os_suspend

#include <rtl.h>

U32 os_suspend (void);

The os_suspend function suspends the OS task scheduler. The function calculates the time, for how long the system is allowed to power-down, and locks the task scheduler. When the function returns, the task switches are disabled. For the normal RTX operation, after calling os_suspend, you must call the os_resume function to re-enable the OS task scheduler.

The os_suspend function is in the RL-RTX library. The prototype is defined in rtl.h.

Note

• This function is used in Low Power RTX applications.
• You can call this function from the idle task only.
• When the system is in power-down, the system tick timer is not running.

The os_suspend function returns the number of ticks, for how long the system can sleep or power-down.

os_resume

#include <rtl.h>

__task void os_idle_demon (void) {
  uint32_t sleep;

  SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;    /* Configure Cortex-M3 for deep sleep */
  PWR->CR &= ~PWR_CR_PDDS;              /* Enter Stop mode when in deepsleep  */
  PWR->CR  |= PWR_CR_LPDS;              /* Voltage regulator in low-power     */

  /* Enable LSI clock and wait until ready */
  RCC->CSR |= RCC_CSR_LSION;
  while ((RCC->CSR & RCC_CSR_LSIRDY) == 0);

  /* Enable power interface clock */
  RCC->APB1ENR |= RCC_APB1ENR_PWREN;

  /* Disable backup domain write protection */
  PWR->CR |= PWR_CR_DBP;

  /* Select LSI as clock source for RTC and enable RTC */
  RCC->BDCR &= ~RCC_BDCR_RTCSEL;
  RCC->BDCR |=  RCC_BDCR_RTCSEL_1;
  RCC->BDCR |=  RCC_BDCR_RTCEN;

  /* Disable the write protection for RTC registers */
  RTC->WPR   = 0xCA;
  RTC->WPR   = 0x53;

  /* Configure RTC auto-wakeup mode */
  RTC->ISR  &= ~RTC_ISR_WUTF;           /* Clear wakeup timer flag            */
  RTC->CR   &= ~RTC_CR_WUCKSEL;         /* Set RTC clock to 2kHz              */
  RTC->CR   |=  RTC_CR_WUTIE;           /* Enable RTC wakeup timer interrupt  */

  /* Configure EXTI line 22 for wakeup on rising edge */
  EXTI->EMR  |= (1 << 22);              /* Event request is not masked        */
  EXTI->RTSR |= (1 << 22);              /* Rising trigger enabled             */

  NVIC_EnableIRQ (RTC_WKUP_IRQn);       /* Enable RTC WakeUp IRQ              */

  for (;;) {
    /* HERE: include optional user code to be executed when no task runs.     */
    sleep = os_suspend ();              /* OS Suspend                         */

    if (sleep) {
      RTC->ISR &= ~RTC_ISR_WUTF;        /* Clear timer wakeup flag            */
      RTC->CR &= ~RTC_CR_WUTE;          /* Disable wakeup timer               */
      while ((RTC->ISR & RTC_ISR_WUTWF) == 0);

      /* RTC clock is @2kHz, set wakeup time for OS_TICK >= 1ms */
      RTC->WUTR = (sleep * (OS_TICK / 1000) * 2);

      RTC->CR |=  RTC_CR_WUTE;          /* Enable wakeup timer                */
      __WFE ();                         /* Enter STOP mode                    */

      /* After Wake-up */
      if ((RTC->ISR & RTC_ISR_WUTF) == 0) {
        sleep = 0;                      /* We didn't enter Stop mode          */
      }
    }
    os_resume (sleep);                  /* OS Resume                          */
  }
}