CMSIS-Core (Cortex-M): Using CMSIS in Embedded Applications

| CMSIS-Core (Cortex-M) Version 5.0.2 CMSIS-Core support for Cortex-M processor-based devices

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- Usage and Description
- Reference

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Using CMSIS in Embedded Applications

To use the CMSIS-Core (Cortex-M) the following files are added to the embedded application:

- Startup File startup_<device>.s with reset handler and exception vectors.
- System Configuration Files system_<device>.c and system_<device>.h with general device configuration (i.e. for clock and BUS setup).
- Device Header File <device.h> gives access to processor core and all peripherals.

Note
  The files Startup File startup_<device>.s and System Configuration Files system_<device>.c and system_<device>.h may require application specific adaptations and therefore should be copied into the application project folder prior configuration. The Device Header File <device.h> is included in all source files that need device access and can be stored on a central include folder that is generic for all projects.

The Startup File startup_<device>.s is executed after reset and calls SystemInit. After the system initialization control is transferred to the C/C++ run-time library which performs initialization and calls the main function in the user code. In addition the Startup File startup_<device>.s contains all exception and interrupt vectors and implements a default function for every interrupt. It may also contain stack and heap configurations for the user application.

The System Configuration Files system_<device>.c and system_<device>.h performs the setup for the processor clock. The variable SystemCoreClock indicates the CPU clock speed. System and Clock Configuration describes the minimum feature set. In addition the file may contain functions for the memory BUS setup and clock re-configuration.

The Device Header File <device.h> is the central include file that the application programmer is using in the C source code. It provides the following features:

- Peripheral Access provides a standardized register layout for all peripherals. Optionally functions for device-specific peripherals may be available.
- Interrupts and Exceptions (NVIC) can be accessed with standardized symbols and functions for the Nested Interrupt Vector Controller (NVIC) are provided.
- Intrinsic Functions for CPU Instructions allow to access special instructions, for example for activating sleep mode or the NOP instruction.
- Intrinsic Functions for SIMD Instructions [only Cortex-M4 and Cortex-M7] provide access to the DSP-oriented instructions.
- Systick Timer (SYSTICK) function to configure and start a periodic timer interrupt.
- Debug Access are functions that allow printf-style I/O via the CoreSight Debug Unit and ITM communication.

CMSIS-Core (Cortex-M) User Files

The CMSIS-Core (Cortex-M) are device specific. In addition, the Startup File startup_<device>.s is also compiler vendor specific. The various compiler vendor tool chains may provide folders that contain the CMSIS files for each supported device.

For example, the following files are provided in MDK-ARM to support the STM32F10x Connectivity Line device variants:

File | Description
--- | ---
".\ARM\Startup\ST\STM32F10x\startup_stm32f10x_cl.s" | Startup File startup_<device>.s for the STM32F10x Connectivity Line device variants.
".\ARM\Startup\ST\STM32F10x\system_stmf10x.c" | System Configuration Files system_<device>.c and system_<device>.h for the STM32F10x device families.
".\ARM\INC\ST\STM32F10x\stm32f10x.h" | Device Header File <device.h> for the STM32F10x device families.
".\ARM\INC\ST\STM32F10x\system_stm32f10x.h" | system_Device.h Template File for the STM32F10x device families.

Note
  The silicon vendors create these device-specific CMSIS-Core (Cortex-M) files based on CMSIS-Core Device Templates provide by ARM.

Thereafter, the functions described under Reference can be used in the application.

Examples

- Basic CMSIS Example is a simple example that shows the usage of the CMSIS layer.
- Using Interrupt Vector Remap shows how to remap the interrupt vector table.
- Using CMSIS with generic ARM Processors explains how to use CMSIS-Core (Cortex-M) for ARM processors.