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CMSIS-RTOS2
Version 2.0.0
Real-Time Operating System: API and RTX Reference Implementation
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RTX5 provides extension for tick-less operation which is useful for applications that use extensively low-power modes where the SysTick timer is also disabled. To provide a time-tick in such power-saving modes a wake-up timer is used to derive timer intervals. The CMSIS-RTOS2 functions osKernelSuspend and osKernelResume control the tick-less operation.
Using this functions allows the RTX5 thread scheduler to stop the periodic kernel tick interrupt. When all active threads are suspended, the system enters power-down and calculates how long it can stay in this power-down mode. In the power-down mode the processor and potentially peripherals can be switched off. Only a wake-up timer must remain powered, because this timer is responsible to wake-up the system after the power-down period expires.
The tick-less operation is controlled from the os_IdleThread thread. The wake-up timeout value is set before the system enters the power-down mode. The function osKernelSuspend calculates the wake-up timeout measured in RTX Timer Ticks; this value is used to setup the wake-up timer that runs during the power-down mode of the system.
Once the system resumes operation (either by a wake-up time out or other interrupts) the RTX5 thread scheduler is started with the function osKernelResume. The parameter sleep_time specifies the time (in RTX Timer Ticks) that the system was in power-down mode.
Code Example:
__WFI()
is not available at every Cortex-M implementation. Check device manuals for availability.