浅析lwip_init==>mem_init()默认的内存初始化

lwip_init
==> mem_init();
/**
 * MEM_SIZE: the size of the heap memory. If the application will send
 * a lot of data that needs to be copied, this should be set high.
 */
#ifndef MEM_SIZE
#define MEM_SIZE                        1600 // opt.h中定义了heap大小[luther.gliethttp]
#endif

#define MIN_SIZE_ALIGNED     LWIP_MEM_ALIGN_SIZE(MIN_SIZE)
#define SIZEOF_STRUCT_MEM    LWIP_MEM_ALIGN_SIZE(sizeof(struct mem))
#define MEM_SIZE_ALIGNED     LWIP_MEM_ALIGN_SIZE(MEM_SIZE)

/** the heap. we need one struct mem at the end and some room for alignment */
static u8_t ram_heap[MEM_SIZE_ALIGNED + (2*SIZEOF_STRUCT_MEM) + MEM_ALIGNMENT]; // 之所乘以2,因为ram和ram_end将各占用一个[luther.gliethttp]
/** pointer to the heap (ram_heap): for alignment, ram is now a pointer instead of an array */
static u8_t *ram;
/** the last entry, always unused! */
static struct mem *ram_end;
/** pointer to the lowest free block, this is used for faster search */
static struct mem *lfree;
/**
 * Zero the heap and initialize start, end and lowest-free
 */
void
mem_init(void)
{
  struct mem *mem;

  LWIP_ASSERT("Sanity check alignment",
    (SIZEOF_STRUCT_MEM & (MEM_ALIGNMENT-1)) == 0);

  /* align the heap */
  ram = LWIP_MEM_ALIGN(ram_heap);   // 经过对齐之后ram指向ram_heap[]内存数组空间[luther.gliethttp]
  /* initialize the start of the heap */
  mem = (struct mem *)ram;
  mem->next = MEM_SIZE_ALIGNED;     // 表示mem从0到MEM_SIZE_ALIGNED大小都是归该ram管理,都是空闲的.
  mem->prev = 0;
  mem->used = 0;                    // 标识未使用
  /* initialize the end of the heap */
  ram_end = (struct mem *)&ram[MEM_SIZE_ALIGNED];
  ram_end->used = 1;
  ram_end->next = MEM_SIZE_ALIGNED;
  ram_end->prev = MEM_SIZE_ALIGNED;

  mem_sem = sys_sem_new(1);         // 创建内存互斥操作时所需的信号量[luther.gliethttp]

  /* initialize the lowest-free pointer to the start of the heap */
  lfree = (struct mem *)ram;        // ram包含的空间0-MEM_SIZE_ALIGNED全部可用.

  MEM_STATS_AVAIL(avail, MEM_SIZE_ALIGNED);
}