NI Linux RT Watchdog Reset vs Normal Reboot

Updated Jul 30, 2026

Reported In

Hardware

  • PXI Controller

Operating System

  • LabVIEW Real-Time (NI Linux Real-Time)

Issue Details

I have a PXIe system running NI Linux Real-Time with a counter output configured on PFI0. When the Real-Time Watchdog restarts the system, PFI0 transitions high regardless of its state before the reset. The line remains high after the restart.
If I restart the controller manually through MAX or SSH, the same PFI line transitions low during the reboot process.
I expect the PFI line to return to a low state whenever the system resets. Why do watchdog-initiated and manual restarts result in different PFI line states?

Solution

The observed behavior is expected.
A Real-Time Watchdog restart performs a soft restart of the controller. During this type of restart, the chassis does not completely remove power from all internal supply rails. As a result, trigger and PFI lines can be pulled high by onboard pull-up circuitry.
A manual controller restart performs a hard reset. During a hard reset, the trigger and PFI lines transition low as the system powers down and reinitializes.

Related Links

RT Watchdog - LabVIEW Real-Time Module Programming Reference Manual

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