DEEPSLEEP RECORDS SOFTWARE

The WIC allows the power consumption of the processor to be further reduced by stopping all the clock signals to the processor or even putting the processor into a state retention state. The WIC is a small interrupt detection logic that mirrors the interrupt masking function in the NVIC. Otherwise the processor might enter sleep during the initialization of the processor, if an interrupt occurs during this stage.ĭesigners of microcontrollers using Cortex-M processors can optionally include a WIC Setting this bit in an interrupt driven application is usually carried out as the last step of the initialization process. The Sleep-On-Exit feature is controlled by the SLEEPONEXIT bit in the SCR. Each time the processor finishes an interrupt service routine and enters sleep, it does not have to carry out the unstacking process because it knows that these registers will have to be stacked again when another interrupt request arrives next time. The Sleep-On-Exit feature reduces the active cycles of the processor and also the energy consumed by the stacking and unstacking of processes between the interrupts. The resulting activities of the processor are illustrated in Figure 9.10.

DEEPSLEEP RECORDS SOFTWARE

For example, the software flow could be like the flow chart in Figure 9.9. This feature is useful for applications where the processor activities are interrupt-driven. When this feature is enabled, the processor automatically enters a WFI sleep mode when exiting an exception handler and if no other exception is waiting to be processed. One of the low-power features of the Cortex-M processors is called Sleep-On-Exit. In summary, the similarities and differences between WFI and WFE are shown in Table 9.14. This arrangement allows the processor to execute system management tasks (for example, restore clock to peripherals) before execute the interrupt service routine, as shown in Figure 9.8. Some of you might wonder why when PRIMASK is set, it allows the processor to wake up but without executing the interrupt service routine. The wake-up behavior of Sleep-On-Exit is same as WFI sleep. Table 9.13: WFI and WFE sleep wake-up behavior The wake-up conditions of the WFE and WFI instructions are illustrated in Table 9.13. However, in this case, the processor will not execute the interrupt handler and will resume program execution from the instruction following the WFE. The SEVONPEND feature can wake up the processor from WFE sleep even if the priority level of the newly pended interrupt is at the same or lower level than the current interrupt. WFE can also be woken up by interrupt requests if they have a higher priority than the current interrupt’s priority level, or when there is a new pending interrupt request and the SEVONPEND bit (Send event on pending) is set. Therefore usually the WFE is used in an idle loop or polling loop as it might or might not cause entering of sleep mode. The event latch inside the processor can hold an event which happened in the past, so an old event can cause the processor to wake up from a WFE instruction. If the SEVONPEND (Send-Event-On-Pend) feature is enabled and a new pending interrupt occursĮxecution of the SEV (Send Event) instruction An interrupt request arriving which needs servicingĪn external event signal from on-chip hardware (device specific)

Deepsleep records