[NUC980] Enabling Watchdog Timer on NUC980

The NUC980 series supports a hardware watchdog timer (WDT), which can be used to improve system robustness by resetting the system in the event of a software fault. However, the method of enabling the WDT differs depending on the chip package.

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Hardware Pin Limitation (PG3)

• LQFP128 & LQFP216: Has a PG3 pin which can be used to configure whether the watchdog is enabled during boot via hardware.
• LQFP64: Does not have PG3 — therefore, watchdog must be enabled via software (U-Boot).
  

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Enabling WDT in U-Boot (for LQFP64 or software control)1. Configure U-Boot to Enable NUC980 Watchdog Driver

$ make uboot-menuconfig

Navigate to:

Device Drivers --->  

NUC980 Watchdog

Save and exit.

2. Rebuild U-Boot$ make uboot-rebuild
$ make

After this, U-Boot will include the NUC980 watchdog support.

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Controlling WDT Activation via env.txt

In your U-Boot environment file (env.txt), add one of the following:

• To disable WDT at boot:
  

watchdog=off # or watchdog=0

• To enable WDT at boot:
  

watchdog=on # or watchdog=1 # or any non-zero, non-off string

If watchdog is undefined or set to any value other than off or 0, the watchdog timer will be enabled.

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Default Timeout Behavior

By default, the watchdog configuration in U-Boot uses the following:

• Clock source: PCLK2 / 4096
• Timeout count: 1,000,000 ticks
  

Given:

• PCLK2 = 75 MHz
• WDT clock = 75,000,000 / 4096 ≈ 18,310.5 Hz
• Timeout = 1,000,000 / 18,310.5 ≈ 54.6 seconds
  

You may modify this behavior in the U-Boot source if needed:

buildroot/output/build/uboot-custom/drivers/watchdog/nuc980_wdt.c

Reference:
https://github.com/OpenNuvoton/NUC970_U-Boot_v2016.11/blob/master/drivers/watchdog/nuc980_wdt.c

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Linux Kernel Consideration

If WDT is enabled by U-Boot, the Linux kernel must either:

• Periodically reset the watchdog timer during boot and runtime, or
• Disable the watchdog timer once the kernel is up and running.
  

Since the WDT was software-activated, it can also be cleanly disabled by the Linux kernel.

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Documentation Reference

• Watchdog Register Map: Refer to the Watchdog Timer chapter in the [NUC980 Technical Reference Manual (TRM)].
• WDT Control in U-Boot: Refer to U-Boot driver source linked above.
  

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If you need help with modifying the timeout behavior or integrating WDT into your Linux application, please let us know.