ST STM32F2 User Manual page 444

HAL RCC Generic Driver
HSE Config
RCC_HSE_OFF
RCC_HSE_ON
RCC_HSE_BYPASS
HSE Configuration
__HAL_RCC_HSE_CONFIG
HSI Config
RCC_HSI_OFF
RCC_HSI_ON
RCC_HSICALIBRATION_DEFAULT
HSI Configuration
__HAL_RCC_HSI_ENABLE
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RCC_PLLSOURCE_HSE: HSE oscillator is
used as PLL clock source.
Description:
Macro to configure the External High Speed oscillator
(HSE).
Parameters:
__STATE__: specifies the new state of the HSE. This
parameter can be one of the following values:
RCC_HSE_OFF: turn OFF the HSE oscillator,
HSERDY flag goes low after 6 HSE oscillator
clock cycles.
RCC_HSE_ON: turn ON the HSE oscillator.
RCC_HSE_BYPASS: HSE oscillator bypassed
with external clock.
Notes:
Transition HSE Bypass to HSE On and HSE On to
HSE Bypass are not supported by this macro. User
should request a transition to HSE Off first and then
HSE On or HSE Bypass. After enabling the HSE
(RCC_HSE_ON or RCC_HSE_Bypass), the
application software should wait on HSERDY flag to
be set indicating that HSE clock is stable and can be
used to clock the PLL and/or system clock. HSE state
can not be changed if it is used directly or through the
PLL as system clock. In this case, you have to select
another source of the system clock then change the
HSE state (ex. disable it). The HSE is stopped by
hardware when entering STOP and STANDBY modes.
This function reset the CSSON bit, so if the clock
security system(CSS) was previously enabled you
have to enable it again after calling this function.
DocID028236 Rev 2
Notes:
The HSI is stopped by hardware
when entering STOP and
STANDBY modes. It is used
(enabled by hardware) as
UM1940