UM0851 datasheet(212/245 Pages) STMICROELECTRONICS

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Miscellaneous device drivers

UM0851

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Doc ID 16604 Rev 2

watchdog is intended to be used to generate a system reset if a software failure (or a system

hang) occurs.

The main features of the watchdog module are listed below

●

32-bit down counter with a programmable timeout interval

●

Interrupt generation on timeout

●

Reset signal generation on timeout, if the interrupt from the previous timeout remains

pending (not serviced)

●

Lock register to protect registers from being altered by runaway software

Figure 59.

WDT interface

The down counter is driven by the WDT clock, which is the oscillator clock, 30 MHz in

SPEAr600 and 24 MHz in SPEAr3xx.

9.2.2

Software overview

The watchdog driver for SPEAr in the Linux support package is part of standard Linux

watchdog framework. Watchdog drivers in Linux are based on character device using misc

device layer and provide a standard set of ioctls to the user. Through this interface you can

configure, program and refresh the watchdog timer. You can use the standard Linux

watchdog daemon to configure and periodically pat (refresh) the driver in order to avoid

system reset. A software crash or hang would thus prevent this pat from happening and

hence cause a system reset after timeout.

The following figure describes the watchdog framework.

Watchdog timer

Load register

Control

32-bit down counter

Interrupt and reset generation

APB

interface

WDT clock

WDT interrupt

WDT reset

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