diagram.json

#include "gpio.h"
#include "stm32c0xx.h"
#include "system.h"



void setup() {

  pin_mode(PinA5, OutputPushPull);
//  if ((RCC->CFGR >> RCC_CFGR_SWS_Pos) & 7 == 0)
//    pin_set(PinA5);
//  printf("SWS %d\n", (RCC->CFGR >> RCC_CFGR_SWS_Pos) & 7);

  //SystemCoreClockUpdate();
	//SysTick_Config(SystemCoreClock / 1000);
}

void loop() {
  if (system_ms() % 1000 < 500)
    pin_set(PinA5);
  else
    pin_reset(PinA5);
  //printf("%d\n", ms);
}

//#include "stdio.h"
//#include "float.h"

/*
void RCC_Config ()
{
  RCC->IOPENR|= (1UL << 1); // Enable the GPIOB peripheral
  RCC->IOPENR|= (1UL << 0); // Enable the GPIOA peripheral
 
  RCC->CR&=~(1<<8); //HSI OFF
  RCC->CR|=(1<<16); //HSE ON
  RCC->CR|=1<<19;            //  CSS ON (SECURITY) optional
  RCC->CR=0x00090000; 
  while (!(RCC->CR & (1<<17)));//wait HSE flag active. while(1) in loop, but while(0) out loop. When HSE is on(1 and 1=1 and !1-0)  then while(0) out loop
	

   RCC->CFGR&=~(1<<2); //  System clock switch source HSE 
   RCC->CFGR&=~(1<<1); //  System clock switch source HSE 
   RCC->CFGR|=(1<<0); //  System clock switch source HSE

   RCC->CFGR|=(1<<24); //  Microcontroller clock output clock selecto
   RCC->CFGR|=(2<<8); //AHB prescaler 2

   RCC->AHBENR|=(1<<12);//CRC clock enable
   RCC->AHBENR|=(1<<8);//CRC clock enable
   RCC->APBENR2|=1<<20;//APB2 bus enable for ADC 



}

void GPIO_Config () {

GPIOA->MODER|=3<<4;
} 



////////////////////////////////////


void ADC_Config ()   {

ADC1->CR&=~(1<<0); //ADC is OFF
 while(ADC1->ISR&(1<<0))
 
  
  ADC1->CFGR1|=1<<13;
  ADC1->CFGR1|2<<3;
  ADC1->CHSELR|=1<<2;
  ADC1->CR|=1<<0;
  while(!(ADC1->ISR&(1<<0)));

 }

float voltage;
int integer_voltage;
int fractional_voltage;

int fraction_extractor (int integer_voltage, float voltage ) {
fractional_voltage=1000*(voltage-integer_voltage);
return fractional_voltage;
}


 int main () {
 RCC_Config ();
GPIO_Config ();
 ADC_Config ();


while(1) {
    ADC1->CR |= 1 << 2; // Start the conversion
   
    int analog_value = ADC1->DR ;  // Reading Data Register
    
    voltage=(3.3/4095)*analog_value;
    
    fractional_voltage=fraction_extractor (integer_voltage,  voltage );
    integer_voltage=voltage;
    //printf("Analog voltage: %d.%d V\n", integer_voltage, fractional_voltage);
  }}

*/


main.c

#ifndef _system_h
#define _system_h
#include <stdint.h>

#ifdef __cplusplus
extern "C" {
#endif
uint32_t system_ms();
void setup();
void loop();
#ifdef __cplusplus
}
#endif
#endif


system.h

#include <stm32c0xx.h>
#include "system.h"
#include <stdint.h>

static volatile uint32_t _system_ticks;

void systick_handler() {
	_system_ticks++;
}

uint32_t system_ms() {
  return _system_ticks;
}

void system_init(void) {
	/*FLASH->ACR &=~FLASH_ACR_LATENCY_0; // latency 2 wait states
	FLASH->ACR |= FLASH_ACR_LATENCY_1;
	RCC->CR |= RCC_CR_HSEON; // enable hse
	while (!(RCC->CR & RCC_CR_HSERDY));
	RCC->CFGR |= RCC_CFGR_PLLSRC // HSE as PLL input
		| RCC_CFGR_PPRE1_DIV2 // APB1 prescale 2 (<36MHz)
		| RCC_CFGR_PLLMULL9; // clk = 8 * 9 = 72Mhz
	RCC->CR |= RCC_CR_PLLON;
	while (!(RCC->CR & RCC_CR_PLLRDY));
	RCC->CFGR |= RCC_CFGR_SW_PLL; // PLL as system clock source*/

	FLASH->ACR = (FLASH->ACR & FLASH_ACR_LATENCY_Msk) | FLASH_ACR_LATENCY_0; // 1 wait state
  RCC->CR |= RCC_CR_HSEON;
  while (!(RCC->CR & RCC_CR_HSERDY));
  RCC->CFGR = (RCC->CFGR & ~RCC_CFGR_SW_Msk) | 1 << RCC_CFGR_SW_Pos;

	SystemCoreClockUpdate();
	SysTick_Config(SystemCoreClock / 1000);
	__enable_irq();
}

int main() {
	system_init();
	setup();
	while (1)
		loop();
}
