AM335x: Detect if watchdog is running

Hi Rostislav,

You could read the WDT_WSPR register. If it returns XXXX 5555h the watchdog is disabled, if it returns XXXX 4444h the watchdog is enabled. See section 20.4.3.8 and 20.4.4.1.12 in the AM335X TRM Rev. K.

Hello Biser;
Thanks for the reply. I considered this option, but what about the watchdog that is enabled right after boot of the device? The bootloader/firmware may only periodically "reset it" and my application started afterwards will read "0" (as the reset value) from the WDT_WSPR as it is the "value after reset".

Best regards;
Rostislav

WD is enabled by ROM code. It's stopped early in the MLO section of u-boot by the AAAA 5555 sequence. After that default AM335X Linux does not use it.

Can I rely on the information, that the ROM code enables the watchdog with the standard "BBBB 4444" -- thus the reset value (i.e. 0) of the WDT_WCRR will be never read by the firmware/bootloader?

Best regards;
Rostislav

Yes, there is no other way to enable the WD.

Well, I tried to implement this however it does not work. During the clock initialization in Linux, the watchdog clock is probably reset (which causes the WD reset), thus the WDT_WSPR register holds the value of "0" :-(

According to this findings, there is no way how to determine if the watchdog is running or not.

Best regards;
Rostislav

If WDT_WSPR register holds the value of "0" then obviously the WDT is reset and not running.

Of course it is possible that I did something wrong, however the watchdog runs, but the value of WDT_WSPR is read as "0".

Lets imagine the scenario, someone enables the watchdog by writing the "start sequence", at first it writes (into WDT_WSPR) 0xXXXX BBBB, then 0xXXXX 4444 -- this enables the watchdog. However it also accidentally writes some garbage into the same register (lets say 0x1234 5678) -- this should have no effect.

If I read the value of the WDT_WSPR, what will I read? The last value stored?

Thanks;