Question

If you want to have a 4 second delay and you have configured SysTick to create 0.2 second delay, how do you get a 4 second delay in software?

Answer in C code.

Answer 1

• SysTick is a timer which generates an interrupt after the configured time delay and the controls goes to the SysTick_Handler function.
• As per the question, the SysTick is configured for 0.2 seconds, after every 0.2 seconds the control of the CPU(Microcontroller) goes to the SysTick_Handler function.
• There are multiple ways to generate 4 seconds delay using 0.2 second configured SysTick timer. The common approach is to use a global variable tickCount and incrementing it for each 0.2 second(when controls goes to SysTick_Handler).
• For generating 4 second delay, the tickCount variable can be monitored for its value. Whenever the tickCount value is 20 (4 seconds / 0.2 second = 20) or multiple of 20, then the 4 second delay is generated.
• From the code, it is understood in better way.
• Please note that, based on the different microcontroller, you may need to setup 0.2 second SysTick differently.
• The program is for understanding purpose.

C Code:

#include "LPC17xx.h"
  
volatile uint32_t tickCount = 0; /* Variable to count 0.2 seconds ticks */
  
/* Interrupt Hanlder of SysTick for 0.2 seconds */
/* The control of the program comes to this function after each 0.2 second */
void SysTick_Handler(void) {   
tickCount++; /* See startup file startup_LPC17xx.s for SysTick vector */
}

void dealy_4_Second(void){
/* Waiting for the 20 tickCount, for 4 seconds and control will be inside while loop */
while(tickCount%20);
}

int main (void) {
/* Configuring SysTick for 0.2 = 200 milliseconds */
uint32_t sysConfigReturn;
sysConfigReturn = SysTick_Config(200*SystemCoreClock / 1000);
/* Code before delay */
delay_4_Second();
/* Code after delay */
  
while(1); // continuous loop
return 0;
}