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-Core(M) Device Peripheral Access Layer Source File for
 *           Device <Device>
 * @version  V1.0.0
 * @date     20. January 2021
 *****************************************************************************/
/*
 * Copyright (c) 2009-2021 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"

/* ToDo: Include partition header file if TZ is used */
#if defined (__ARM_FEATURE_CMSE) &&  (__ARM_FEATURE_CMSE == 3U)
  #include "partition_<Device>.h"
#endif


/*---------------------------------------------------------------------------
  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)


/*---------------------------------------------------------------------------
  Exception / Interrupt Vector table
 *---------------------------------------------------------------------------*/
extern const VECTOR_TABLE_Type __VECTOR_TABLE[496];


/*---------------------------------------------------------------------------
  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)*/


/*---------------------------------------------------------------------------
  System Core Clock function
 *---------------------------------------------------------------------------*/
void SystemCoreClockUpdate (void)
{
/* 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;
}


/*---------------------------------------------------------------------------
  System initialization function
 *---------------------------------------------------------------------------*/
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. */

/* ToDo: Initialize VTOR if available */
#if defined (__VTOR_PRESENT) && (__VTOR_PRESENT == 1U)
  SCB->VTOR = (uint32_t)(&__VECTOR_TABLE[0]);
#endif

/* ToDo: Enable co-processor if it is used */
#if (defined (__FPU_USED) && (__FPU_USED == 1U)) || \
    (defined (__ARM_FEATURE_MVE) && (__ARM_FEATURE_MVE > 0U))
  SCB->CPACR |= ((3U << 10U*2U) |           /* enable CP10 Full Access */
                 (3U << 11U*2U)  );         /* enable CP11 Full Access */
#endif

/* ToDo: Initialize SAU if TZ is used */
#if defined (__ARM_FEATURE_CMSE) && (__ARM_FEATURE_CMSE == 3U)
  TZ_SAU_Setup();
#endif

  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-Core(M) Device Peripheral Access Layer Header File for
 *           Device <Device>
 * @version  V1.0.0
 * @date     20. January 2021
 *****************************************************************************/
/*
 * Copyright (c) 2009-2021 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

/**
  \brief Exception / Interrupt Handler Function Prototype
*/
typedef void(*VECTOR_TABLE_Type)(void);

/**
  \brief System Clock Frequency (Core Clock)
*/
extern uint32_t SystemCoreClock;

/**
  \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 */