About LWIP (LAN8720) network data transmission problem

annysky2012

When doing system testing, I found that when LWIP (LAN8720) sends hexadecimal data, when there is 0x00 in the sent data, the network determines that a string of data has ended.
For example, the sent data is: aa 55 05 00 00 00 03 00 05 00 12 55 aa. Through debugging, the network only sends aa 55 05, and the following data is not sent.
This means that when encountering 0x00, the network considers it to be empty data.


Now the question is, what if I want to send data 0?
If a two-byte number is sent, for example, the number 3, the hexadecimal is 00 03, how to send it?


I hope to get an answer, urgent~~

Ansersion

Are you really using the native interface of LWIP (write/send)? The native interface must have the size of the data to be sent, such as write (int fd, const void * buf, size_t count); It seems that you are using an encapsulated interface, and there are string processing functions such as strlen in the interface that truncate the sent data.

加勒比海盗

The above situation will not occur when using the write function.

annysky2012

Ansersion Published on 2019-8-28 09:38 Are you really using the native interface of LWIP (write/send)? The native interface must have the size of the data to be sent, such as write (int fd, const v ...

The strlen function is indeed used, but I sent the number 0, not '\0'! ! ! Why is that?

annysky2012

Pirates of the Caribbean published on 2019-8-28 10:38 The above situation will not occur when using the write function.

I haven't tried it, I'll try it

annysky2012

Pirates of the Caribbean published on 2019-8-28 10:38 The above situation will not occur when using the write function.

I haven't tried this yet, I'll try it

Ansersion

annysky2012 posted on 2019-8-29 09:58 The strlen function is indeed used, but the number I sent is 0, not '\0'! ! ! Why is this?

'\0' == 0

That's not the number 0. The ASCII code for the number 0 is 48.

Another common mistake is to use strcpy as memcpy, which will also cause truncation.

annysky2012

Ansersion posted on 2019-8-29 11:43 annysky2012 posted on 2019-8-29 09:58 The strlen function is indeed used, but the number I sent is 0, not '\0&rsqu ...

That makes a lot of sense. When I sent data, I used strlen to determine the length of the data to be sent and to apply for memory. Logically, it should be applied by bytes. I confused strlen and sizeof. Now the problem has been solved, thank you!