The System Configuration Files system_<device>.c and system_<device>.h provides as a minimum the functions described under System and Clock Configuration. These functions are device specific and need adaptations. In addition, the file might have configuration settings for the device such as XTAL frequency or PLL prescaler settings.

For devices with external memory BUS the system_<device>.c also configures the BUS system.

The silicon vendor might expose other functions (i.e. for power configuration) in the system_<device>.c file. In case of additional features the function prototypes need to be added to the system_<device>.h header file.

system_Device.c Template File

The system_Device.c Template File for the Cortex-M3 is shown below.

/**************************************************************************//**
 * @file     system_<Device>.c
 * @brief    CMSIS Cortex-M# Device Peripheral Access Layer Source File for
 *           Device <Device>
 * @version  V3.01
 * @date     06. March 2012
 *
 * @note
 * Copyright (C) 2010-2012 ARM Limited. All rights reserved.
 *
 * @par
 * ARM Limited (ARM) is supplying this software for use with Cortex-M 
 * processor based microcontrollers.  This file can be freely distributed 
 * within development tools that are supporting such ARM based processors. 
 *
 * @par
 * THIS SOFTWARE IS PROVIDED "AS IS".  NO WARRANTIES, WHETHER EXPRESS, IMPLIED
 * OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE.
 * ARM SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL, OR
 * CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
 *
 ******************************************************************************/


#include <stdint.h>
#include "<Device>.h"


/*----------------------------------------------------------------------------
  DEFINES
 *----------------------------------------------------------------------------*/
    
/*----------------------------------------------------------------------------
  Define clocks
 *----------------------------------------------------------------------------*/
/* ToDo: add here your necessary defines for device initialization     
         following is an example for different system frequencies             */
#define __HSI             ( 6000000UL)
#define __XTAL            (12000000UL)    /* Oscillator frequency             */
#define __SYS_OSC_CLK     (    ___HSI)    /* Main oscillator frequency        */

#define __SYSTEM_CLOCK    (4*__XTAL)


/*----------------------------------------------------------------------------
  Clock Variable definitions
 *----------------------------------------------------------------------------*/
/* ToDo: initialize SystemCoreClock with the system core clock frequency value
         achieved after system intitialization.
         This means system core clock frequency after call to SystemInit()    */
uint32_t SystemCoreClock = __SYSTEM_CLOCK;  /*!< System Clock Frequency (Core Clock)*/


/*----------------------------------------------------------------------------
  Clock functions
 *----------------------------------------------------------------------------*/
void SystemCoreClockUpdate (void)            /* Get Core Clock Frequency      */
{
/* ToDo: add code to calculate the system frequency based upon the current
         register settings.
         This function can be used to retrieve the system core clock frequeny
         after user changed register sittings.                                */
  SystemCoreClock = __SYSTEM_CLOCK;
}

/**
 * Initialize the system
 *
 * @param  none
 * @return none
 *
 * @brief  Setup the microcontroller system.
 *         Initialize the System.
 */
void SystemInit (void)
{
/* ToDo: add code to initialize the system
         do not use global variables because this function is called before
         reaching pre-main. RW section maybe overwritten afterwards.          */
  SystemCoreClock = __SYSTEM_CLOCK;
}

system_Device.h Template File

The system_<device>.h header file contains prototypes to access the public functions in the system_<device>.c file. The system_Device.h Template File is shown below.

/**************************************************************************//**
 * @file     system_<Device>.h
 * @brief    CMSIS Cortex-M# Device Peripheral Access Layer Header File for
 *           Device <Device>
 * @version  V3.01
 * @date     06. March 2012
 *
 * @note
 * Copyright (C) 2010-2012 ARM Limited. All rights reserved.
 *
 * @par
 * ARM Limited (ARM) is supplying this software for use with Cortex-M 
 * processor based microcontrollers.  This file can be freely distributed 
 * within development tools that are supporting such ARM based processors. 
 *
 * @par
 * THIS SOFTWARE IS PROVIDED "AS IS".  NO WARRANTIES, WHETHER EXPRESS, IMPLIED
 * OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE.
 * ARM SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR SPECIAL, INCIDENTAL, OR
 * CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
 *
 ******************************************************************************/


#ifndef SYSTEM_<Device>_H   /* ToDo: replace '<Device>' with your device name */
#define SYSTEM_<Device>_H

#ifdef __cplusplus
extern "C" {
#endif

#include <stdint.h>

extern uint32_t SystemCoreClock;     /*!< System Clock Frequency (Core Clock)  */


/**
 * Initialize the system
 *
 * @param  none
 * @return none
 *
 * @brief  Setup the microcontroller system.
 *         Initialize the System and update the SystemCoreClock variable.
 */
extern void SystemInit (void);

/**
 * Update SystemCoreClock variable
 *
 * @param  none
 * @return none
 *
 * @brief  Updates the SystemCoreClock with current core Clock 
 *         retrieved from cpu registers.
 */
extern void SystemCoreClockUpdate (void);

#ifdef __cplusplus
}
#endif

#endif /* SYSTEM_<Device>_H */