Martin Johnson / STM32F3-Discovery

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System AHB, APB1 and APB2 busses clocks configuration functions
Functions

System AHB, APB1 and APB2 busses clocks configuration functions
[RCC_Private_Functions]

System, AHB and APB busses clocks configuration functions. More...

Functions

void RCC_SYSCLKConfig (uint32_t RCC_SYSCLKSource)
 Configures the system clock (SYSCLK).
uint8_t RCC_GetSYSCLKSource (void)
 Returns the clock source used as system clock.
void RCC_HCLKConfig (uint32_t RCC_SYSCLK)
 Configures the AHB clock (HCLK).
void RCC_PCLK1Config (uint32_t RCC_HCLK)
 Configures the Low Speed APB clock (PCLK1).
void RCC_PCLK2Config (uint32_t RCC_HCLK)
 Configures the High Speed APB clock (PCLK2).
void RCC_GetClocksFreq (RCC_ClocksTypeDef *RCC_Clocks)
 Returns the frequencies of the System, AHB, APB2 and APB1 busses clocks.

Detailed Description

System, AHB and APB busses clocks configuration functions. 

 ===============================================================================
  ##### System, AHB, APB1 and APB2 busses clocks configuration functions #####
 ===============================================================================  
    [..] This section provide functions allowing to configure the System, AHB, APB1 and 
         APB2 busses clocks.
         (#) Several clock sources can be used to drive the System clock (SYSCLK): HSI,
             HSE and PLL.
             The AHB clock (HCLK) is derived from System clock through configurable prescaler
             and used to clock the CPU, memory and peripherals mapped on AHB bus (DMA and GPIO).
             APB1 (PCLK1) and APB2 (PCLK2) clocks are derived from AHB clock through 
             configurable prescalers and used to clock the peripherals mapped on these busses.
             You can use "RCC_GetClocksFreq()" function to retrieve the frequencies of these clocks.

         (#) The maximum frequency of the SYSCLK, HCLK, PCLK1 and PCLK2 is 72 MHz.
             Depending on the maximum frequency, the FLASH wait states (WS) should be 
             adapted accordingly:
        +---------------------------------+
        |  Wait states  |   HCLK clock    |
        |   (Latency)   | frequency (MHz) |
        |-------------- |-----------------|             
        |0WS(1CPU cycle)| 0 < HCLK <= 24  |
        |---------------|-----------------| 
        |1WS(2CPU cycle)|24 < HCLK <=48   |
        |---------------|-----------------| 
        |2WS(3CPU cycle)|48 < HCLK <= 72  |
        +---------------------------------+

         (#) After reset, the System clock source is the HSI (8 MHz) with 0 WS and 
             prefetch is disabled.
        [..]
         (@) All the peripheral clocks are derived from the System clock (SYSCLK) 
             except:
             (+@) The FLASH program/erase clock  which is always HSI 8MHz clock.
             (+@) The USB 48 MHz clock which is derived from the PLL VCO clock.
             (+@) The USART clock which can be derived as well from HSI 8MHz, LSI or LSE.
             (+@) The I2C clock which can be derived as well from HSI 8MHz clock.
             (+@) The ADC clock which is derived from PLL output.
             (+@) The RTC clock which is derived from the LSE, LSI or 1 MHz HSE_RTC 
                  (HSE divided by a programmable prescaler). The System clock (SYSCLK) 
                  frequency must be higher or equal to the RTC clock frequency.
             (+@) IWDG clock which is always the LSI clock.
    [..] It is recommended to use the following software sequences to tune the number
         of wait states needed to access the Flash memory with the CPU frequency (HCLK).
         (+) Increasing the CPU frequency
            (++) Program the Flash Prefetch buffer, using "FLASH_PrefetchBufferCmd(ENABLE)" 
                 function
            (++) Check that Flash Prefetch buffer activation is taken into account by 
                 reading FLASH_ACR using the FLASH_GetPrefetchBufferStatus() function
            (++) Program Flash WS to 1 or 2, using "FLASH_SetLatency()" function
            (++) Check that the new number of WS is taken into account by reading FLASH_ACR
            (++) Modify the CPU clock source, using "RCC_SYSCLKConfig()" function
            (++) If needed, modify the CPU clock prescaler by using "RCC_HCLKConfig()" function
            (++) Check that the new CPU clock source is taken into account by reading 
                 the clock source status, using "RCC_GetSYSCLKSource()" function 
         (+) Decreasing the CPU frequency
            (++) Modify the CPU clock source, using "RCC_SYSCLKConfig()" function
            (++) If needed, modify the CPU clock prescaler by using "RCC_HCLKConfig()" function
            (++) Check that the new CPU clock source is taken into account by reading 
                 the clock source status, using "RCC_GetSYSCLKSource()" function
            (++) Program the new number of WS, using "FLASH_SetLatency()" function
            (++) Check that the new number of WS is taken into account by reading FLASH_ACR
            (++) Disable the Flash Prefetch buffer using "FLASH_PrefetchBufferCmd(DISABLE)" 
                 function
            (++) Check that Flash Prefetch buffer deactivation is taken into account by reading FLASH_ACR
                 using the FLASH_GetPrefetchBufferStatus() function.

Function Documentation

void RCC_GetClocksFreq ( RCC_ClocksTypeDef *  RCC_Clocks )

Returns the frequencies of the System, AHB, APB2 and APB1 busses clocks.

Note:
This function returns the frequencies of : System, AHB, APB2 and APB1 busses clocks, ADC1/2/3/4 clocks, USART1/2/3/4/5 clocks, I2C1/2 clocks and TIM1/8 Clocks.
The frequency returned by this function is not the real frequency in the chip. It is calculated based on the predefined constant and the source selected by RCC_SYSCLKConfig().
If SYSCLK source is HSI, function returns constant HSI_VALUE(*)
If SYSCLK source is HSE, function returns constant HSE_VALUE(**)
If SYSCLK source is PLL, function returns constant HSE_VALUE(**) or HSI_VALUE(*) multiplied by the PLL factors.
(*) HSI_VALUE is a constant defined in stm32f30x.h file (default value 8 MHz) but the real value may vary depending on the variations in voltage and temperature, refer to RCC_AdjustHSICalibrationValue().
(**) HSE_VALUE is a constant defined in stm32f30x.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 return wrong result.
The result of this function could be not correct when using fractional value for HSE crystal.
Parameters:
RCC_Clocks,:pointer to a RCC_ClocksTypeDef structure which will hold the clocks frequencies.
Note:
This function can be used by the user application to compute the baudrate for the communication peripherals or configure other parameters.
Each time SYSCLK, HCLK, PCLK1 and/or PCLK2 clock changes, this function must be called to update the structure's field. Otherwise, any configuration based on this function will be incorrect.
Return values:
None

Definition at line 852 of file stm32f30x_rcc.c.

uint8_t RCC_GetSYSCLKSource ( void   )

Returns the clock source used as system clock.

Parameters:
None
Return values:
Theclock source used as system clock. The returned value can be one of the following values:

  • 0x00: HSI used as system clock
  • 0x04: HSE used as system clock
  • 0x08: PLL used as system clock

Definition at line 709 of file stm32f30x_rcc.c.

void RCC_HCLKConfig ( uint32_t  RCC_SYSCLK )

Configures the AHB clock (HCLK).

Note:
Depending on the device voltage range, the software has to set correctly these bits to ensure that the system frequency does not exceed the maximum allowed frequency (for more details refer to section above "CPU, AHB and APB busses clocks configuration functions").
Parameters:
RCC_SYSCLK,:defines the AHB clock divider. This clock is derived from the system clock (SYSCLK). This parameter can be one of the following values:

  • RCC_SYSCLK_Div1: AHB clock = SYSCLK
  • RCC_SYSCLK_Div2: AHB clock = SYSCLK/2
  • RCC_SYSCLK_Div4: AHB clock = SYSCLK/4
  • RCC_SYSCLK_Div8: AHB clock = SYSCLK/8
  • RCC_SYSCLK_Div16: AHB clock = SYSCLK/16
  • RCC_SYSCLK_Div64: AHB clock = SYSCLK/64
  • RCC_SYSCLK_Div128: AHB clock = SYSCLK/128
  • RCC_SYSCLK_Div256: AHB clock = SYSCLK/256
  • RCC_SYSCLK_Div512: AHB clock = SYSCLK/512
Return values:
None

Definition at line 734 of file stm32f30x_rcc.c.

void RCC_PCLK1Config ( uint32_t  RCC_HCLK )

Configures the Low Speed APB clock (PCLK1).

Parameters:
RCC_HCLK,:defines the APB1 clock divider. This clock is derived from the AHB clock (HCLK). This parameter can be one of the following values:

  • RCC_HCLK_Div1: APB1 clock = HCLK
  • RCC_HCLK_Div2: APB1 clock = HCLK/2
  • RCC_HCLK_Div4: APB1 clock = HCLK/4
  • RCC_HCLK_Div8: APB1 clock = HCLK/8
  • RCC_HCLK_Div16: APB1 clock = HCLK/16
Return values:
None

Definition at line 765 of file stm32f30x_rcc.c.

void RCC_PCLK2Config ( uint32_t  RCC_HCLK )

Configures the High Speed APB clock (PCLK2).

Parameters:
RCC_HCLK,:defines the APB2 clock divider. This clock is derived from the AHB clock (HCLK). This parameter can be one of the following values:

  • RCC_HCLK_Div1: APB2 clock = HCLK
  • RCC_HCLK_Div2: APB2 clock = HCLK/2
  • RCC_HCLK_Div4: APB2 clock = HCLK/4
  • RCC_HCLK_Div8: APB2 clock = HCLK/8
  • RCC_HCLK_Div16: APB2 clock = HCLK/16
Return values:
None

Definition at line 795 of file stm32f30x_rcc.c.

void RCC_SYSCLKConfig ( uint32_t  RCC_SYSCLKSource )

Configures the system clock (SYSCLK).

Note:
The HSI is used (enabled by hardware) as system clock source after startup from Reset, wake-up from STOP and STANDBY mode, or in case of failure of the HSE used directly or indirectly as system clock (if the Clock Security System CSS is enabled).
A switch from one clock source to another occurs only if the target clock source is ready (clock stable after startup delay or PLL locked). If a clock source which is not yet ready is selected, the switch will occur when the clock source will be ready. You can use RCC_GetSYSCLKSource() function to know which clock is currently used as system clock source.
Parameters:
RCC_SYSCLKSource,:specifies the clock source used as system clock source This parameter can be one of the following values:

  • RCC_SYSCLKSource_HSI: HSI selected as system clock source
  • RCC_SYSCLKSource_HSE: HSE selected as system clock source
  • RCC_SYSCLKSource_PLLCLK: PLL selected as system clock source
Return values:
None

Definition at line 681 of file stm32f30x_rcc.c.

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