STM8 power mode management and power consumption control

1. Power consumption control adjustment

1. Hardware function adjustment

2. Software function adjustment

3. Experience

• 3.3V power supply is more energy-efficient than 5V

• HSI saves more power than HSE

• The lower the crystal frequency, the more power it saves

• Reading and writing RAM saves more power than FLASH

• On-chip resources affect power consumption, and those not in use should be turned off using the PCG function.

2. Power Management

How to enter the mode?

Enter wait mode: asm("WFI");

Enter active shutdown mode: asm("HALT"); // Enable AWU and execute this statement to enter active shutdown mode

Entering the shutdown mode: asm("HALT"); //If AWU is not enabled, executing this statement will cause the system to enter the shutdown mode.

3. Automatic wake-up AWU structure and configuration

Automatic wake-up unit for MCU active stop mode,

1. Clock source

AWU can choose two clock sources: LSI and HSE

Selected by the "CKAWUSEL" bit in option byte OPT4:

Set to 0 ==》LSI (default);

Set to 1 ==》HSE.

2. Clock source frequency division coefficient

Select by the "PRSC[1:0]" bits in option byte OPT4:

Through the settings of steps 1 and 2, a rough clock LS is obtained.

3. Correct the clock frequency (not often used)

Use the "MSR" bit in the AWU_CSR control/status register and the input capture channel 1 of TIM3 or TIM1 to detect the clock frequency of LS. If an error is found, reconfigure APR[5:0] in the asynchronous prescaler AWU_APR to correct the timing.

4. Configure asynchronous prescaler

Configure the APR[5:0] in the asynchronous prescaler AWU_APR to configure the appropriate division value

APR: Prescaler factor

5. Write time base selection register

Write AWUTB[3:0] in the time base select register AWU_TBR to select the required automatic wake-up delay interval

AWUTB: Time interval

How to set it up?

Refer to this table:

For example, if we want to set a 6ms timing, we can find: AWUTB=0101

According to the calculation formula: 3 seconds =

Where fLS=128000, we can calculate: APR=48

Check the APR table again

Determine that APR should be assigned a value of 2E

6. Control bit enable

Set the AWUEN bit in the Control/Status Register (AWU_CSR)

7. Execute the HALT command to enter active shutdown

asm("HALT");

The four specific operations are as follows

① Turn on LSI and set the fast wake-up function at the same time. Both functions are in the CLK_ICKR register.

CLK_ICKR|=0x0C; //Turn on LSI clock and enable fast wakeup from active stop mode

② Determine whether the FLASH is powered off after entering active shutdown

FLASH_CR1&=0x0B; //Flash does not power down in active stop mode

③ Set the prescaler value

AWU_APR=0x26; //Configure pre-scaling value

④ Set the AWU wake-up time interval

AWU_TBR=0x0C; //Configure AWU wake-up time interval

⑤ Enable AWU

AWU_CSR1|=0x10; // Enable "AWUEN" to start AWU

⑥ Enter active shutdown mode

asm("HALT");

⑦ If you write an active shutdown wake-up interrupt, it will be triggered when waking up, so you should write an interrupt response function

#pragma vector=3

__interrupt void AWU_IRQHandler(void) //Automatically wake up AWU interrupt function

{  

  //Write the interrupt response function here

  AWU_CSR1|=0x10; //Continue to enable AWU

  //asm("HALT");

}

The first few steps can be written as an initialization function: AWU_init()

void AWU_init(void)

{

  CLK_ICKR|=0x0C; //Turn on LSI clock and enable fast wakeup from active stop mode

  FLASH_CR1&=0x0B; //Flash does not power down in active stop mode

  AWU_APR=0x26; //Configure pre-scaling value

  AWU_TBR=0x0C; //Configure AWU wake-up time interval

  AWU_CSR1|=0x10; // Enable "AWUEN" to start AWU

}