Unable to configure Clock using baremetal PLL in stm32 G071RB

Question

i tried to configure clock by writing code in its appropriate registers...
following is the clock configuration function

void SystemClockConfig(void){

#define PLLN 16

//using external clock source

RCC->CR |= RCC_CR_HSEON;

while(!(RCC->CR & RCC_CR_HSERDY));

//enabling power interface

RCC->APBENR1 |= RCC_APBENR1_PWREN;

//configuring voltage regulator to default 01

PWR->CR1 |= (0x1UL << PWR_CR1_VOS_Pos);

PWR->CR1 &= ~(0x2UL << PWR_CR1_VOS_Pos);//

//configure flash prefetch and latency

FLASH->ACR |= (FLASH_ACR_ICEN | FLASH_ACR_PRFTEN | FLASH_ACR_LATENCY_1);

//configuring prescalers for main clock and peripheral clocks

RCC->CFGR |= (RCC_CFGR_HPRE_0 | RCC_CFGR_PPRE_0);

//configure main PLL; PLLM, PLLN, PLLR

RCC->PLLCFGR |= ((PLLN<<8) | (RCC_PLLCFGR_PLLSRC));//

RCC->PLLCFGR &= ~RCC_PLLCFGR_PLLM;

RCC->PLLCFGR |= RCC_PLLCFGR_PLLREN;

RCC->PLLCFGR |= RCC_PLLCFGR_PLLR_0;

//enable PLL

RCC->CR |= RCC_CR_PLLON;

while(!(RCC->CR & RCC_CR_PLLRDY));

//set the clock source

RCC->CFGR |= RCC_CFGR_SW_1;

// while(!(RCC->CFGR & RCC_CFGR_SWS_1));

while(((RCC->CFGR & RCC_CFGR_SWS) != RCC_CFGR_SWS_1));

}

furthermore,

when the Xtal frequency is greyed out as <undefined> in the dialog Options for target - Target tab. so I am unable to set the clock frequency to 64mhz

in the main.c code when I try to include this clock configuration, it fails to make any changes to the code and the simple led blink program fails to execute after flashing

following is my main.c file

#include "stm32g071xx.h"

#include "RCC_CLock_Config.h"

void Timer6Config(void){

//enable Timer 6

RCC->APBENR1 |= (1<<4);

//setting prescaler

//64Mhz/64= 1Mhz -> 1us

TIM6->PSC |= 64-1;//The counter clock frequency CK_CNT is equal to fCK_PSC / (PSC[15:0] + 1).

TIM6->ARR |= 0xffff;

//enabling timer and waiting for flag to set

TIM6->CR1 |= (1<<0);//enable the counter

while(!(TIM6->SR& (1<<0)));

}

void Delay_us(uint16_t time_in_us){

TIM6->CNT = 0;

while(TIM6->CNT<time_in_us);

}

void Delay_ms(uint16_t time_in_ms){

TIM6->CNT=0;

for(uint16_t i=0; i<time_in_ms; i++){

Delay_us(1000);

}

//__attribute__((optimize("-O0")))

void Delay(uint32_t time){

while(time--);

}

void GPIO_Config(void){

RCC->IOPENR |= (1<<2);

GPIOC->MODER &= ~(1<<25);

}

int main(void){

//SystemClockConfig();

Timer6Config();

GPIO_Config();

while(1){

GPIOC->BSRR |= (1<<12);

Delay_ms(500);

GPIOC->BSRR |= (1<<12)<<16;

Delay_ms(500);

}

I am a beginner,

any help would be appreciated.....

STM_Thirty2 · Accepted Answer

Per the User Manual for the Nucleo-G071RB:

Further more you can configure the target to use MCO from STLink:

I modified your register level code to start up the HSI at 64MHz, this code woks and is tested, the rest of you code I did not implement:

void pwr_settings(void){
	//enabling power interface
	RCC->APBENR1 |= RCC_APBENR1_PWREN;
	//configuring voltage regulator to default 01
	PWR->CR1 |= (0x1UL << PWR_CR1_VOS_Pos);
	PWR->CR1 &= ~(0x2UL << PWR_CR1_VOS_Pos);//
	//configure flash prefetch and latency
	FLASH->ACR |= (FLASH_ACR_ICEN | FLASH_ACR_PRFTEN | FLASH_ACR_LATENCY_1);
}

void SystemClockConfig(void){
 #define PLLN 16

 //using internal clock source
 RCC->CR |= RCC_CR_HSION;
 while(!(RCC->CR & RCC_CR_HSIRDY));

 pwr_settings();
 //configure main PLL; PLLM, PLLN, PLLR
 RCC->PLLCFGR &= ~RCC_PLLCFGR_PLLN; // reset PLLN since it is NOT 0 on reset
 RCC->PLLCFGR |= ((8<<RCC_PLLCFGR_PLLN_Pos) | (2<<RCC_PLLCFGR_PLLSRC_Pos));// use HSI , N=8
 RCC->PLLCFGR &= ~RCC_PLLCFGR_PLLM; // M=1
 RCC->PLLCFGR |= RCC_PLLCFGR_PLLR_0; // R=2
 RCC->CR |= RCC_CR_PLLON; //enable PLL
 RCC->PLLCFGR |= RCC_PLLCFGR_PLLREN; // enable PLLR output after PLL is enabled
 while(!(RCC->CR & RCC_CR_PLLRDY)); //wait for PLL to be ready


 //configuring prescalers for main clock and peripheral clocks
 RCC->CFGR &= ~(RCC_CFGR_HPRE); // AHB prescaler to 1
 // set system clock to PLL
 RCC->CFGR |= RCC_CFGR_SW_1; // set system clock to PLL
 // wait for pll to be used as sys clock, check for RCC_CFGR_SWS_1
 while(!(RCC->CFGR & RCC_CFGR_SWS_1));

 // set APB prescaler to 1
 RCC->CFGR &= ~(RCC_CFGR_PPRE); // APB prescaler to 1

 // update cmsis system core clock
 SystemCoreClockUpdate(); // CMSIS defdined function to update SystemCoreClock variable

}

waclawek.jan · Answer

I assume you see blinking with SystemClockConfig() commented out, and that you are aware of that 8x faster blinking may be too fast to see by eye.

I don't see anything fatal in your code.

Can you single-step the SystemClockConfig() code and observe the registers' content? Or at least, try variants with lighting up the LED at various points of SystemClockConfig() and see how far does it get.

JW

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