Calling tcp_output() sends the data, but that doesn't mean the buffer is
free afterwards: it stays allocated until the remote host acknowledges it.
At this point, lwip calls your 'sent' callback.
Simon
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Am 31. August 2016 12:22:08 nachm. schrieb anand arjunan
<anand.ar...@gmail.com>:
Hi,
I am using LWIP (Raw TCP mode) (in FreeRTOS) for handling http page
requests, construct the web page and send the page to the client. I have
set the TCP_SND_BUF as 8*TCP_MSS where TCP_MSS is 1460. There will be only
one client / browser connecting to the system at a time.
In the receive call back function, I constructed the entire web page and
used the tcp_write () (with TCP_WRITE_FLAG_COPY ) to send the data to LWIP
buffer. Due to memory limitations, I have to reuse a buffer size of 2.5 K
to construct the page before writing it to LWIP using tcp_write () as the
actual page size to be sent to client is more than 14 K. I was thinking
that as and when I call tcp_output () the data would be
sent instantaneously to the client. But, I got to know that tcp_Output()
does not work in the callback function and LWIP will start sending the
packets automatically once the control is out of the callback function.
Due to this limitation I slightly modified the design. I have made the
actual LWIP receive callback to just set another (second) callback function
so that the actual LWIP callback would return immediately (so that
tcp_output( ) can work). The second callback would actually construct the
page and would be invoked by http_poll function or some other timer.
Even this does not work. It still accumulates the data worth of of 8*1460
bytes fully and sends only that much to the client. Once the buffer is
full, tcp_sndbuf(pcb) returns zero and I cannot write anymore to it. I
thought this would return non zero value as I am calling tcp_output ( )
outside the LWIP calling function using a timer function.
I tried disabling the nagle's algorithm using tcp_nagle_disbale( ) before
transmitting the packets. That did not help either.
I want the data to be sent to the client (without accumulating) as and when
I call tcp_output( ) because of the limitation that I can construct only
2.5 K bytes of page at a time and reuse it to construct the next section of
the page.
Please help. Any help / pointers would be appreciated.
Thanks
LWIP_Starter
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