/**
  ******************************************************************************
  * @file    CortexM/Mode_Privilege/main.c 
  * @author  MCD Application Team
  * @version V1.3.0
  * @date    13-November-2013
  * @brief   Main program body
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; COPYRIGHT 2013 STMicroelectronics</center></h2>
  *
  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
  *
  *        http://www.st.com/software_license_agreement_liberty_v2
  *
  * 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.
  *
  ******************************************************************************
  */

/* Includes ------------------------------------------------------------------*/
#include "stm32f4xx.h"

/** @addtogroup STM32F4xx_StdPeriph_Examples
  * @{
  */

/** @addtogroup CortexM_Mode_Privilege
  * @{
  */ 

/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
#define SP_PROCESS_SIZE             0x200  /* Process stack size */
#define SP_PROCESS                  0x02   /* Process stack */
#define SP_MAIN                     0x00   /* Main stack */
#define THREAD_MODE_PRIVILEGED      0x00   /* Thread mode has privileged access */
#define THREAD_MODE_UNPRIVILEGED    0x01   /* Thread mode has unprivileged access */
    
 /* Private function prototypes -----------------------------------------------*/
static __INLINE  void __SVC(void); 
 
/* Private macro -------------------------------------------------------------*/
#if defined ( __CC_ARM   )
 __ASM void __SVC(void) 
 { 
   SVC 0x01 
   BX R14
 }
#elif defined ( __ICCARM__ )
 static __INLINE  void __SVC()                     { __ASM ("svc 0x01");}
#elif defined   (  __GNUC__  )
 static __INLINE void __SVC()                      { __ASM volatile ("svc 0x01");}
 #elif defined ( __TASKING__ )
 static __INLINE  void __SVC()                     { __ASM ("svc 0x01");}
#endif

/* Private variables ---------------------------------------------------------*/
__IO uint8_t PSPMemAlloc[SP_PROCESS_SIZE];
__IO uint32_t Index = 0, PSPValue = 0, CurrentStack = 0, ThreadMode = 0;

/* Private functions ---------------------------------------------------------*/

/**
  * @brief  Main program
  * @param  None
  * @retval None
  */
int main(void)
{
  /*!< At this stage the microcontroller clock setting is already configured, 
       this is done through SystemInit() function which is called from startup
       files (startup_stm32f40_41xxx.s/startup_stm32f427_437xx.s/startup_stm32f429_439xx.s)
       before to branch to application main. 
       To reconfigure the default setting of SystemInit() function, refer to
       system_stm32f4xx.c file
     */     
       
/* Switch Thread mode Stack from Main to Process -----------------------------*/
  /* Initialize memory reserved for Process Stack */
  for(Index = 0; Index < SP_PROCESS_SIZE; Index++)
  {
    PSPMemAlloc[Index] = 0x00;
  }

  /* Set Process stack value */ 
  __set_PSP((uint32_t)PSPMemAlloc + SP_PROCESS_SIZE);
  
  /* Select Process Stack as Thread mode Stack */
  __set_CONTROL(SP_PROCESS);

  /* Get the Thread mode stack used */
  if((__get_CONTROL() & 0x02) == SP_MAIN)
  {
    /* Main stack is used as the current stack */
    CurrentStack = SP_MAIN;
  }
  else
  {
    /* Process stack is used as the current stack */
    CurrentStack = SP_PROCESS;

    /* Get process stack pointer value */
    PSPValue = __get_PSP();	
  }
  
/* Switch Thread mode from privileged to unprivileged ------------------------*/
  /* Thread mode has unprivileged access */
  __set_CONTROL(THREAD_MODE_UNPRIVILEGED | SP_PROCESS);

  /* Unprivileged access mainly affect ability to:
      - Use or not use certain instructions such as MSR fields
      - Access System Control Space (SCS) registers such as NVIC and SysTick */

  /* Check Thread mode privilege status */
  if((__get_CONTROL() & 0x01) == THREAD_MODE_PRIVILEGED)
  {
    /* Thread mode has privileged access  */
    ThreadMode = THREAD_MODE_PRIVILEGED;
  }
  else
  {
    /* Thread mode has unprivileged access*/
    ThreadMode = THREAD_MODE_UNPRIVILEGED;
  }

/* Switch back Thread mode from unprivileged to privileged -------------------*/  
  /* Try to switch back Thread mode to privileged (Not possible, this can be
     done only in Handler mode) */
  __set_CONTROL(THREAD_MODE_PRIVILEGED | SP_PROCESS);

  /* Generate a system call exception, and in the ISR switch back Thread mode
    to privileged */
  __SVC();

  /* Check Thread mode privilege status */
  if((__get_CONTROL() & 0x01) == THREAD_MODE_PRIVILEGED)
  {
    /* Thread mode has privileged access  */
    ThreadMode = THREAD_MODE_PRIVILEGED;
  }
  else
  {
    /* Thread mode has unprivileged access*/
    ThreadMode = THREAD_MODE_UNPRIVILEGED;
  }

  while (1)
  {
  }
}

#ifdef  USE_FULL_ASSERT

/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t* file, uint32_t line)
{ 
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */

  /* Infinite loop */
  while (1)
  {
  }
}
#endif

/**
  * @}
  */ 

/**
  * @}
  */ 

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/
