Timer Diagram; Programming The Watchdog Timer In Timer Mode - Texas Instruments OMAP5910 Technical Reference Manual

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Figure 6–5. Timer Diagram

When the timer has been configured as a general-purpose timer, it can be

switched back to watchdog mode by writing a 1 to the watchdog bit of the

TIMER_MODE register. In this case, the value loaded into LOAD_TIM is set

to the maximum value (0xFFFF) as on power up.

In watchdog mode, the control timer register (CNTL_TIMER) must not be

used. The watchdog timer cannot be stopped by clearing the ST field. The

prescale value is 7, regardless of the PTV field value. Autoreload and one-shot

do not apply, because, if the counter underflows, the processor is reset and the

watchdog registers are reinitialized.

The timer is started by setting the ST field of the control timer register

(CNTL_TIMER) to 1. It is stopped by resetting this bit to 0. When the timer is

stopped, the content of the decrementer is frozen.

If the autoreload bit is disabled (the AR field of control timer register

(CNTL_TIMER) is 0), the timer decrements from the loaded value down to

zero and then stops. If the autoreload bit is enabled (AR = 1), the timer contin-

ues. A new value (from the load register) is loaded into the timer when it passes

though zero or when it starts. An interrupt is produced when the corresponding

timer is equal to zero.

To avoid undefined value, do not change the setting of the PTV field or the AR

field of the control timer register (CNTL_TIMER) or the LOAD_TIM register

while the timer is running. PTV can be set to values other than 7 when the

watchdog timer is in timer mode.

The timer value is held in the VALUE_TIM field of the READ_TIM register and

can be read while the timer is running or stopped.

MPU Private Peripherals

Watchdog Timer