Hi,
First of all if you have control over the host machine avoid sending 1 byte. This is not efficient.
I suggest adding a dual mechanism. Defining size and/or timeout.
I mean adding some mechanism that counts bytes ready to be sent. If you have more than X
Bytes you send them out. Also add a timeout. Meaning if you have collected less then X bytes
but a time period has elapsed since the last send, send it anyway. This way you force the sender
to send a minimum sized buffer and not send out 1 byte at a time with a large overhead...
At your device side you probably have a DMA collecting data. You may modify the code and check
How many bytes have you received. Similar to the above mechanism. If you got less than some limit
you do not allocate a pBuf ... only if you have a minimum data size or a time difference from last
data handling you allocate a pBuf, copy data to it and let the TCP stack handle it.
BR,
Noam.
-----Original Message-----
From: lwip-users [mailto:address@hidden On Behalf Of Oleg Gladyshev
Sent: Monday, November 07, 2016 3:23 PM
To:
address@hidden Subject: [lwip-users] Zero window and refused data problem
Hi all,
I develop a device which receives data from host machine using TCP (LwIP 1.4.1). Host sends data continuously queuing it to the controller.
Controller process data as fast as possible, but data process time is not determined. it can be from milliseconds to hours. And I wish to use TCP/IP incoming buffer as buffer for the data.
In my case TCP window on the device becomes full very often. Sometimes device's application receives from the TCP stack portion of data less than TCP windows size. This case LwIP doesn't update receive window leaving it zero. But the device able to receive some bytes now. And when the host sends 1 byte ZeroProbe packet device receives it.
For this one byte LwIP allocates new pbuf structure and sends it to application using sys_mbox_xxx call.
I use fixed-size mbox queues so after some probe packets from the host mbox becomes full and refuses new data. tcp_input notices this and tries to deliver refused data to the application every time it called.
But if application still refuses new data tcp_input() doesn't send ACK to the host! And host disconnects after some tries.
Making my mboxes dynamically doesn't solve the problem because in general we can waste all RAM with (TCP_WND-1) pbuf structures for every incoming byte from window probe packets.
I think it would be better to ACK with previous value to the host instead of silently dropping new data. What do you think about the issue? What is the best way to avoid disconnects in my project?
--
Best regards, Oleg
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