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• Wakeup source programmed in [AON_EVENT:AUXWUSEL] (including RTC channel 2).
To clear an AUX wakeup source, the sensor controller or system CPU must clear it through writing to
[AUX_WUC:WUEVCLR]. A power-down request should not be done before the flag is read as 0.
RTC channel 2 and software events from AON have dedicated clear bits. Any wakeup I/O events on pins
routed to AUX will be cleared by writing to [AUX_WUC:WUEVCLR:AON_PROG_WU].
A use case needing special handling could be when both an I/O and RTC channel 2 are used as AUX
wakeup sources and event vectors for the sensor controller.
If the RTC event occurs while the sensor controller is handling a task triggered by an I/O event, the flag
[AUX_WUC:WUEVFLAGS:AON_WU_PROG] will not go low when clearing it in the I/O wakeup handler,
because it includes the RTC event. This can be overcome in software by checking if the flag
[AUX_WUC:WUEVFLAGS:AON_RTC_CH2] is set, and running a SLEEP instruction to restart at the RTC
vector, instead of waiting for the AON_WU_PROG bit to be cleared.
Other wakeup events programmed in [AON_EVENT:AUXWUSEL] must be cleared at the source module
in AUX, or by the system CPU.
NOTE: Waking up the AUX domain will not make the sensor controller start running its program
again, as this is dependent on the state of the sensor controller. Refer to Section 17.4.1.7,
Running a Program and Section 17.4.9.6, Interrupts and Events.
17.5.4 MCU Bus Connection
Because the system CPU cannot read this register after the bus is disconnected, it must use the
[AON_WUC:PWRSTAT:AUX_PD_ON] register field to check if AUX is connected to the MCU system bus.
17.6 Clock Management
17.6.1 System Clocks
As AUX is a slave to the system CPU, the system clock for AUX is controlled by the system CPU through
the AON wakeup controller [AON_WUC:AUXCLK].
The controller configuration is tied to the power mode it is currently in.
17.6.1.1 Active Mode
In active mode, AUX runs on the high-frequency system clock (SCLK_HF), divided down by a factor
between 2 and 256 and configured by writing to the [AON_WUC:AUXCLK:SCLK_HF_DIV] register.
AUX can override this setting and run with the low-frequency system clock as source instead, by
requesting this mode by doing a four-phase handshake with the AON wakeup controller:
1. Set [AUX_WUC:CLKLFREQ:REQ] high.
2. Wait for [AUX_WUC:CLKLFACK:ACK] to go high.
3. Set [AUX_WUC:CLKLFREQ:REQ] low.
4. Wait for [AUX_WUC:CLKLFACK:ACK] to go low.
After this handshake, AUX will always use the low-frequency clock in active mode.
1210
AUX – Sensor Controller with Digital and Analog Peripherals SWCU117A–February 2015–Revised March 2015
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