On Thu, Mar 03, 2016 at 01:53:47PM +0100, Romain Izard wrote: > Hi Guenter, > > 2016-03-03 13:10 GMT+01:00 Guenter Roeck <linux@xxxxxxxxxxxx>: > > On 03/03/2016 02:29 AM, Romain Izard wrote: > >> > >> If the internal counter is not refreshed when the watchdog is started > >> for the first time, the watchdog will trigger very rapidly. For > >> example, opening /dev/watchdog without writing in it will immediately > >> trigger a reboot, instead of waiting for the delay to expire. > >> > >> To avoid this problem, reload the timer on opening the watchdog > >> device. > >> > >> Command: "while sleep 5; do echo 1; done > /dev/watchdog" > >> Before: system reset > >> After: the watchdog runs correctly > >> > >> Signed-off-by: Romain Izard <romain.izard.pro@xxxxxxxxx> > > > > > > Subject might better read "ping watchdog on start" or similar. > > > OK. I'll change it for a v2. > > > Does the watchdog have to be pinged before it is enabled ? I am a bit > > concerned that there may still be a 125 uS window during which the > > system could restart. > > > > According to the SAMA5D2 & SAMA5D4 datasheets, the timer ought to be > reloaded when the watchdog is enabled by a write in the MR register. > Unfortunately, it does not work as described, as I encountered the > problem on a SAMA5D2 Xplained board. > > The 4 clock delay is not in the datasheet either, but without any delay > the timer is clearly not reloaded, as my issue stays the same. As there > is a required delay before writing to MR after writing to CR, I applied > the same type of delay in the reverse case. > Question is if there is now a 4 clock window where the watchdog can still reset the system. Can you reload the timer before enabling the watchdog ? Thanks, Guenter > Perhaps Nicolas or Wenyou have more information on this. > > Best regards, > -- > Romain Izard -- To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
