Re: [microblaze-uclinux] Power-fail handling

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Jim,

Jim Law wrote:

> We have a SystemAce CardFlash with a single FAT partition.  Our custom 
> board gives an interrupt when the AC power begins to fail, allowing us 
> at least 20ms of time before on-board power begins to go away.  I'm 
> trying to find a reliable way to flush anything that might be in 
> uClinux's buffers to the CardFlash when we get that interrupt. 
>  
> I believe sync() does what we want, but I'm having issues getting there 
> fast enough.  We catch the power fail interrupt just fine.  Then we 
> throw a signal that gets caught by a handler in our application.  Our 
> application priority has been set so we catch the signal reliably 
> quickly in the handler, and so far we're running less than 1ms into our 
> available time. 
>  
> But it seems like the call to sync() does not return reliably 
> in the time available, even if we know there is nothing pending to write 
> to the CardFlash.
>  
> I don't know if I've chosen a silly way of doing this, or if there is 
> some other side-effect or function of sync() that might be taking the time.

You might try calling emergency_sync() directly from your interrupt 
handler in the driver, that's how they do it in e.g. drivers/char/sysrq.c

Your driver will have to #include <linux/fs.h> to get the function 
prototype.

Let us know if this helps, it's a useful capability.

Cheers,

John

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