From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <4F96F786.8050700@domain.hid>
Date: Tue, 24 Apr 2012 20:57:10 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
MIME-Version: 1.0
References: <4F96F53C.2070204@domain.hid>
In-Reply-To: <4F96F53C.2070204@domain.hid>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Xenomai-help] rtcan I/O hang bug with
	/proc/rtcan/rtcan0/registers
List-Id: Help regarding installation and common use of Xenomai
	<xenomai.xenomai.org>
List-Unsubscribe: <https://mail.gna.org/options/xenomai-help>,
	<mailto:xenomai-help-request@domain.hid>
List-Archive: </public/xenomai-help>
List-Post: <mailto:xenomai@xenomai.org>
List-Help: <mailto:xenomai-help-request@domain.hid>
List-Subscribe: <https://mail.gna.org/listinfo/xenomai-help>,
	<mailto:xenomai-help-request@domain.hid>
To: Andrew Tannenbaum <trb@domain.hid>
Cc: xenomai@xenomai.org

On 04/24/2012 08:47 PM, Andrew Tannenbaum wrote:
> I'm running
> 
> 	Linux 2.6.38.8
> 	Xenomai 2.6.0
> 	Atom N270 CPU
> 
> I'm talking to CAN with a PEAK PCI SJA1000 CAN adapter.
> 
> I have a control loop running at 200 Hz, and I use it to drive a motor
> and read an encoder using rtcan.  My code is based on the
> rtcansend/rtcanrecv examples.
> 
> I found a bug where my control loop was hanging, and I've isolated the
> problem so that it may be reproduced with Xenomai supplied tools,
> without using my own code.
> 
> The problem is:
> 
> When I have a loop that is sending CAN packets, if I read
> /proc/rtcan/rtcan0/registers at the same time, it causes the loop to
> hang.  The hang is in rt_dev_sendto.
> 
> To reproduce:
> 
> Configure the CAN controller
> 
> 	$ rtcanconfig rtcan0 --baudrate=1000000 start
> 
> Send packets, in this case, SYNC messages at 1000 Hz
> with tty output 1 Hz.
> 
> 	$ rtcansend rtcan0 -i 0x80 -p 1000 -l 1000000
> 
> It will print CAN SYNC (0x80) messages:
> 
> 	<0x080> [0]
> 	<0x080> [0]
> 	...
> 
> In another window, read rtcan0/registers in a loop (10 Hz):
> 
> 	$ while :; do cat /proc/rtcan/rtcan0/registers; sleep .1; done

Hi Andrew,

I am probably not the one which will answer your question, because I
know nothing about CAN hardware. What I know however is that some
hardware registers, when read, have side effects. For instance reading
an interrupt status may deassert the hardware interrupt.

The code for /proc/rtcan/rtcan0/registers is compiled if
CONFIG_XENO_DRIVERS_CAN_DEBUG is #defined.

This would seem to indicate that perhaps some registers have side
effects, and so this /proc file more a debug tool than something which
should be used on a regular basis.

Regards.

-- 
                                                                Gilles.