return ERR_OK; }
low_level_input
它是实现网卡接收数据的函数。
它由ethernetif_input调用，具体参考ethernetif_input。
/** * Should allocate a pbuf and transfer the bytes of the incoming * packet from the interface into the pbuf. * * @param netif the lwip network interface structure for this ethernetif * @return a pbuf filled with the received packet (including MAC header) * NULL on memory error */ static struct pbuf * low_level_input(struct netif *netif) { struct ethernetif *ethernetif = netif->state; struct pbuf *p, *q; u16_t len; /* Obtain the size of the packet and put it into the \ variable. */ len = ; #if ETH_PAD_SIZE len += ETH_PAD_SIZE; /* allow room for Ethernet padding */ #endif /* We allocate a pbuf chain of pbufs from the pool. */ p = pbuf_alloc(PBUF_RAW, len, PBUF_POOL); if (p != NULL) { #if ETH_PAD_SIZE pbuf_header(p, -ETH_PAD_SIZE); /* drop the padding word */ #endif /* We iterate over the pbuf chain until we have read the entire * packet into the pbuf. */ for(q = p; q != NULL; q = q->next) { /* Read enough bytes to fill this pbuf in the chain. The * available data in the pbuf is given by the q->len * variable. * This does not necessarily have to be a memcpy, you can also preallocate * pbufs for a DMA-enabled MAC and after receiving truncate it to the * actually received size. In this case, ensure the tot_len member of the * pbuf is the sum of the chained pbuf len members. */ read data into(q->payload, q->len); } acknowledge that packet has been read(); #if ETH_PAD_SIZE pbuf_header(p, ETH_PAD_SIZE); /* reclaim the padding word */ #endif LINK_STATS_INC(link.recv); } else { drop packet(); LINK_STATS_INC(link.memerr); LINK_STATS_INC(link.drop); } return p; }
有关MEM
Opt.h中的配置宏
/* ------------------------------------ ---------- Memory options ---------- ------------------------------------ */ /** * MEM_LIBC_MALLOC==1: Use malloc/free/realloc provided by your C-library * instead of the lwip internal allocator. Can save code size if you * already use it. */ MEM_LIBC_MALLOC==1： 使用C库的malloc/free/realloc #ifndef MEM_LIBC_MALLOC #define MEM_LIBC_MALLOC 0 #endif /** * MEMP_MEM_MALLOC==1: Use mem_malloc/mem_free instead of the lwip pool allocator. * Especially useful with MEM_LIBC_MALLOC but handle with care regarding execution * speed and usage from interrupts! */ #ifndef MEMP_MEM_MALLOC #define MEMP_MEM_MALLOC 0 #endif /** * MEM_ALIGNMENT: should be set to the alignment of the CPU * 4 byte alignment -> #define MEM_ALIGNMENT 4 * 2 byte alignment -> #define MEM_ALIGNMENT 2 */ 设置内存对齐 #ifndef MEM_ALIGNMENT #define MEM_ALIGNMENT 1 #endif /** * 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 #endif /** * MEMP_SEPARATE_POOLS: if defined to 1, each pool is placed in its own array. * This can be used to individually change the location of each pool. * Default is one big array for all pools */ #ifndef MEMP_SEPARATE_POOLS #define MEMP_SEPARATE_POOLS 0 #endif /** * MEMP_OVERFLOW_CHECK: memp overflow protection reserves a configurable * amount of bytes before and after each memp element in every pool and fills * it with a prominent default value. * MEMP_OVERFLOW_CHECK == 0 no checking * MEMP_OVERFLOW_CHECK == 1 checks each element when it is freed * MEMP_OVERFLOW_CHECK >= 2 checks each element in every pool every time * memp_malloc() or memp_free() is called (useful but slow!) */ #ifndef MEMP_OVERFLOW_CHECK #define MEMP_OVERFLOW_CHECK 0 #endif /** * MEMP_SANITY_CHECK==1: run a sanity check after each memp_free() to make * sure that there are no cycles in the linked lists. */ #ifndef MEMP_SANITY_CHECK #define MEMP_SANITY_CHECK 0 #endif /** * MEM_USE_POOLS==1: Use an alternative to malloc() by allocating from a set * of memory pools of various sizes. When mem_malloc is called, an element of * the smallest pool that can provide the length needed is returned. * To use this, MEMP_USE_CUSTOM_POOLS also has to be enabled. */ #ifndef MEM_USE_POOLS #define MEM_USE_POOLS 0 #endif /** * MEM_USE_POOLS_TRY_BIGGER_POOL==1: if one malloc-pool is empty, try the next * bigger pool - WARNING: THIS MIGHT WASTE MEMORY but it can make a system more * reliable. */ #ifndef MEM_USE_POOLS_TRY_BIGGER_POOL #define MEM_USE_POOLS_TRY_BIGGER_POOL 0 #endif /** * MEMP_USE_CUSTOM_POOLS==1: whether to include a user file lwippools.h * that defines additional pools beyond the \ * by lwIP. If you set this to 1, you must have lwippools.h in your * inlude path somewhere. */ #ifndef MEMP_USE_CUSTOM_POOLS #define MEMP_USE_CUSTOM_POOLS 0 #endif /** * Set this to 1 if you want to free PBUF_RAM pbufs (or call mem_free()) from * interrupt context (or another context that doesn't allow waiting for a * semaphore). * If set to 1, mem_malloc will be protected by a semaphore and SYS_ARCH_PROTECT, * while mem_free will only use SYS_ARCH_PROTECT. mem_malloc SYS_ARCH_UNPROTECTs * with each loop so that mem_free can run. * * ATTENTION: As you can see from the above description, this leads to dis-/