Comtrol DeviceMaster ATS-XPE, Руководство по установке и настройке

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Appendix E. Changing the WatchDog Timer 91
Appendix E. Changing the WatchDog
Timer
The hardware watch-dog timer is not supported by the installed Linux kernel.
However, it may be accessed directly by user applications if desired.
The Watch-Dog Timer is a device used to ensure that standalone systems can
reset themselves and recover from catastrophic conditions that cause the CPU to
hang or crash. The Watch-Dog Timer is a countdown timer that will reset the CPU
when it times out.
The Watch-Dog Timer is enabled by reading port
443H
. It should be triggered
before the time-out period ends, otherwise it will assume that the program
operation is abnormal and will issue a reset signal to restart, or activate NMI to
CPU.
The Watch-Dog Timer is disabled by reading port 843H .
Note: Bold text (shaded green in the online version) illustrates the default value.
Three I/O ports control the Watch-Dog Timer and are accessed using the
addresses defined in the following table.
Prior to enabling the Watch-Dog Timer, the user has to define the time interval to
be used. The timer interval is defined by writing a value to address 443H. This
value is within the range from 01 (hex) to FF (hex) and defines an interval
between 1 second to 255 seconds, respectively. The following table illustrates this
correlation:
JP4 Watch-Dog Timer Settings Description
1-2 Activate NMI to CPU when WDT times-out.
2-3 Reset when WDT time-out.
Open Disable WDT.
Hex Address Read/Write Description
443H Write Set Watch-Dog Time period
443H Read Enable and refresh the Watch-Dog Timer.
843H Read Disable the Watch-Dog Timer.
Hex Value Time Interval
01 1 sec
02 2 sec
03 3 sec
04 4 sec
.
.
. .
.
.
FF 255 sec