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. 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
