Re: "Spy'ing" characters sent thru serial port ?

[Willy Tarreau <willy@w.ods.org>]

Hello,

you might want to try to boot your software into an emulator such as vmware
and sniff the communications between the virtual machine and the real device.
This way, you will know if it is the OS which is retransmitting data to the
hardware.

Regards,
willy

On Wed, Jul 06, 2005 at 05:06:30PM +0200, Paul Rolland wrote:
> Hello,
> 
> We have a machine connected to a modem using the serial port, and from
> time to time, the modem complains the machine sent him a full 2K buffer
> (in fact, 2047 bytes) which were already sent.
> 
> We've been investigating at the application level, using strace to 
> monitor what is sent to the serial port, and at no time such a buffer is
> sent.
> 
> This problem is occuring on a random basis, and attempts to reproduce
> it in a test environment failed to date.
> 
> Is it possible to '(log|copy|...)' the chars that are sent on the
> serial port to some other place (without altering too much the performance
> of the machine, we are running the port a 9600bps), at the lowest level ?
> 
> Or is there a known issue of the serial port (or tty) buffer being 
> resent on the line in some weird conditions ? Any change done on 
> ->head and ->tail handling that could fix that ?
> 
> This problem is with Linux 2.4.27 (I know 2.4.31 is out, but nothing 
> related to that is present in the Changelog)
> 
> Regards,
> Paul
> 
> Paul Rolland, rol(at)as2917.net
> ex-AS2917 Network administrator and Peering Coordinator
> 
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