RE: [lwip-users] Throttling incoming TCP in receive callback usingraw API

[Bruce Sutherland]

Thank you Simon. This is a very helpful list! 

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> [mailto:lwip-users-bounces+bruce.sutherland=rfinnovations.com.
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> Sent: Thursday, 23 October 2008 12:41 PM
> To: Mailing list for lwIP users
> Subject: Re: [lwip-users] Throttling incoming TCP in receive 
> callback usingraw API
> 
> Bruce Sutherland wrote:
> > In our TCP receive callback, data is simply copied from the pbufs 
> > provided by lwip, into a serial ring buffer. As the serial port is 
> > much slower than the Ethernet port, we need a way to inform 
> lwip that 
> > we cannot receive more data when the serial buffer is full. 
> What is the mechanism to do this?
> > Should I delay calling tcp_recved in the case that the serial ring 
> > buffer is too full?
> That's exactly the way to do it. tcp_recved sends a window 
> update to the remote side while the ACK is sent by 
> stack-internal functions right after receiving.
> > If so, when will my receive callback be called again? Is there some 
> > better way to achieve this?
> >   
> The receive callback will be called again when new data 
> arrives, which can happen although you did not call 
> tcp_recved if the RX window is not yet full. If the window is 
> full, the client may send again after receiving a window 
> update from you.
> 
> I'm guessing the ETH connection is much faster than the 
> serial connection? In that configuration, I think it will be 
> enough to call tcp_recved after having sent the data on the 
> serial line. That way, you only have to make sure that the 
> TCP RX window is bigger than (or equal
> to) the serial buffer.
> > Our current implementation appears below, which calls 
> tcp_recved for 
> > all data as it arrives, and just throws an assertion if the serial 
> > ring buffer is too full to fit the data.
> >
> >   
> That's not a good idea as this assertion can appear very 
> often if the TCP sender sends faster than the serial port can 
> handle it.
> 
> 
> Simon
> 
> 
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