Re: Some embedded topics

[Wolfgang Denk <wd-ynQEQJNshbs@public.gmane.org>]

In message <200805282201.48746.rob-VoJi6FS/r0vR7s880joybQ@public.gmane.org> you wrote:
> 
> 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.

That's not theory, but a standard feature in U-Boot. It's called
shared log buffer, as U-Boot can also use this buffer for example for
POST results.

> 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.

There is no trickery involved.

Best regards,

Wolfgang Denk

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