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STR912FAW46 sleep mode

Tomas Hamouz
Associate III

Hallo all

I have troubles using sleep mode with this MCU.

In our application there is a hardware watchdog (STM6822), which should be restarted every 1 second.

I use RTC alarm feature for periodic wake-up.

The problem is that the MCU sometimes freezes and the watchdog resets the MCU.

I have tried many variants (inlined SCU_EnterSleepMode, more nops), but nothing helped reliably.

Each unit behaves differently - one change helped with one device, but worsened that in other device.

Is there something I am missing to correctly put MCU into sleep mode and reliably wake-up?

Tomas

(shortened code follows)

void __attribute__ ((section (".fast"))) sleep_mode(void) {

   (void)SCU_MCLKSourceConfig(SCU_MCLK_RTC);

   bool should_sleep = true;

   while (should_sleep) {

       watchdog_reset();

       while (rtc_hw_get_ms() > 950) {;}      // to be sure the alarm will not be missed

       rtc_set_alarm_after(WAKEUP_PERIOD);    // set alarm to nearest second

       RTC_ITConfig(RTC_IT_Alarm, ENABLE);

       WIU_ClearITPendingBit(0xFFFFFFFF);

       WIU_Cmd(ENABLE);     

       SCU_EnterSleepMode();

       __asm__ volatile ("nop\r\n nop\r\n nop");     // see Errata 2.10.1

       // here the MCU sleeps

       WIU_Cmd(DISABLE);

       rtc_clearAlarm();

       watchdog_reset();                   

       should_sleep = function_to_get_reason_for_wake_up();

   }

}

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