NEC C751Q Setup Manual page 40

To use this feature, a background application is configured to periodically send reset commands to the
display via the internal UART. The display will expect to receive these reset commands as an indication
that the Compute Module is functioning normally. If, for some reason, the reset commands aren't received
as expected the display will shut down and restart the Compute Module.
Use of the Watchdog Timer is optional and requires configuring the Operating System to start the
background application at bootup. The Watchdog Timer is enabled and configured via the OSD or
communications commands. The background application must send the reset command at least as often
as the Period Time configured via the OSD. If two consecutive resets commands aren't received, the
display will restart the Compute Module.
There are two time periods that can be configured for the Watchdog Timer:
Start Up Time – This sets the time delay for when the display should start receiving WDT reset
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commands, via the internal UART, after power is applied to the Compute Module.
This timer's value should be set high enough to include time for the operating system to fully
load on the Compute Module, and for the periodic reset commands to begin sending to the
display.
• Period Time – This sets the maximum amount of time within which the display must receive
WDT reset commands from the Compute Module, via the internal UART. If two consecutive
reset commands are missed, the display will restart the Compute Module.
This timer's value should be set high enough to ensure that any software running on the
Compute Module will be able to send the periodic reset command to the display, even under
heavy load conditions.
The Python SDK includes support for sending the Watchdog Timer reset commands to the display, as
well as configuring the timer settings. See the example file reset_display_wdt.py included in the
SDK for more details. See Python Based NEC PD SDK on page 63.
See sections 8.9 through 8.11 for details on configuring the Watchdog Timer settings via the OSD.
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