/**
******************************************************************************
* @file    system_stm32f0xx.c
* @author  MCD Application Team
* @version V1.0.1
* @date    14-July-2014
* @brief   CMSIS Cortex-M0 Device Peripheral Access Layer System Source File.
*          This file contains the system clock configuration for STM32F0xx devices,
*          and is generated by the clock configuration tool
*          STM32f0xx_Clock_Configuration_V1.0.1.xls
*
* 1.  This file provides two functions and one global variable to be called from
*     user application:
*      - SystemInit(): Setups the system clock (System clock source, PLL Multiplier
*                      and Divider factors, AHB/APBx prescalers and Flash settings),
*                      depending on the configuration made in the clock xls tool.
*                      This function is called at startup just after reset and
*                      before branch to main program. This call is made inside
*                      the "startup_stm32f0xx.s" file.
*
*      - SystemCoreClock variable: Contains the core clock (HCLK), it can be used
*                                  by the user application to setup the SysTick
*                                  timer or configure other parameters.
*
*      - SystemCoreClockUpdate(): Updates the variable SystemCoreClock and must
*                                 be called whenever the core clock is changed
*                                 during program execution.
*
* 2. After each device reset the HSI (8 MHz Range) is used as system clock source.
*    Then SystemInit() function is called, in "startup_stm32f0xx.s" file, to
*    configure the system clock before to branch to main program.
*
* 3. If the system clock source selected by user fails to startup, the SystemInit()
*    function will do nothing and HSI still used as system clock source. User can
*    add some code to deal with this issue inside the SetSysClock() function.
*
* 4. The default value of HSE crystal is set to 8MHz, refer to "HSE_VALUE" define
*    in "stm32f0xx.h" file. When HSE is used as system clock source, directly or
*    through PLL, and you are using different crystal you have to adapt the HSE
*    value to your own configuration.
*
* 5. This file configures the system clock as follows:
*=============================================================================
*=============================================================================
*        System Clock source                    | PLL(HSI)
*-----------------------------------------------------------------------------
*        SYSCLK(Hz)                             | 48000000
*-----------------------------------------------------------------------------
*        HCLK(Hz)                               | 48000000
*-----------------------------------------------------------------------------
*        AHB Prescaler                          | 1
*-----------------------------------------------------------------------------
*        APB Prescaler                          | 1
*-----------------------------------------------------------------------------
*        HSE Frequency(Hz)                      | NA
*----------------------------------------------------------------------------
*        PLLMUL                                 | 12
*-----------------------------------------------------------------------------
*        PREDIV                                 | 2
*-----------------------------------------------------------------------------
*        Flash Latency(WS)                      | 1
*-----------------------------------------------------------------------------
*        Prefetch Buffer                        | ON
*-----------------------------------------------------------------------------
******************************************************************************
* @attention
*
* 

*
* 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.
*
******************************************************************************
*/
/** @addtogroup CMSIS
* @{
*/
/** @addtogroup stm32f0xx_system
* @{
*/
/** @addtogroup STM32F0xx_System_Private_Includes
* @{
*/
#include "stm32f0xx.h"
/**
* @}
*/
/** @addtogroup STM32F0xx_System_Private_TypesDefinitions
* @{
*/
/**
* @}
*/
/** @addtogroup STM32F0xx_System_Private_Defines
* @{
*/
/**
* @}
*/
/** @addtogroup STM32F0xx_System_Private_Macros
* @{
*/
/**
* @}
*/
/** @addtogroup STM32F0xx_System_Private_Variables
* @{
*/
uint32_t SystemCoreClock    = 48000000;
__I uint8_t AHBPrescTable[16] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 6, 7, 8, 9};
/**
* @}
*/
/** @addtogroup STM32F0xx_System_Private_FunctionPrototypes
* @{
*/
static void SetSysClock(void);
/**
* @}
*/
/** @addtogroup STM32F0xx_System_Private_Functions
* @{
*/
/**
* @brief  Setup the microcontroller system.
*         Initialize the Embedded Flash Interface, the PLL and update the
*         SystemCoreClock variable.
* @param  None
* @retval None
*/
void SystemInit (void)
{
/* Set HSION bit */
RCC->CR |= (uint32_t)0x00000001;
/* Reset SW[1:0], HPRE[3:0], PPRE[2:0], ADCPRE and MCOSEL[2:0] bits */
RCC->CFGR &= (uint32_t)0xF8FFB80C;
/* Reset HSEON, CSSON and PLLON bits */
RCC->CR &= (uint32_t)0xFEF6FFFF;
/* Reset HSEBYP bit */
RCC->CR &= (uint32_t)0xFFFBFFFF;
/* Reset PLLSRC, PLLXTPRE and PLLMUL[3:0] bits */
RCC->CFGR &= (uint32_t)0xFFC0FFFF;
/* Reset PREDIV1[3:0] bits */
RCC->CFGR2 &= (uint32_t)0xFFFFFFF0;
/* Reset USARTSW[1:0], I2CSW, CECSW and ADCSW bits */
RCC->CFGR3 &= (uint32_t)0xFFFFFEAC;
/* Reset HSI14 bit */
RCC->CR2 &= (uint32_t)0xFFFFFFFE;
/* Disable all interrupts */
RCC->CIR = 0x00000000;
/* Configure the System clock frequency, AHB/APBx prescalers and Flash settings */
SetSysClock();
}
/**
* @brief  Update SystemCoreClock according to Clock Register Values
*         The SystemCoreClock variable contains the core clock (HCLK), it can
*         be used by the user application to setup the SysTick timer or configure
*         other parameters.
*
* @note   Each time the core clock (HCLK) changes, this function must be called
*         to update SystemCoreClock variable value. Otherwise, any configuration
*         based on this variable will be incorrect.
*
* @note   - The system frequency computed by this function is not the real
*           frequency in the chip. It is calculated based on the predefined
*           constant and the selected clock source:
*
*           - If SYSCLK source is HSI, SystemCoreClock will contain the HSI_VALUE(*)
*
*           - If SYSCLK source is HSE, SystemCoreClock will contain the HSE_VALUE(**)
*
*           - If SYSCLK source is PLL, SystemCoreClock will contain the HSE_VALUE(**)
*             or HSI_VALUE(*) multiplied/divided by the PLL factors.
*
*         (*) HSI_VALUE is a constant defined in stm32f0xx.h file (default value
*             8 MHz) but the real value may vary depending on the variations
*             in voltage and temperature.
*
*         (**) HSE_VALUE is a constant defined in stm32f0xx.h file (default value
*              8 MHz), user has to ensure that HSE_VALUE is same as the real
*              frequency of the crystal used. Otherwise, this function may
*              have wrong result.
*
*         - The result of this function could be not correct when using fractional
*           value for HSE crystal.
* @param  None
* @retval None
*/
void SystemCoreClockUpdate (void)
{
uint32_t tmp = 0, pllmull = 0, pllsource = 0, prediv1factor = 0;
/* Get SYSCLK source -------------------------------------------------------*/
tmp = RCC->CFGR & RCC_CFGR_SWS;
switch (tmp)
{
case 0x00:  /* HSI used as system clock */
SystemCoreClock = HSI_VALUE;
break;
case 0x04:  /* HSE used as system clock */
SystemCoreClock = HSE_VALUE;
break;
case 0x08:  /* PLL used as system clock */
/* Get PLL clock source and multiplication factor ----------------------*/
pllmull = RCC->CFGR & RCC_CFGR_PLLMULL;
pllsource = RCC->CFGR & RCC_CFGR_PLLSRC;
pllmull = ( pllmull >> 18) + 2;
if (pllsource == 0x00)
{
/* HSI oscillator clock divided by 2 selected as PLL clock entry */
SystemCoreClock = (HSI_VALUE >> 1) * pllmull;
}
else
{
prediv1factor = (RCC->CFGR2 & RCC_CFGR2_PREDIV1) + 1;
/* HSE oscillator clock selected as PREDIV1 clock entry */
SystemCoreClock = (HSE_VALUE / prediv1factor) * pllmull;
}
break;
default: /* HSI used as system clock */
SystemCoreClock = HSI_VALUE;
break;
}
/* Compute HCLK clock frequency ----------------*/
/* Get HCLK prescaler */
tmp = AHBPrescTable[((RCC->CFGR & RCC_CFGR_HPRE) >> 4)];
/* HCLK clock frequency */
SystemCoreClock >>= tmp;
}
/**
* @brief  Configures the System clock frequency, AHB/APBx prescalers and Flash
*         settings.
* @note   This function should be called only once the RCC clock configuration
*         is reset to the default reset state (done in SystemInit() function).
* @param  None
* @retval None
*/
static void SetSysClock(void)
{
/******************************************************************************/
/*            PLL (clocked by HSI) used as System clock source                */
/******************************************************************************/
/* At this stage the HSI is already enabled and used as System clock source */
/* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
/* Enable Prefetch Buffer and set Flash Latency */
FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;
/* HCLK = SYSCLK / 1 */
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;
/* PCLK = HCLK / 1 */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;
/* PLL configuration */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_Div2 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL12);
/* Enable PLL */
RCC->CR |= RCC_CR_PLLON;
/* Wait till PLL is ready */
while((RCC->CR & RCC_CR_PLLRDY) == 0)
{
}
/* Select PLL as system clock source */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;
/* Wait till PLL is used as system clock source */
while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
{
}
}
/**
* @}
*/
/**
* @}
*/
/**
* @}
*/
/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

#include "Gpio.h"
/*
* LED3:PC9 ;  LED4:PC8
*
*/
void LED_init(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOC, ENABLE);
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOC, &GPIO_InitStructure);
}

4.GPIO配置好了，就只需在MAIN函数中调用一下，然后，在循环中，适当延长一段时间，并改变一下对外输出的电平LED就可以闪烁了，具体代码如下，这里笔者用的的是systick定时器进行延时，下次再对这个定时器做详细介绍。

/**
******************************************************************************
* @file    main.c
* @author  MCD Application Team
* @version V1.0.0
* @date    02-October-2013
* @brief   Main program body
******************************************************************************
* @attention
*
* 

*
* 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 "main.h"
#include "Gpio.h"
/** @addtogroup STM32F0308-Discovery_Demo
* @{
*/
/* Private typedef -----------------------------------------------------------*/
/* Private define ------------------------------------------------------------*/
/* Private macro -------------------------------------------------------------*/
/* Private variables ---------------------------------------------------------*/
static __IO uint32_t TimingDelay;
uint8_t BlinkSpeed = 0;
/* Private function prototypes -----------------------------------------------*/
/* Private functions ---------------------------------------------------------*/
/**
* @brief  Main program.
* @param  None
* @retval None
*/
int main(void)
{
RCC_ClocksTypeDef RCC_Clocks;
LED_init();
/* SysTick end of count event each 1ms */
RCC_GetClocksFreq(&RCC_Clocks);
SysTick_Config(RCC_Clocks.HCLK_Frequency / 1000);
/* Initiate Blink Speed variable */
BlinkSpeed = 1;
while(1){
if(GPIO_ReadOutputDataBit(GPIOC, GPIO_Pin_8) == Bit_SET)
{
GPIO_WriteBit(GPIOC, GPIO_Pin_8, Bit_RESET);
}
else{
GPIO_WriteBit(GPIOC, GPIO_Pin_8, Bit_SET);
}
if(GPIO_ReadOutputDataBit(GPIOC, GPIO_Pin_9) == Bit_SET)
{
GPIO_WriteBit(GPIOC, GPIO_Pin_9, Bit_RESET);
}
else{
GPIO_WriteBit(GPIOC, GPIO_Pin_9, Bit_SET);
}
Delay(300);
}
}
/**
* @brief  Inserts a delay time.
* @param  nTime: specifies the delay time length, in 1 ms.
* @retval None
*/
void Delay(__IO uint32_t nTime)
{
TimingDelay = nTime;
while(TimingDelay != 0);
}
/**
* @brief  Decrements the TimingDelay variable.
* @param  None
* @retval None
*/
void TimingDelay_Decrement(void)
{
if (TimingDelay != 0x00)
{
TimingDelay--;
}
}
#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****/


5、至此，LED可以闪烁了，对GPIO可以用初步认识了。