Re: Some embedded topics

["Mike Frysinger" <vapier.adi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Wed, May 28, 2008 at 11:01 PM, Rob Landley wrote:
> On Tuesday 27 May 2008 17:31:42 T Ziomek wrote:
>> If I understand correctly David is talking about logging some trace-like
>> info (so it exists before a HW watchdog expires), and having it somewhere
>> "safe" from being disturbed by a HW reset.
>
> The standard way of doing this is to use the mem= kernel command line
> parameter to tell the system it has less memory than it does, and using
> what's left as a ramdisk.  Years ago I saw some userspace thing running as
> root mmap() /dev/mem (or whatever they're calling it these days) and log to
> it.  In theory you could even set the dmesg buffer up at the end of physical
> memory with a smallish kernel patch, make it big, and set the kernel to doing
> verbose printks.
>
> The trick is A) knowing the absolute physical address at which your debug
> buffer lives so you can find it after the reboot, B) convincing the system to
> do something useful with it on reboot rather than just overwriting it with
> fresh log data.

how about the fact that when the core resets, the memory controller is
often reset as well ?  that external memory is going to degrade.  or
do we just bite our thumb and weather the few random bit errors ?
-mike
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