ST STM32F31xx

UM1581
Reset and clock control (RCC)
DocID023800 Rev 1
329/584
18.2.8.6 RCC_RTCCLKConfig
Function Name
void RCC_RTCCLKConfig ( uint32_t RCC_RTCCLKSource)
Function Description
Configures the RTC clock (RTCCLK).
Parameters
 RCC_RTCCLKSource : specifies the RTC clock source.
This parameter can be one of the following values:
 RCC_RTCCLKSource_LSE : LSE selected as RTC
clock
 RCC_RTCCLKSource_LSI : LSI selected as RTC clock
 RCC_RTCCLKSource_HSE_Div32 : HSE divided by
32 selected as RTC clock
Return values
 None.
Notes
 As the RTC clock configuration bits are in the Backup domain
and write access is denied to this domain after reset, you
have to enable write access using
PWR_BackupAccessCmd(ENABLE) function before to
configure the RTC clock source (to be done once after reset).
 Once the RTC clock is configured it can't be changed unless
the RTC is reset using RCC_BackupResetCmd function, or
by a Power On Reset (POR)
 If the LSE or LSI is used as RTC clock source, the RTC
continues to work in STOP and STANDBY modes, and can
be used as wakeup source. However, when the HSE clock is
used as RTC clock source, the RTC cannot be used in STOP
and STANDBY modes.
 The maximum input clock frequency for RTC is 2MHz (when
using HSE as RTC clock source).
18.2.8.7 RCC_I2SCLKConfig
Function Name
void RCC_I2SCLKConfig ( uint32_t RCC_I2SCLKSource)
Function Description
Configures the I2S clock source (I2SCLK).
Parameters
 RCC_I2SCLKSource : specifies the I2S clock source. This
parameter can be one of the following values:
 RCC_I2S2CLKSource_SYSCLK : SYSCLK clock used
as I2S clock source
 RCC_I2S2CLKSource_Ext : External clock mapped on
the I2S_CKIN pin used as I2S clock source
Return values
 None.
Notes
 This function must be called before enabling the SPI2 and
SPI3 clocks.