Consequences of not restoring the clock when waking up from STM32 stop mode-EEWORLD

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For a detailed analysis of STM32's low power consumption, please refer to the interpretation of STM32's low power consumption mode . It is mentioned that when STM32 is in stop mode, the chip's 1.8V area clock is turned off, and the HSI and HSE clocks are also turned off. When an enabled interrupt or event occurs, STM32 exits from stop mode. At this time, the default clock of STM32 is HSI. Therefore, if you want to return STM32 to run mode and work normally for a period of time, you must pay attention to the clock problem of STM32 and choose whether to restore the system clock to the clock configuration before stop mode according to the actual situation.

The chip used in the test is stm32fo30, the HSI clock frequency is 8M, the system frequency is 48M, the PLL multiplication is 12, and the input is HSI/2.

Test the influence of LED lighting time

The systick timer is used for timing. When the button is pressed, the LED lights up and the timer starts timing for 5 seconds. When the timing is up, the LED goes out.

In normal mode, the LED lights up for 5 seconds.

After waking up from stop mode, the system clock is not restored and the LED light turns off after 30 seconds.

Analysis: The system frequency is 6 times the HSI frequency, so the LED lighting time also satisfies the 6-fold relationship.

After waking up from stop mode, the system clock is not restored and the LED light turns off after 30 seconds.

After waking up from stop mode, the system clock is restored and the Timer 5 LED is off.

Test 2, serial port

In normal mode, the serial port can send and receive normally.

After waking up from stop mode, the system clock is not restored, the serial port receives a bunch of garbled characters, and normal data cannot be received. Reason:

The serial port clock is set to the system clock, resulting in a baud rate mismatch.

After waking up from stop mode, the system clock is restored and the serial port reception and transmission are normal.

Summary: Pay special attention to the clock recovery configuration after the STM32 wakes up from stop mode to prevent various minor problems.

Keywords：STM32 Reference address：Consequences of not restoring the clock when waking up from STM32 stop mode

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