__HAL_RCC_SYSCLK_CONFIG macro
Macro to configure the system clock source.
Arguments
__RCC_SYSCLKSOURCE__
specifies the system clock source. This parameter can be one of the following values: - RCC_SYSCLKSOURCE_HSI: HSI oscillator is used as system clock source. - RCC_SYSCLKSOURCE_HSE: HSE oscillator is used as system clock source. - RCC_SYSCLKSOURCE_PLLCLK: PLL output is used as system clock source. - RCC_SYSCLKSOURCE_PLLRCLK: PLLR output is used as system clock source. This parameter is available only for STM32F446xx devices.