Hello,

On Sat, Mar 07, 2015 at 12:29:33PM +0100, Pavel Machek wrote:

On Sat 2015-03-07 12:06:45, Alexandre Belloni wrote:

quoted

On 07/03/2015 at 11:39:39 +0100, Pavel Machek wrote :

quoted

quoted

The Atmel watchdog can't be stopped once it's started. This is actually 
very useful so we can reset if suspend or resume failed, the only 
drawback is that you have to wake up from time to time (e.g. by using 
the RTC/RTT) to clear the watchdog and then go back to sleep ASAP.

Yeah. So you do "echo mem > /sys/power/state", and few seconds/minutes
after watchdog kills the system. But you did not ask for dead system,
you asked for suspend.

And while that behaviour is useful for you, I don't think it is
exactly useful behaviour, nor it is the behaviour user would expect.

I think you misunderstood, that is exactly the expected behaviour. This
is hardware defined. Once the watchdog is started, nobody can stop it.
Trying to change the mode register will result in a reset of the
SoC.

Well, it boils down to "what is stronger". Desire to suspend the
system, or desire to reboot the system.

It is "echo mem > state", not "echo reboot > state".

Maybe we should warn the watchdog is enabled and the system is going to 
reboot if nothing woke-up the system before the watchdog expire, but the 
maximum watchdog is 16s so it can't get unnoticed during development, I 
am confident embedded engineers are smart enough to understand what is 
happening without a displayed warning :-)

quoted

It is documented in the datasheet and any user wanting another behaviour
is out of luck.

Actaully, your platform should just refuse to enter suspend-to-RAM
when hw watchdog is enabled.

Yeah that's what I said, hardware watchdog or suspend: chose one or use 
the software watchdog instead or "hack" around the way I am doing ;-)


Sylvain