On 22/01/13 13:47, Bas Laarhoven wrote:
> On 22-1-2013 13:36, Yishin Li wrote:
>> 從我的 iPhone 傳送
>>
>> Bas Laarhoven <s...@xs4all.nl> 於 2013/1/22 下午8:07 寫道:
>>
>>> On 21-1-2013 22:20, Michael Haberler wrote:
>>>> Am 21.01.2013 um 20:10 schrieb Gilles Chanteperdrix:
>>>>
>>>>> On 01/21/2013 02:32 PM, Michael Haberler wrote:
>>>>>
>>>>>> Am 21.01.2013 um 12:56 schrieb Gilles Chanteperdrix:
>>>>>>>> question: does a RTC time warp have any possible bearing on
>>>>>>>> Xenomai operations?
>>>>>>> No, it should not, Xenomai uses its own clock, which is set only
>>>>>>> once upon boot, so, is unaffected by Linux wallclock time
>>>>>>> changes... or should be.
>>>>>> it might not be Xenomai after all. Uhum.
>>>>>>
>>>>>> the bughunt safari tribe has decided to focus on class 'duh' problems
>>>>>> and resolves to shut up until red hands are spotted.
>>>>> I would still put the check in the timer "set_next_event" callback, just
>>>>> in case...
>>>> I assume Bas will give the postmortem shortly - he nailed the issue; the 
>>>> RTC boot timewarp makes for a lost DHCP lease midflight and NFS freezing, 
>>>> making it look like a kernel hang.
>>>>
>>>> relieved,
>>>>
>>>> - Michael
>>> Michael said it all, there's not much for me to add. I'll summarize the
>>> case for the records ; )
>>>
>>> Lesson learned: Change only one variable at a time and don't assume
>>> anything!
>>>
>>> I had been using a NFS mounted filesystem with the Beaglebone for over a
>>> year now without problems and got used to it's reliability (as I was
>>> used to in a corporate environment in the past).
>>> Because the Xenomai software was built with libraries (eabihf) not
>>> compatible with my (eabi) system I switched to the Ubuntu image Michael
>>> built, and everything seemed to work fine. Except that the (xenomai)
>>> kernel froze out after around 50-60 minutes of uptime. With the JTAG
>>> debugger I could see the kernel still running, but all applications
>>> (both text and X via SSH, and console via serial/USB connection) seemed
>>> frozen and there was no output indicating what was going on. Of course
>>> the xenomai kernel was the first suspect. But that proved to be a
>>> mistake. With hindsight, knowing the cause of the freeze now, I wonder
>>> why I haven't gotten the NFS connection time-out message on the console,
>>> but for some reason or another that isn't generated in this case.
>>>
>>> The underlying problem is that the Beaglebone has no battery backed
>>> real-time clock. This gives (only) a serious problem (freeze) with (1) a
>>> network mounted NFS root filesystem and (2) an initial kernel time lying
>>> in the past and (3) a DHCP lease time shorter than some multiple (in
>>> this case 2x) of the required system uptime.
>>>
>>> Ubuntu (and maybe Debian too) systems are obviously not designed to
>>> start with a completely wrong real-time clock value. And the dhclient
>>> (as many other programs) is not designed to handle the large time step
>>> that's generated once the clock is set properly sometime during the boot
>>> process.
>>> Note that if the filesystem is on local storage (e.g. FLASH or
>>> harddisk), there will only be a short disruption of the network
>>> connection and it's likely that the problem won't be noticed at all.
>>>
>>> A final solution hasn't been found yet: I prefer a workaround without
>>> changing the dhclient or some other standard program. I think it would
>>> suffice to acquire a new lease right after the time-step has been made.
>>> This has to be done without giving up the previous lease (that has
>>> expired because of the time-step), because that would cause the system
>>> to freeze again. Suggestions on how to do this are welcome. I can't
>>> spend much more time on this issue this week.
>>>
>>> -- Bas
>> How about using static IP for NFS mounted rootfs?
> If you're not using DHCP this problem shouldn't affect you.
>
> -- Bas
>> -Yishin
>>
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ok i dont mind being shot down in flames , but would adding a RTC module 
be a answer
for example :-)

http://www.ebay.co.uk/itm/New-Arduino-I2C-RTC-DS1307-AT24C32-Real-Time-Clock-Module-For-AVR-ARM-PIC-/170794819927?pt=UK_BOI_Electrical_Comp

although i must admit it ends up having all sorts of a rats nest for now 
, and if theirs no other answer
and we end up making an interface for the Beagle the it could be more 
permamant

i mention the above rtc only for the fact that i have one laying around




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