After Restart, Delay time decrease

[piyushsurani]

code running ok with 1 second delay in stm32f103c8t6 bluepill board. but, after power off when i do power on, delay is 0.56 second. I am using 72 MHz timer2 clock.

#include "stm32f1xx.h"

void TIM2_Init_ms(uint16_t delay_ms);

void clock_setup();

int main(void)

{

clock_setup();

    TIM2_Init_ms(1000);

while(1)

{}

}

 void TIM2_IRQHandler(void)

 {

     if (TIM2->SR & TIM_SR_UIF)

            {

                TIM2->SR &= ~TIM_SR_UIF;   // Clear update flag

                GPIOC->ODR ^= GPIO_ODR_ODR13;     // set and reset Bit 13 of ODR //togglr bit and so LED

            }

 }

void TIM2_Init_ms(uint16_t delay_ms)

{

    RCC->APB1ENR |= RCC_APB1ENR_TIM2EN;

    TIM2->PSC = 7199;              // 0.1 ms tick

    TIM2->ARR = (delay_ms * 10) - 1;

    TIM2->EGR |= TIM_EGR_UG;           // Load PSC + ARR

    TIM2->CNT = 0;                     // RESET counter (IMPORTANT)

    TIM2->DIER |= TIM_DIER_UIE;

    NVIC_EnableIRQ(TIM2_IRQn);

    TIM2->CR1 |= TIM_CR1_CEN;

}

void clock_setup()

{

//Clock Setting

    RCC->CR |= RCC_CR_HSEON; //bit 16 (High Speed External Clock ) ON of Clock Control Register

    while (!(RCC->CR & RCC_CR_HSERDY)); // wait till external oscillator stable

    //Flash Access

    FLASH->ACR |= FLASH_ACR_LATENCY_2; // 2 wait cycle of CPU required for 72MHZ frequency to access flash

    FLASH->ACR |= FLASH_ACR_PRFTBE; //to prefetch data from flash when cpu access other data

    // PLL Setup

    RCC->CFGR |= RCC_CFGR_PLLSRC;         // PLL source from external oscillator

    RCC->CFGR |= RCC_CFGR_PLLMULL9;       // PLL Multiply with 9 to get 72MHZ Clock

    // APB1 Setup

    RCC->CFGR |= RCC_CFGR_PPRE1_DIV2; //set apb1 prescaler 2 to get max 36 MHZ

    // Enable PLL

    RCC->CR |= RCC_CR_PLLON; //start PLL

    while (!(RCC->CR & RCC_CR_PLLRDY)); //wait till PLL Frequency stable

    RCC->CFGR |= RCC_CFGR_SW_PLL; //PLL configure as system clock

    while ((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_PLL); //wait till system clock = PLL

    RCC->APB2ENR |= RCC_APB2ENR_IOPCEN;//GPIO PORTC clock enable

    GPIOC->CRH &= ~(GPIO_CRH_MODE13 | GPIO_CRH_CNF13); // clear port 13 old setting

    GPIOC->CRH |=  GPIO_CRH_MODE13_1;     // Port13 2Mz Push pull output set

}

[TDK]

How do you measure the delay? Your code has no effect on anything. Ahh, it toggles a pin. 72 MHz * .56 = 40 MHz. Not the default speed, so who knows.

Most likely this is a counterfeit chip so any documents from ST which says how it operates are not relevant.

[piyushsurani]

It is countetfeit chip. But, problem was in setup of PLL Clock. We need to reset old PLL multiplication factor before assign it new. 

[mƎALLEm]

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@piyushsurani wrote:

It is countetfeit chip. 

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For a counterfeit chips you need to ask their manufacturer(s).