WatchDog Timer in Beaglebone Black

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I am using BeagleBone Black in a project and wanted to ask if anyone knows the limits of the internal WDT (WatchDog Timer). What can it and what can it not do? I'm a beginner with BeagleBone and WDT...

Thanks!

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gior91 On

Quoting from "AM335x Sitara™ Processors - Technical Reference Manual":

The watchdog timer is an upward counter capable of generating a pulse on the reset pin and an interrupt to the device system modules following an overflow condition. The watchdog timer serves resets to the PRCM module and serves watchdog interrupts to the host ARM. The reset of the PRCM module causes a warm reset of the device.

Substantially the WDT is a clock device, that is a hw. register whose value is automatically increased regularly with accurate frequency. There is also an hardware comparator whose goal is to trigger an IRQ every time the WDT overflows. The difference with a traditional timer is in the default action done on IRQ: in this case (WDT) is to reset the board.

The main goal of the WDT is to react to error situations in which the runtime environment (or the kernel) is freezed and is not responding anymore. When this happens the runtime does not reset the WDT, so it overflows, launch an IRQ and the board is resetted so that the runtime environment can regain control of the board.

To use this feature (you're obliged if you don't want your board to be resetted every x seconds) you'll have to write any value in the WDT_WTGR register (hw. address - 0x44E35030) to cause a time counter reload and avoid reset of the board. I noticed that WDT overflows after approximately 50 seconds on the Beaglebone Black, so you'll have to write a value every x < 50 seconds.

However this is valid if you plan to implement a bare metal application to be loaded on the board. In other words the WDT is correctly handled by UBoot (the BBB default boot loader) or by the Linux kernel so you'll not have to worry about this.

I hope I have taken away your doubts! :-)

Further reading: http://www.ti.com/lit/ug/spruh73m/spruh73m.pdf - section 20.4