
UG-1262
Rev. B | Page 288 of 312
CRYSTAL
OSCILLATOR
CIRCUIT
(ANALOG)
PRESCALER
32kHz
BASE CLOCK
DIGITAL
TRIM
RTC
COUNT
ALARMS
INTERRUPT
CONTROL
SNAPSHOTS/
RTC
CLOCK DOMAIN,
32kHz
32kHz TIMED
WAKE-UP IRQ TO PMU
PRESCALED, GATED
32kHz RTC TIME BASE
CLOCK
DOMAIN
CROSSING
CONTROL
POSTED
WRITE
TRANSACTION
ENGINE
INTERRUPT
CONTROL
AND STATUS
32kHz
FCLK
FCLK
PCLK
PCLK
PROCESSOR
CLOCK DOMAIN,
FCLK AND PCLK
APB
SLAVE
PORT
APB
FCLK TIMED
IRQ TO NVIC
166
75-
047
Figure 65. Digital Die WUT Block Diagram
WUT OPERATING MODES
Initial WUT Power-Up
The WUT operates in a dedicated voltage domain that is continuously powered under normal conditions. However, when a battery is
attached for the first time or replaced, a POR occurs. This POR resets all WUT registers. Upon detecting a WUT failure, the CPU
reprograms the count registers of the timers and clears the fail flag in the timer control register. The CPU can optionally program the
alarm registers of the timer to generate an interrupt when the alarm and count values match.
Persistent Sticky Wake-Up Events
When the device is in a power-down mode, there are no losses of timer alarm events. If the alarm is enabled, the resulting interrupt is
asserted by the WUT so that the NVIC subsequently sees an RCLK timed version of the interrupt when power is restored to the
processor. To facilitate this interrupt, the timer sends a 32 kHz timed version of the same interrupt to the wake-up controller in the
PMU, which causes the digital core to be repowered. When the CPU is woken up, it can inspect both the PMU and WUT to understand
the cause of the interrupt event for the wakeup.
WUT Capacity to Accommodate Posted Writes by CPU
If a posted write by the CPU to a 32 kHz sourced MMR in the WUT is pending dispatch in the WUT clock domain due to a queue of
other similar register writes to the 32 kHz domain, a second or subsequent write by the CPU to the same WUT register cannot be stacked
up to overwrite the pending transaction. Any such attempts are rejected by the WUT. These result in SR0, Bit 4 interrupt events in the
WUT (see the Status 0 Register section).
Snapshot of the Timer Counter
The CPU can instruct the timer to take a snapshot of its elapsed time count by writing a software key of 0x7627 to the GWY register.
This causes the combined three snapshot registers (SNAP0, SNAP1, and SNAP2) to update to the current value of the three count
registers (CNT0, CNT1, and CNT2) and to maintain this snapshot until subsequently told by the CPU to overwrite it.
WUT RECOMMENDATIONS: CLOCK AND POWER
Stopping the PCLK
Before entering any mode that causes the PCLK to stop, the CPU must first wait until there is confirmation from the WUT that no
previously posted writes have yet to complete. The CPU can check this by reading both the SR0 and SR2 registers.