STM32F103ZGT6 ,use HSI, by PLL to 64MHZ,-->MCU no response by PLL to 32MHZ,-->MCU OK Where do i need to check？

[zyimi]

FLASH->ACR |= FLASH_ACR_PRFTBE;

  /* Flash 2 wait state */

  FLASH->ACR &= (uint32_t)((uint32_t)~FLASH_ACR_LATENCY);

  FLASH->ACR |= (uint32_t)FLASH_ACR_LATENCY_2;   

[TDK]

When increasing clock speed, increase flash latency prior to the clock change to avoid an invalid intermediate state. Also do it in a single operation to avoid an invalid intermediate state.