Re: [Xenomai] ARM, exception #0 ?

From: "George Pontis" <GPontis@z9.com>
To: xenomai@xenomai.org
Subject: Re: [Xenomai] ARM, exception #0 ?
Date: Wed, 27 Jun 2012 08:34:16 -0700	[thread overview]
Message-ID: <013901cd547a$50179b00$f046d100$@com> (raw)
In-Reply-To: <4FE9BDA9.3000209@xenomai.org>

> On 06/26/2012 03:23 PM, George Pontis wrote:
> > Running Xenomai 2.6.0 on an ARM at91sam9g45. I recently updated from
> Adeos
> > patch adeos-ipipe-3.0.13-arm-1.18-05 to adeos-ipipe-3.0.13-arm-1.18-
> 09. Then
> > built a new kernel and gave it to the application developers for a
> test.
> > There were other changes in the root FS and a few tweaks in the
> kernel, but
> > none that looked (to me) like they would affect Xenomai. They report
> this
> > new error:
> >
> >> Xenomai: Switching ADC Task to secondary mode after exception #0
> from
> >> user-space at 0xffff0fbc (pid 723)
> >
> > And then nothing about the app works any more. What does this mean ?
> 
> It means there is a fault, when the PC is around 0xffff0fbc, that is in
> the tsc emulation kernel helper. Could you try reverting this commit ?
> 

I tried reverting to adeos-ipipe-3.0.13-arm-1.18-05 without any other changes, and this error still occurs. The address of the exception is exactly the same. So I did some experiments to try to narrow this down. First thing, it does not happen with any Xenomai user app. I wrote a different app some time ago that runs without error on all the Xenomai-enabled kernels.

I also went back to a previous kernel where this app runs without causing the error. That kernel was the same 3.0.13 with adeos-ipipe-3.0.13-arm-1.18-05.patch and the same Xenomai 2.6.0. The root FS was identical. Everything was built with the same GCC 4.5.3. What was different about it were some other features that were enabled or disabled in the kernel. Possibly it is one or more of these changes that is aggravating the problem with this one app:

1) Turned off JFFS2, IDE
2) Turned on ext4 support
3) Enabled Atmel FB and SPI-based touchscreen controller
4) Disabled shmem
5) Disabled UID16 and "sysctl syscall"

Do any of these seem like they could be a factor ? I should emphasize that we are still pretty new to Xenomai. It is more likely that we have made a mistake in the app than that there is a Xenomai bug that nobody else has caught yet. Any suggestions where to go next to get to the bottom of this ?

George 