Systick delay problem in KEIL STM32F407 descovery

[yefj]

Hello,I have tried to create a systick delay using systick interrupt as shown in the code bellow.
But i cant see what is the link between the core frequency and the actual delay of the sistick interrupt.
How can i link the core frequency to the actual delay?


HAL MANUAL STM32FG14
https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.DM00105879.pdf

STM32F407 RM
https://www.st.com/resource/en/refe...-arm-based-32-bit-mcus-stmicroelectronics.pdf

#include "stm32f407xx.h"

volatile uint16_t delay_count=0;
void SysTick_Handler(void)//called every 1ms
{
    if (delay_count>0)
    {
         delay_count--;
    }
}
void delay_ms(uint16_t delay_temp)
{
    delay_count=delay_temp;
    while(delay_count){}
}
int main()
{
   
   
    RCC->AHB1ENR|=(1uL<<3); //set thirdbit
    //GPIOD->MODER&=~(1uL<<31);//reset 0 on 31 01 to gpio_moder 31,30 bits in register
    //GPIOD->MODER|=(1uL<<30);//set 1 on 30 output mode for pin 15 port D
    GPIOD->MODER=0x55000000;
   
    SysTick_Config(SystemCoreClock/1000);//1 ms interrupt
   
    GPIOD->OTYPER=0; //all register is push pull
    GPIOD->OSPEEDR=0;//speed low
     //GPIOD->ODR|=(1<<15); //Sets pin 15

    while(1)
       
    {
         GPIOD->BSRR=(1uL<<15);
             delay_ms(500);
     GPIOD->BSRR=(1uL<<(15+16));      
       delay_ms(500);

    }
}