Data transfer using Lwip socket to server.

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Data transfer using Lwip socket to server.

Devanand Biradar
Hi All,

I am continuing my colleague work of data transfer using lwip socket to server.
To transfer the DATA to server in continuous certain interval.

Using LWIP 2.0.2 version with PPPos connection.

There i am facing some issues that after 2 lwip_write where data is  successfully getting transfer to server. But on 3rd try data is not getting transmitted to server.

So I have debug for this issue, And following is my observation:

1. In this case TCP_MSS is 1460 and TCP_SND_BUF is 2920.

2. First attempt, I am sending data buffer of 512 bytes through  lwip_write function. And on server side receiving 512 bytes.
After this operation  oversize_left 948 bytes. So 948 bytes memory is available to data copy and transfer

3. In 2nd attempt also, I am successfully sending  and receiving 512 bytes. then oversize_left 436 bytes.

4. In 3rd attempt, i am facing issue. where i want to send 512 byte,But available  memory  size is  436 bytes. Which is equal to oversize_left 436 bytes.
so tcp_pbuf_prealloc allocate new 1460 bytes  memory , Out of these 1460 bytes 76 bytes are used to transfer 512 data bytes(436+76 = 512). After this parameter is  pcb->unsent_oversize = 1384 bytes.
But I am not receiving data on server side .

 My observation is once first time allocated 1460 memory gets over after some data transfer, Newly allocated memory ( To copy data to transfer) is not getting transfer properly. And data not receiving at server side.

I have  tried with different data size also like (128, 256 bytes etc.). And observed same behavior.
Please suggest any changes required and any more debug points needed.


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