stm32f405 help for timer seconds counter

[Angelo1]

Posted on April 01, 2014 at 18:47

Dear,

i need to implement a timer, with seconds step, just as a watch. I have now the follwing clock (internal) set static void SetSysClock(void) {         /* PLL (clocked by HSI) used as System clock source */         /* Select regulator voltage output Scale 1 mode,          * System frequency up to 168 MHz */         RCC->APB1ENR |= RCC_APB1ENR_PWREN;         PWR->CR |= PWR_CR_VOS;         /* HCLK = SYSCLK / 4*/         RCC->CFGR |= RCC_CFGR_HPRE_DIV4;         /* PCLK2 = HCLK / 2*/         RCC->CFGR |= RCC_CFGR_PPRE2_DIV2;         /* PCLK1 = HCLK / 4*/         RCC->CFGR |= RCC_CFGR_PPRE1_DIV4;         /* Configure the main PLL */         RCC->PLLCFGR = PLL_M | (PLL_N << 6) | (((PLL_P >> 1) -1) << 16) |                  (RCC_PLLCFGR_PLLSRC_HSI) | (PLL_Q << 24);         /* Enable the main PLL */         RCC->CR |= RCC_CR_PLLON;         /* Wait till the main PLL is ready */         while((RCC->CR & RCC_CR_PLLRDY) == 0)         {         }         /* Configure Flash prefetch, Instruction cache, Data cache and wait state */         FLASH->ACR = FLASH_ACR_ICEN |FLASH_ACR_DCEN |FLASH_ACR_LATENCY_5WS;         /* Select the main PLL as system clock source */         RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));         RCC->CFGR |= RCC_CFGR_SW_PLL;         /* Wait till the main PLL is used as system clock source */         while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS ) != RCC_CFGR_SWS_PLL);         {         } } From here, can i have a 1 second interrupt ? Ciao Angelo

[Tesla DeLorean]

Posted on April 01, 2014 at 19:22

Ok, so timers need a basic grasp of math, specifically factors, and ones that fit within certain number spaces. There are often many solutions.

For example with a 168,000,000 Hz TIMCLK (APB2) you are trying to get 1 Hz 168,000,000 / 1 = 168,000,000 16800 * 10000 = 168,000,000 (Note both fit in 16-bit) Prescaler = 16800 - 1; // TIM ticks at 10000 Hz (10 KHz) Period = 10000 - 1; // TIM rolls over at 10000 ticks @ 10 KHz, So 1 Hz, 1 Second Update Interrupt at 1 Hz For an 84 MHz TIMCLK (APB1) 8400 * 10000 = 84,000,000 Prescaler = 8400 - 1; Period = 10000 - 1; Update Interrupt at 1 Hz For 10 Hz, I could use Prescaler = 840 - 1; Period = 10000 - 1; or Prescaler = 8400 - 1; Period = 1000 - 1; 8400 * 1000 = 8,400,000 and 84,000,000 / 10 = 8,400,000

[chen]

Posted on April 02, 2014 at 10:10

Hi

I was curious what your reply would be clive1. Would the RTC not be a better solution? I know it can generate an alarm IRQ. Not sure if this is one shot only or can be repeatable. If the goal is to be able to track 'real seconds' - would the RTC be better for this

[Angelo1]

Posted on April 02, 2014 at 22:27 Dear, many thanks for both kind answers. I tested both cases, i can have working the 1 second increment for both cases.