BS_Watchdog timer
RM0082
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Doc ID 018672 Rev 1
16.3
Main functions description
16.3.1 AMBA
APB
interface
The AMBA APB interface block provides an APB slave which allows to accesses to all
registers in the watchdog module.
In particular, the lock register (WdogLock,
) controls the enabling of write
accesses to all the other registers in order to ensure software cannot unintentionally disable
the watchdog module operation.
16.3.2 Free
running
counter
The free running counter block contains the 32 bit down counter functionality (including
related registers,
), and the logic to generate the interrupt and reset signal
outputs.
The counter and the interrupt/reset logic are clocked independently, as detailed in
16.4 Clock
signals
The watchdog module uses two different input clocks:
●
The clock of the APB bus (PCLK signal), which is used to clock the Watchdog module
registers through APB bus.
●
The external WDOGCLK signal which, in conjunction with its clock enable,
WGDOGCLKEN, is used to clock the Watchdog module counter and its associated
interrupt and reset generation logic. In particular, the watchdog counter only
decrements on a rising edge of WDOGCLK when WDOGCLKEN is HIGH.
The following constraints must be observed in the relationship between the two clocks:
●
The rising edge of WDOGCLK must be synchronous and balanced with the rising edge
of PCLK,
●
The WDOGCLK frequency cannot be greater than the PCLK frequency.
From the constraints above and depending on the relationship between WDOGCLK and
WDOGCLKEN, the watchdog module counter is decremented on different ways
summarized in
.
Table 246. Watchdog module counter decremented
Clocks
WDOGCLKEN Behaviour
WDOGCLK equals PCLK
HIGH
The counter is decremented on every WDOGCLK edge
Pulsed
The counter is decremented on every second
WDOGCLK rising edge
WDOGCLK less than
PCLK
HIGH
The counter is decremented on every WDOGCLK rising
edge
Pulsed
The counter is decremented on every second
WDOGCLK rising edge