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Chapter 3
Watchdog Timer
The watchdog timer (WDT) restarts the system if a mishap occurs, ensuring proper start-up after the
interruption. Possible problems include failure to boot properly, the application software's loss of
control, failure of an interface device, unexpected conditions on the bus, or other hardware or software
malfunctions.
The WDT (watchdog timer) can be used both during the boot process and during normal system
operation.
• During the Boot process – If the operating system fails to boot in the time interval set in the
BIOS, the system will reset.
Enable the WDT in the Advanced BIOS Features of BIOS Setup. Set the WDT for a time-out
interval in seconds, between 2 and 255, in one-second increments in the Advanced BIOS Features
screen. Ensure you allow enough time for the boot process to complete and for the OS to boot.
The OS or application must tickle (turnoff) the WDT as soon as it comes up. This can be done by
accessing the hardware directly or through a BIOS call.
• During System Operation – An application can set up the WDT hardware through a BIOS call, or
by accessing the hardware directly. Some Ampro Board Support Packages provide an API
interface to the WDT. The application must tickle (turnoff) the WDT in the time set when the
WDT is initialized or the system will be reset. You can use a BIOS call to tickle the WDT or
access the hardware directly.
The BIOS implements interrupt 15 function 0C3h to manipulate the WDT.
• Watchdog Code examples – Ampro has provided source code examples on the LittleBoard 800
Doc & SW CD-ROM illustrating how to control the WDT. The code examples can be easily
copied to your development environment to compile and test the examples, or make any desired
changes before compiling. Refer to the WDT Readme file in the Miscellaneous Source Code
Examples subdirectory, under the LittleBoard 800 Software menu on the LittleBoard 800 Doc &
SW CD-ROM.
LittleBoard 800
Standard DB9 Serial
Port Connector (Female)
Rear View
Figure 3-3. Hot Cable Jumper
Reference Manual
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Hardware
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