WinSystems PPM-C407, Руководство по эксплуатации продукта

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PPM-C407/Configuration
v1.0 www.winsystems.com Page 15
7.5 Watchdog Timer
The PPM-C407 features an advanced watchdog timer which can be used to guard
against software lockups. Two interfaces are provided to the watchdog timer. The
Advanced interface is the most flexible and recommended for new designs. The other
interface option is provided for software compatibility with older WinSystems single
board computers.
7.5.1 Advanced
The watchdog timer can be enabled in the BIOS Settings by entering a value for
Watchdog Timeout on the Intel > Super I/O Control screen. Any non-zero value
represents the number of minutes prior to reset during system boot. Once the operating
system is loaded, the watchdog can be disabled or reconfigured in the application
software.
NOTE Use a long timeout if the watchdog is enabled when trying to boot any operating
system.
The watchdog can be enabled, disabled, or reset by writing the appropriate values to the
configuration registers located at I/O addresses 565h and 566h. The watchdog is
enabled by writing a timeout value other than zero to the I/O address 566h and disabled
by writing 00h to this I/O address. The watchdog timer is serviced by writing the desired
timeout value to I/O port 566h. If the watchdog has not been serviced within the allotted
time, the circuit resets the CPU.
The timeout value can be set from 1 second to 255 minutes. If port 565h bit 7 equals 0,
the timeout value written into I/O address 566h is in minutes. The timeout value written
to address 566h is in seconds if port 565 bit 7 equals 1.
Watchdog Timer Examples
Port
Address
Port Bit 7
Value
Port Address Value Reset Interval
565h x 566h 00h DISABLED
565h 1 566h 03h 3 seconds
565h 1 566h 1Eh 30 seconds
565h 0 566h 04h 4 Minutes
565h 0 566h 05h 5 Minutes
Software watchdog timer PET = PORT 566h, write the timeout value.
PRELIMINARY