RM0440 Rev 4 1941/2126
RM0440 System window watchdog (WWDG)
1943
As an example, lets assume APB frequency is equal to 48 MHz, WDGTB[2:0] is set to 3 and
T[5:0] is set to 63:
Refer to the datasheet for the minimum and maximum values of the t
WWDG
.
43.3.5 Debug mode
When the device enters debug mode (processor halted), the WWDG counter either
continues to work normally or stops, depending on the configuration bit in DBG module. For
more details refer to Section 48.16.2: Debug support for timers, RTC, watchdog, bxCAN
and I
2
C.
43.4 WWDG interrupts
The early wakeup interrupt (EWI) can be used if specific safety operations or data logging
must be performed before the actual reset is generated. The EWI interrupt is enabled by
setting the EWI bit in the WWDG_CFR register. When the down-counter reaches the value
0x40, an EWI interrupt is generated and the corresponding interrupt service routine (ISR)
can be used to trigger specific actions (such as communications or data logging), before
resetting the device.
In some applications, the EWI interrupt can be used to manage a software system check
and/or system recovery/graceful degradation, without generating a WWDG reset. In this
case, the corresponding interrupt service routine (ISR) has to reload the WWDG counter to
avoid the WWDG reset, then trigger the required actions.
The EWI interrupt is cleared by writing '0' to the EWIF bit in the WWDG_SR register.
Note: When the EWI interrupt cannot be served, e.g. due to a system lock in a higher priority task,
the WWDG reset is eventually generated.
43.5 WWDG registers
Refer to Section 1.2 on page 72 for a list of abbreviations used in register descriptions.
The peripheral registers can be accessed by halfwords (16-bit) or words (32-bit).
43.5.1 WWDG control register (WWDG_CR)
Address offset: 0x000
Reset value: 0x0000 007F
t
WWDG
1 48000⁄()4096 2
3
×× 63 1+()× 43.69ms==
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res. Res.
1514131211109876543210
Res. Res. Res. Res. Res. Res. Res. Res. WDGA T[6:0]
rs rw rw rw rw rw rw rw
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