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RE: [lwip-users] netconn_write loops

From: Matthew Yingling
Subject: RE: [lwip-users] netconn_write loops
Date: Tue, 2 May 2006 10:08:40 -0400

In order for tcp_write() and tcp_output() to successfully complete, doesn't
the user code need to call LwIP to check for ACK packets to flush the data
out of the tcp_output queue?

Matthew Yingling

-----Original Message-----
From: address@hidden
[mailto:address@hidden Behalf Of
Christiaan Simons
Sent: Tuesday, May 02, 2006 4:02 AM
To: Mailing list for lwIP users
Subject: Re: [lwip-users] netconn_write loops

Edwin wrote:

> This problem has been posted in 2005 but got no response which i can
> in api_lib.c.
> In the function netconn_write the semaphore which is waited on when
> tcp_sndbuf( conn->pcb.tcp ) returns 0. There is mention of a patch of
> I expect that it will be integrated in lwip v 1.1.1.

If we're going to fix it, it will be changed in the HEAD version (CVS).

> But we still experience the connection loops in netconn_write at that
> In the api_msg.c in the function do_write, tcp_write is called.
> at some point tcp_write returns an error.

Do you remember which error? ERR_MEM is commonly returned by tcp_write(),
this indicates you'll have to back-off for a while so that tcp_output()
actually outputs the queued data.

> This isn't always a problem
> but sometimes it just keeps returning errors.

The correct usage of tcp_write(), tcp_output() etc
are described in the liwp/doc/rawapi.txt


Christiaan Simons

Hardware Designer
Axon Digital Design


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