STM32F4 LAN8720 and LWIP porting and debugging records (3)

LAN8720 configuration: 
IP: 192.168.192.30 
Gateway: 192.168.192.1

A high frequency of ARP packets is detected

The content of the packet asks for the mac address of 192.168.192.1, and asks the responder to send to 192.168.192.30. 
It can be judged that LAN8720 may want to send packets across the network segment, but cannot find the network manager. 
So the gateway of LAN8720 is changed to 192.168.192.15, which is the IP of the PC. 
Then use wireshark to capture the packet. 
You can see the high-frequency error packet information. 
 
From the captured packet, you can see that the IP address and port are not what you want. 
Find the IP address assignment in the sendto function, the atomic routine, the assignment method is as follows:

upcb->remote_ip=*addr;1

The type of remote_ip in pcb is the same as the type of addr, both are: struct ip_addr *

/* This is the aligned version of ip_addr_t,
   used as local variable, on the stack, etc. */
struct ip_addr {
  u32_t addr;
};12345

So I changed my code to:

pcb->remote_ip.addr = 0x0FC0A8C0;1

So it was sent out.

When the content sent is an array, it will die in the sending function.

Call stack before sending: 

The call stack after calling sendto: 
 
Then it will crash when the stack is popped later.

If you try using an atomic routine, the code will also fall into a Hardfault. 
Atomic routine:

//UDP server sends data

void udp_demo_senddata(struct udp_pcb *upcb)

{

    struct pbuf *ptr;

    ptr=pbuf_alloc(PBUF_TRANSPORT,strlen((char*)tcp_demo_sendbuf),PBUF_POOL); //Apply for memory

    if(ptr)

    {

        ptr->payload=(void*)tcp_demo_sendbuf; 

        udp_send(upcb,ptr); //udp sends data

        pbuf_free(ptr); //release memory

    } 

} 

The strange thing is 

ptr->payload = (void*)tcp_demo_sendbuf; 

The payload does not use memcpy but is directly assigned by a pointer. 

According to the example on the Internet, change this to:

memset(ptr->payload, 0, ptr->len);

memcpy(ptr->payload, dataptr, sendsize); 

Then no error is reported. I don't know why the atomic one can run through.

The recvfrom function crashed

int len;

len = recvfrom(socket_n, _commandBuffer, len, MSG_DONTWAIT, (sockaddr *)&remoteaddr, &remoteaddrlen);

The problem is that the third parameter passed in, len, is the buffer length. 

The requested len is mistakenly passed in as a value. 

In the recvfrom function, memset is called to clear the buffer. Then the code crashes.