Network Write Delay using PPPD

Thu Jun 21 18:00:37 UTC 2001

Hello Mike,

> 
> Hi,
> I am using the i386/pc586 BSP with the latest snapshot.  My code
> is using the standard pppd task to establish a network connection.
> The ppp connection gets established and I can create a socket and 
> connect to my server test application.  
> 
> The RTEMS client code will write a block of data every time it 
> receives some data over the socket.  The problem that I am seeing 
> is that the client write seems to be getting delayed.  And the
> delay keeps getting longer after each successive write.  After four 
> writes, the delay is about 90 seconds!  I have turned off the pppd
> compression options.

1.) Maybe your "syslog" gets sent over the PPP connection. In the 
"standard" settings, PPP sends various messages to syslog during 
normal data transfer like (snapshot from my LINUX server syslog):

Jun 21 19:40:03 rtsys054 RTSYS-FW: Serial connection established.
Jun 21 19:40:04 rtsys054 RTSYS-FW: sent 18 bytes
Jun 21 19:40:31 rtsys054 last message repeated 9 times
Jun 21 19:40:34 rtsys054 RTSYS-FW: LCP: timeout sending Config-
Requests
Jun 21 19:40:34 rtsys054 RTSYS-FW: Connection terminated.
Jun 21 19:40:37 rtsys054 RTSYS-FW: Serial connection established.     

If this is the case, any packet sent (and received) will provoke a 
syslog entry which will provoke a PPP packet which will... You see 
where we might go to!

Most of the syslog outputs are controlled with the PPP variables 
"debug" and "kdebug", you should set them to zero, when you don't 
need logging.

Background info: In my configuration my RTEMS system has a Ethernet 
connection for normal use (and it is used for syslog transfers) and 
an additional UART for PPP, so in my configuration PPP's logging does 
not flood the PPP connection.

2) I have been using PPP together with a "hacked" version of rtems-
4.0.0 (I upgraded some parts like termios to the 4.5.0 version 
though). And it worked fine (more or less). Two weeks ago I ported my 
application to RTEMS-4.5.0 and I found that PPP receive gets a 
problem due to modifications in the RTEMS device driver interface: 
errno was not set at all, when a device driver error (like timeout 
during read) occured. Therefore I have changed 
"rtems/c/src/libfs/src/imfs/deviceio.c" (see attached file). Maybe 
this improves things too...

I would be very interested about your progress, because PPP in RTEMS 
seems to be still a bit difficult to work with.

Bye,
	Thomas.

--------------------------------------------
IMD Ingenieurbuero fuer Microcomputertechnik
Thomas Doerfler           Herbststrasse 8
D-82178 Puchheim          Germany
email:    Thomas.Doerfler at imd-systems.de
PGP public key available at: http://www.imd-systems.de/pgp_key.htm

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