STM32F3xx microcontroller low-power application example

AN4538

16/25

DocID026505 Rev 1

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State machine

Initially, the device is in Standby mode.

First, the user pushes the user-button to wake up the device from standby. If the user does

not push the button, the device will wake up via RTC after a pre-defined period (20 s by

default). Then, the device sends data, via the virtual comport (see Sleep1 state description).

Once the transfer is completed, the CPU enters Stop mode.

The device remains in Stop mode until the user pushes a keyboard button to transfer a

number from 1 to 4. It will simultaneously wake up the device via USART, select the desired

configuration of the comparator inverting input (Vrefint or DAC1_OUT1) and the RTC

display (yes or no).

Then, the STM32F302x8 device enters Sleep mode. In this mode, timer 1 generates the

PWM signal and the comparator is active to detect in real time when the non inverting input

voltage exceeds the chosen reference voltage (inverting input). In this case, the comparator

generates an interruption that wakes up the device from Sleep mode and stops PWM

generation via the internal signal OCref_clr.

After that, Sleep mode is entered again to send, via DMA, the data about previous state and

the log time of all states (if already enabled).

When the DMA transfer is completed, the device enters Standby mode.

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States:

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Run1: When the device is powered on, it configures the system clock and the

RTC calendar and wakeup sources.

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Standby: After power-on, the device enters Standby mode after the configuration

in Run1 is configured and remains in Standby mode until it is woken up (wakeup

pin or RTC).

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Run2: After waking up from Standby mode, configures USART, DMA to be ready

for transfer and read time.

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Sleep1: Sends a message to the user via DMA about the possible configurations

to select. Once the transfer is completed, the device wakes up from Sleep1.

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Run3: Configures the USART wakeup source to be used in Stop mode, then

reads the time.

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Stop: Remains in Stop mode until a USART data is received to wake up the

device.

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Run4: Configures and starts COMP2, TIM1 and DAC1 if used, then reads the

time.

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Sleep2: Sends a message to the user via DMA. TIM1 generates a PWM signal.

The comparator is active to compare the injected analog signal to Vrefint or

DAC1_OUT1. When a comparator interruption occurs, it wakes up the device from

Sleep mode and stops the PWM generation via OCref_clr.

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Run5: Disables TIM1, COMP2 and DAC if used, then reads the time, prepares to

display the log time profile if it is selected.

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Sleep3: Sends a message including the log time profile. Once the transfer is

completed, the device wakes up from Sleep3 mode.

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Run6: Reads the time and saves it in the backup domain. Reconfigures the RTC

before entering again Standby mode to start a new round.