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NEC MPI4E RaspberryPi 4 System on a Chip Solution

Raspberry Pi Compute Module Setup Guide - Page 40

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©2021 Sharp NEC Display Solutions, Ltd. Page 40 of 86
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set_system_to_display_clock.py - Reads the display’s internal clock via the internal
serial connection and sets the system time accordingly. This file can be added to a startup script
on the system, if necessary, to set the OS time from the display if no network connection is
available.
•
set_display_to_system_clock.py - Sets the display’s internal clock based on the current
system time on the Compute Module.
See the files included in the SDK for more details. See Python Based NEC PD SDK on page 65.
5.12 Using the display’s Watchdog Timer (WDT)
The display features an internal Watchdog Timer that can be used to automatically restart the Compute
Module if it stops responding; for example, if it hangs for some reason.
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 are not
received as expected the display will send a reset signal to 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 three consecutive reset commands are not received, the
display will send a reset signal to 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
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 three consecutive
reset commands are missed, the display will restart the Compute Module.
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