Black Pill: Timer interrupt every 1 second problem

[Sansan141267]

Hi,

Am using blackpill with F411 mcu at 100MHz, with Timer1 configuration:

Clock source: internal clock

Prescaler: 9999

Counter period: 9999

So Timer1 ticks every 1 second (1Hz)

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{
  secEllapsed++;   // volatile uint16_t variable
}

In main body

while (1)
{
  /* USER CODE END WHILE */

  /* USER CODE BEGIN 3 */
  sprintf(strLCD, "%6d seconds", secEllapsed);
  i2c_lcd_SetCursor(0, 0);
  i2c_lcd_PrintStr(strLCD);
}

But the result is about 24 seconds less every 10 minutes.

So what is the problem?

---

Edited to apply source code formatting - please see How to insert source code for future reference.

[mfgkw]

24 s / 10 min is just 4%. That's ok for internal clock...

But could be better. Maybe your I2C delays the Timer 1 interrupts

[Andrew Neil]

welcome to the forum

Please see How to write your question to maximize your chances to find a solution for best results.

Note that Black (and other coloured) Pill boards are not ST products, and likely do not contain a genuine STM32.