```typedef struct
{
  uint32_t SYSCLK_Frequency;  /*!< returns SYSCLK clock frequency expressed in Hz */
  uint32_t HCLK_Frequency;    /*!< returns HCLK clock frequency expressed in Hz */
  uint32_t PCLK1_Frequency;   /*!< returns PCLK1 clock frequency expressed in Hz */
  uint32_t PCLK2_Frequency;   /*!< returns PCLK2 clock frequency expressed in Hz */
  uint32_t ADCCLK_Frequency;  /*!< returns ADCCLK clock frequency expressed in Hz */
}RCC_ClocksTypeDef;```

I can use SystemCoreClock or SystemCoreClock/2 instead, 72000000/2=36000000, but this is me supposing it is the relation between SysClock and APB1 clock. Looking at the datasheet it says: "AHB/APB bridges
The two AHB/APB bridges provide full synchronous connections between the AHB and the
2 APB buses. APB1 is limited to 36 MHz, APB2 operates at full speed (72 MHz)." it doesn't say it is half of sysclock... at least I didn't find it :s