem_id[id]);
	mem_free(mem_id[id]);
	print_mem_hex( MEM_SIZE);
}

void main(void){

	print_mem_info();
	test_malloc(1, 10);
	test_malloc(2, 8);
	test_malloc(3, 20);
	test_free(2);
	test_malloc(4, 10);
	test_free(1);
	test_malloc(5, 20);
	test_malloc(6, 10);
	test_malloc(7, 10);
	test_free(6);
	test_malloc(8, 13);
	test_buffer(5, 20);
	test_free(4);
	test_buffer(3, 20);
	test_malloc(9, 15);
	test_malloc(10, 15);
}

结果：

------------mem_info--------------
sizeof(mem_block)=12
MEM_START = 134525056(0x804b080)
MEM_END = 134525184(0x804b100)
MEM_SIZE = 128(0x80) //方便演示以128字节空间测试
----------------------------------
------test_malloc-------
p = 0x804b0f6, id=1, size=10
f6 b0 04 08 0a 00 00 00 01 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 01 01
01 01 01 01 01 01 01 01 //第一次分配的10个字节空间
------test_malloc-------
p = 0x804b0ee, id=2, size=8
f6 b0 04 08 0a 00 00 00 01 00 00 00
ee b0 04 08 08 00 00 00 02 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 02 02 02 02 02 02 02 02 01 01 // 第二次分配的8个字节空间
01 01 01 01 01 01 01 01
------test_malloc-------
p = 0x804b0da, id=3, size=20
f6 b0 04 08 0a 00 00 00 01 00 00 00
ee b0 04 08 08 00 00 00 02 00 00 00
da b0 04 08 14 00 00 00 03 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 03 03 03 03 03 03
03 03 03 03 03 03 03 03 03 03 03 03 //第三次分配的20个字节空间
03 03 02 02 02 02 02 02 02 02 01 01
01 01 01 01 01 01 01 01
------test_free-------
id = 2
f6 b0 04 08 0a 00 00 00 01 00 00 00
e2 b0 04 08 14 00 00 00 03 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03 03 03 01 01 //释放掉了第二次分配的8字节空间
01 01 01 01 01 01 01 01
------test_malloc-------
p = 0x804b0d8, id=4, size=10
f6 b0 04 08 0a 00 00 00 01 00 00 00
e2 b0 04 08 14 00 00 00 03 00 00 00
d8 b0 04 08 0a 00 00 00 04 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 04 04 04 04 04 04 04 04 //第四次分配10字节空间
04 04 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03 03 03 01 01
01 01 01 01 01 01 01 01
------test_free-------
id = 1
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03 //释放掉了第一次分配的10字节空间
------test_malloc-------
p = 0x804b0ce, id=5, size=20
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
ce b0 04 08 14 00 00 00 05 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 05 05 05 05 05 05
05 05 05 05 05 05 05 05 05 05 05 05  //第五次分配20字节空间
05 05 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_malloc-------
p = 0x804b0c4, id=6, size=10
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
ce b0 04 08 14 00 00 00 05 00 00 00
c4 b0 04 08 0a 00 00 00 06 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 06 06 06 06 //第六次分配10字节空间
06 06 06 06 06 06 05 05 05 05 05 05
05 05 05 05 05 05 05 05 05 05 05 05
05 05 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_malloc-------
malloc --- fail
size=10
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
ce b0 04 08 14 00 00 00 05 00 00 00
c4 b0 04 08 0a 00 00 00 06 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 06 06 06 06 //剩余20字节-12字节=8字节，所以第七次分配10字节失败
06 06 06 06 06 06 05 05 05 05 05 05
05 05 05 05 05 05 05 05 05 05 05 05
05 05 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_free-------
id = 6
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
ce b0 04 08 14 00 00 00 05 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 05 05 05 05 05 05 //释放掉了第六次分配的10字节空间
05 05 05 05 05 05 05 05 05 05 05 05
05 05 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_malloc-------
p = 0x804b0c1, id=6, size=13
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
ce b0 04 08 14 00 00 00 05 00 00 00
c1 b0 04 08 0d 00 00 00 06 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 08 08 08 08 08 08 08 //第八次分配13字节空间
08 08 08 08 08 08 05 05 05 05 05 05
05 05 05 05 05 05 05 05 05 05 05 05
05 05 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_buffer-------
id = 5, size=20
ec b0 04 08 14 00 00 00 03 00 00 00
e2 b0 04 08 0a 00 00 00 04 00 00 00
ce b0 04 08 14 00 00 00 05 00 00 00
c1 b0 04 08 0d 00 00 00 06 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 08 08 08 08 08 08 08
08 08 08 08 08 08 f5 f5 f5 f5 f5 f5
f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 //修改第五次分配的空间内容
f5 f5 04 04 04 04 04 04 04 04 04 04
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_free-------
id = 4
ec b0 04 08 14 00 00 00 03 00 00 00
d8 b0 04 08 14 00 00 00 05 00 00 00
cb b0 04 08 0d 00 00 00 06 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 08 08 08 08 08 08 08 08 08
08 08 08 08 f5 f5 f5 f5 f5 f5 f5 f5
f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 //释放第四次分配的10字节空间
03 03 03 03 03 03 03 03 03 03 03 03
03 03 03 03 03 03 03 03
------test_buffer-------
id = 3, size=20
ec b0 04 08 14 00 00 00 03 00 00 00
d8 b0 04 08 14 00 00 00 05 00 00 00
cb b0 04 08 0d 00 00 00 06 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 08 08 08 08 08 08 08 08 08
08 08 08 08 f5 f5 f5 f5 f5 f5 f5 f5
f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3   //修改第三次分配的空间内容
f3 f3 f3 f3 f3 f3 f3 f3
------test_malloc-------
p = 0x804b0bc, id=7, size=15
ec b0 04 08 14 00 00 00 03 00 00 00
d8 b0 04 08 14 00 00 00 05 00 00 00
cb b0 04 08 0d 00 00 00 06 00 00 00
bc b0 04 08 0f 00 00 00 07 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
09 09 09 09 09 09 09 09 09 09 09 09  //第九次分配15字节空间
09 09 09 08 08 08 08 08 08 08 08 08
08 08 08 08 f5 f5 f5 f5 f5 f5 f5 f5
f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3
f3 f3 f3 f3 f3 f3 f3 f3
------test_malloc-------
malloc --- fail
size=15
ec b0 04 08 14 00 00 00 03 00 00 00
d8 b0 04 08 14 00 00 00 05 00 00 00
cb b0 04 08 0d 00 00 00 06 00 00 00
bc b0 04 08 0f 00 00 00 07 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00
09 09 09 09 09 09 09 09 09 09 09 09 //剩余12字节-12字节=0字节，所以第十次分配15字节失败
09 09 09 08 08 08 08 08 08 08 08 08
08 08 08 08 f5 f5 f5 f5 f5 f5 f5 f5
f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3 f3
f3 f3 f3 f3 f3 f3 f3 f3

源码：https://github.com/chenqy2018/mem_malloc

本文章已经生成可运行项目

12 条评论

Crkylin 2025.10.21
够硬核！

ps123654 2024.03.25
释放不对这代码有问题本人亲自测试

韬光养慧 2022.10.20
感谢分享，先学习

老虎爱3d 2022.10.05
假如有个任务挂起又恢复了，找不到原来的数据位置了怎么办

fsczp 2022.05.27
我在裸机里面用malloc然后跑飞了调到hardfault_handler，估计也是malloc和free使用不当导致的，要向大佬借鉴一下。

zevorn 2020.05.29
大佬，我用这个函数，编写链表，分配内存控件，可以吗单链表带头结点
- shareinfo2018回复zevorn 2020.08.03
  [reply]m0_46556792[/reply]可以的，最好在裸机中使用，而且不要中断函数中使用

qq_42564301 2019.01.07
数据结构设计的挺巧妙的，但是每次malloc和free都会改变之前已分配的内存的地址，会造成多个线程的使用的问题。比如对某个指针的引用。。。
- shareinfo2018回复qq_42564301 2019.01.09
  [reply]qq_42564301[/reply] 对，多线程使用比较麻烦，所以不建议

tianqi911 2018.10.09
高人你好，请问，您写的这个函数在哪种单片机上实际使用过了吗？比如51，stm32之类的。实际效果会有问题吗？
- tianqi911回复shareinfo2018 2018.10.12
  [reply]chenyefei[/reply] 谢谢高人的回答，那我也试试。之前用keil里的相同函数，想写个链表，总是错或者崩溃。
- shareinfo2018回复tianqi911 2018.10.12
  [reply]tianqi911[/reply] 移植到51单片机用过没问题，这个代码的缺陷是用在rtos代码应用非常繁琐。