ADLINK Technology NuPRO-860 Series, Руководство пользователя

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Watchdog Timer 39
5 Watchdog Timer
The operation of the NuPRO-860’s Watchdog Timer is described
in this chapter. An overview of the watchdog operation and fea-
tures, as well as the programming procedure is provided to give
the user an insight into the workings of the Watchdog Timer.
5.1 WDT Overview
The primary function of the Watchdog Timer is to monitor the
NuPRO-860’s operation and to generate an IRQ or to reset the
system should the software fail to function as programmed. The
major features of the Watchdog Timer are:
X
Enabled and disabled through software control
X
Armed and strobed through software control
The NuPRO-860’s custom Watchdog Timer circuit is integrated
into the south bridge 6300ESB and supports multiple modes: WDT
and free-running. Free-running mode is a one stage timer and it
will toggle WDT_TOUT# after a programmable time. WDT mode is
a two stage timer and its operation is described as follows:
WDT Mode:
The two-stage Watchdog Timer (WDT) provides a resolution
ranging from 1 micro second to 10 minutes. The timer uses a
35-bit down-counter. The counter is loaded with the value from
the first Preload register. The timer is then enabled and starts
counting down. The time at which the WDT first starts counting
down is called the first stage. If the host fails to reload the WDT
before the 35-bit down counter reaches zero the WDT gener-
ates an internal interrupt. After the interrupt is generated, the
WDT loads the value from the second Preload register into the
WDT’s 35-bit down-counter and starts counting down. The
WDT is now in the second stage. If the host still fails to reload
the WDT before the second timeout, the WDT drives the
WDT_TOUT# pin low. The WDT_TOUT# pin is held low until
the system is reset.