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  V5.00
 * @date     10. January 2018
 ******************************************************************************/
/*
 * Copyright (c) 2009-2018 Arm Limited. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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


/*----------------------------------------------------------------------------
  Define clocks
 *----------------------------------------------------------------------------*/
/* ToDo: add here your necessary defines for device initialization
         following is an example for different system frequencies */
#define XTAL            (12000000U)       /* Oscillator frequency             */

#define SYSTEM_CLOCK    (5 * XTAL)


/*----------------------------------------------------------------------------
  System Core Clock Variable
 *----------------------------------------------------------------------------*/
/* 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;
}

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  V5.00
 * @date     10. January 2018
 ******************************************************************************/
/*
 * Copyright (c) 2009-2018 Arm Limited. All rights reserved.
 *
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#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)  */


/**
  \brief Setup the microcontroller system.

   Initialize the System and update the SystemCoreClock variable.
 */
extern void SystemInit (void);


/**
  \brief  Update SystemCoreClock variable.

   Updates the SystemCoreClock with current core Clock retrieved from cpu registers.
 */
extern void SystemCoreClockUpdate (void);


#ifdef __cplusplus
}
#endif

#endif /* SYSTEM_<Device>_H */