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Date: Tue, 01 Apr 2014 00:11:24 +0200
From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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Subject: Re: [Xenomai] Porting xenomai 2.6.3 and ipipe to 3.12 kernel
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To: Lennart Sorensen <lsorense@csclub.uwaterloo.ca>
Cc: xenomai@xenomai.org

On 04/01/2014 12:04 AM, Lennart Sorensen wrote:
> On Mon, Mar 31, 2014 at 05:59:33PM -0400, Lennart Sorensen wrote:
>> On Mon, Mar 31, 2014 at 05:53:48PM -0400, Lennart Sorensen wrote:
>>> I am using the xenomai-2.6 git tree (current commit I see is as HEAD is
>>> 4081e1b032329bf0cc9442f466233d5fc1083fc5).
>>>
>>> Doing a git pull I see I am 4 commits behind, and one does sound
>>> interesting.  I will have to update that.
>>
>> Hmm, the interesting patch does the same thing I already did myself to
>> get it to compile.  I guess that is OK then.
> 
> Hmm, gdb is being not helpful at all:
> 
> root@omap5:/mnt/xenomai-2.6.3# gdb /usr/lib/xenomai/testsuite/latency 
> GNU gdb (GDB) 7.4.1-debian
> Copyright (C) 2012 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "arm-linux-gnueabihf".
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>...
> Reading symbols from /usr/lib/xenomai/testsuite/latency...done.
> (gdb) run
> Starting program: /usr/lib/xenomai/testsuite/latency 
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".
> == Sampling period: 1000 us
> == Test mode: periodic user-mode task
> == All results in microseconds
> [New Thread 0xb6e15470 (LWP 32035)]
> [New Thread 0xb6e0d470 (LWP 32036)]
> warming up...
> 
> Program received signal SIGILL, Illegal instruction.
> [Switching to Thread 0xb6e0d470 (LWP 32036)]
> 0xffff0f04 in ?? ()
> (gdb) where
> #0  0xffff0f04 in ?? ()
> Cannot access memory at address 0x3e0
> (gdb) list
> Cannot access memory at address 0x3e0
> (gdb) 
> 

0xffff0f04 looks like one of the kuser helpers. It is the I-pipe tsc
emulation address actually. You probably do not have access to the
architected timers in user-space. There is a snippet in
drivers/clocksource/arm_arch_timer.c to enable this access through the
CNTKCTL register. Maybe this only enables access to physical counter
whereas newer kernels use virtual counters?

-- 
                                                                Gilles.