syslog basic querry
Wolfgang Denk
wd at denx.de
Wed Dec 28 09:05:53 UTC 2005
Dear Alfred,
in message <29f916510512271831x5e822bet68cbca3382bfd779 at mail.gmail.com> you wrote:
>
> Thanks for tip on unchanged-stats, it's exactly what I was looking for.
> May be i will patch busybox tail for it, should be helpful patch IMHO.
I'm glad I was able to help.
> pramfs from it's web page looked like meant for NVRAM based logging ?
If you have NVRAM then a pramfs file system can survive even a power
failure. If you just have to deal with crashes / resets / reboots
(including such resets that are initiated by a hardware watchdog)
then you can use a reserved area in system RAM to create a pramfs
file system - the data will be available as long as power is supplied
to the system.
> I didnt quite fully get u-boot thing you pointed.
U-Boot supports a log buffer (allocated typically at the end of
physical RAM) which uses the same format and data structures like the
Linux syslog buffer. With a small patch to the Linux kernel this log
buffer can be preserved and used by Linux, too (instead of allocating
a new buffer). That means that:
1 - you can use standard Linux syslog facilities to read and process
log messages (like results from your POST code) created by the
boot loader
2 - you can read the Linux syslog buffer after a reset / crash from
U-Boot
> If I understand it well, that you are saying that u-boot can be told
> to leave out an area of RAM (from clearing / init'ing it ?) ? and so
> memory snapshot will be retained across boots ?
Correct.
> This should work across processor generated resets .. But, will it
> fail if say there has been an external reset pin triggered. External
> button reset will send reset / power cycle not only processor but also
> all peripherals ?
Reset is fine, no matter if it's caused by a soft reboot or a hard
reset. You will lose the log buffer when power cycling, though.
Best regards,
Wolfgang Denk
--
Software Engineering: Embedded and Realtime Systems, Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
Witch! Witch! They'll burn ya!
-- Hag, "Tomorrow is Yesterday", stardate unknown
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