# Changes to CMSIS version V1.20

## 1. Removed CMSIS Middelware packages

CMSIS Middleware is on hold from ARM side until a agreement between all CMSIS partners is found.

## 2. SystemFrequency renamed to SystemCoreClock

The variable name SystemCoreClock is more precise than SystemFrequency because the variable holds the clock value at which the core is running.

## 3. Changed startup concept

The old startup concept (calling SystemInit_ExtMemCtl from startup file and calling SystemInit from main) has the weakness that it does not work for controllers which need a already configuerd clock system to configure the external memory controller.

### Changed startup concept

- SystemInit() is called from startup file before premain.
- SystemInit() configures the clock system and also configures an existing external memory controller.
- SystemInit() must not use global variables.
- SystemCoreClock is initialized with a correct predefined value.
- Additional function void SystemCoreClockUpdate (void) is provided.
  SystemCoreClockUpdate() updates the variable SystemCoreClock and must be called whenever the core clock is changed.
  SystemCoreClockUpdate() evaluates the clock register settings and calculates the current core clock.

## 4. Advanced Debug Functions

ITM communication channel is only capable for OUT direction. To allow also communication for IN direction a simple concept is provided.

- Global variable volatile int ITM_RxBuffer used for IN data.
- Function int ITM_CheckChar (void) checks if a new character is available.
- Function int ITM_ReceiveChar (void) retrieves the new character.

For detailed explanation see file CMSIS debug support.htm.

## 5. Core Register Bit Definitions

Files core_cm3.h and core_cm0.h contain now bit definitions for Core Registers. The name for the defines correspond with the Cortex-M Technical Reference Manual.

e.g. SysTick structure with bit definitions

    /** @addtogroup CMSIS_CM3_SysTick CMSIS CM3 SysTick
      memory mapped structure for SysTick
      @{
     */
    typedef struct
    {
      __IO uint32_t CTRL;                         /*!< Offset: 0x00  SysTick Control and Status Register */
      __IO uint32_t LOAD;                         /*!< Offset: 0x04  SysTick Reload Value Register       */
      __IO uint32_t VAL;                          /*!< Offset: 0x08  SysTick Current Value Register      */
      __I  uint32_t CALIB;                        /*!< Offset: 0x0C  SysTick Calibration Register        */
    } SysTick_Type;

    /* SysTick Control / Status Register Definitions */
    #define SysTick_CTRL_COUNTFLAG_Pos         16                                             /*!< SysTick CTRL: COUNTFLAG Position */
    #define SysTick_CTRL_COUNTFLAG_Msk         (1ul << SysTick_CTRL_COUNTFLAG_Pos)            /*!< SysTick CTRL: COUNTFLAG Mask */

    #define SysTick_CTRL_CLKSOURCE_Pos          2                                             /*!< SysTick CTRL: CLKSOURCE Position */
    #define SysTick_CTRL_CLKSOURCE_Msk         (1ul << SysTick_CTRL_CLKSOURCE_Pos)            /*!< SysTick CTRL: CLKSOURCE Mask */

    #define SysTick_CTRL_TICKINT_Pos            1                                             /*!< SysTick CTRL: TICKINT Position */
    #define SysTick_CTRL_TICKINT_Msk           (1ul << SysTick_CTRL_TICKINT_Pos)              /*!< SysTick CTRL: TICKINT Mask */

    #define SysTick_CTRL_ENABLE_Pos             0                                             /*!< SysTick CTRL: ENABLE Position */
    #define SysTick_CTRL_ENABLE_Msk            (1ul << SysTick_CTRL_ENABLE_Pos)               /*!< SysTick CTRL: ENABLE Mask */

    /* SysTick Reload Register Definitions */
    #define SysTick_LOAD_RELOAD_Pos             0                                             /*!< SysTick LOAD: RELOAD Position */
    #define SysTick_LOAD_RELOAD_Msk            (0xFFFFFFul << SysTick_LOAD_RELOAD_Pos)        /*!< SysTick LOAD: RELOAD Mask */

    /* SysTick Current Register Definitions */
    #define SysTick_VAL_CURRENT_Pos             0                                             /*!< SysTick VAL: CURRENT Position */
    #define SysTick_VAL_CURRENT_Msk            (0xFFFFFFul << SysTick_VAL_CURRENT_Pos)        /*!< SysTick VAL: CURRENT Mask */

    /* SysTick Calibration Register Definitions */
    #define SysTick_CALIB_NOREF_Pos            31                                             /*!< SysTick CALIB: NOREF Position */
    #define SysTick_CALIB_NOREF_Msk            (1ul << SysTick_CALIB_NOREF_Pos)               /*!< SysTick CALIB: NOREF Mask */

    #define SysTick_CALIB_SKEW_Pos             30                                             /*!< SysTick CALIB: SKEW Position */
    #define SysTick_CALIB_SKEW_Msk             (1ul << SysTick_CALIB_SKEW_Pos)                /*!< SysTick CALIB: SKEW Mask */

    #define SysTick_CALIB_TENMS_Pos             0                                             /*!< SysTick CALIB: TENMS Position */
    #define SysTick_CALIB_TENMS_Msk            (0xFFFFFFul << SysTick_VAL_CURRENT_Pos)        /*!< SysTick CALIB: TENMS Mask */
    /*@}*/ /* end of group CMSIS_CM3_SysTick */

## 7. DoxyGen Tags

DoxyGen tags in files core_cm3.[c,h] and core_cm0.[c,h] are reworked to create proper documentation using DoxyGen.

## 8. Folder Structure

The folder structure is changed to differentiate the single support packages.

- CM0
- CM3
  - CoreSupport
  - DeviceSupport
  - Vendor
    - Device
      - Startup
        - Toolchain
        - Toolchain
        - ...
    - Device
    - ...
  - Vendor
  - ...
- Example
  - Toolchain
    - Device
    - Device
    - ...
  - Toolchain
  - ...

- Documentation

## 9. Open Points

Following points need to be clarified and solved:

- Equivalent C and Assembler startup files.

  Is there a need for having C startup files although assembler startup files are very efficient and do not need to be changed?

- Placing of HEAP in external RAM.

  It must be possible to place HEAP in external RAM if the device supports an external memory controller.

- Placing of STACK /HEAP.

  STACK should always be placed at the end of internal RAM.

  If HEAP is placed in internal RAM than it should be placed after RW ZI section.

- Removing core_cm3.c and core_cm0.c.

  On a long term the functions in core_cm3.c and core_cm0.c must be replaced with appropriate compiler intrinsics.

## 10. Limitations

The following limitations are not covered with the current CMSIS version:

- No C startup files for ARM toolchain are provided.
- No C startup files for GNU toolchain are provided.
- No C startup files for IAR toolchain are provided.
- No Tasking projects are provided yet.