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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