Thread: Defining a number that will be used throughout an entire program.

Hi

I am going wrong somewhere with something that i feel should be quite simple.

I have a header file called MCU_Config, In there SYS_FREQ is defined.

Code:

#ifndef _MCU_CONFIG_H        
#define _MCU_CONFIG_H


#define SYS_FREQ 80000000

In another header file i want to use the definition SYS_FREQ but i get an error telling me that i have an undeclared first use for SYS_FREQ

Code:

#ifndef _DELAY_H        
#define _DELAY_H    


#include <xc.h>


//#define SYS_FREQ 80000000                  // RUNNING AT 80MHz


/////////////////////////
// FUNCTION PROTOTYPES //
/////////////////////////
void Delay_mS(int msec);                   //Initialise UART1 Communication


#endif

This is the .c file where SYS_FREQ is called.

Code:

#include "Delay.h"




void Delay_mS(int msec)
{
    unsigned int tWait;
    
    tWait=(SYS_FREQ / 2000)*msec;       // Calculate clock cycles required
    _CP0_SET_COUNT(0);                  // Set Core Timer count to 0
    while (_CP0_GET_COUNT()<tWait);     // Wait until Core Timer count reaches the number we calculated earlier 
}

If i uncomment SYS_FREQ in the header file then the program works as expected.

If i include MCU_Config.h then i get multiple errors about multiple definitions.

SYS_FREQ is used in a couple of places in my program. On 3 different UARTS Delay and probably will be used elsewhere as it develops.

I dont want to be changing all these header files should i ever change the frequency.
So is it possible to have this defined in one place and allow all files to use it?


This is my main()

Code:

// Section: Included Files 
#include "MCU_Config.h"
#include "UART1_Comms.h"
#include "VT100.h"
#include "Delay.h"


#include <xc.h>
#include <stdio.h>
#include <stdbool.h>
#include <proc/p32mx575f256l.h>

#define LED1 LATBbits.LATB7

void main()
{   

    // Main loop    while(1) 
    {
        LED1 = 0;
        Delay_mS(1000);
        LED1 = 1; 
        Delay_mS(1000);        
    }
    
}