系统时钟(system clk)和cpu时钟(cpu clk)

References:

• STM32的时钟系统
• STM32系统时钟及配置方法
• 【STM32】系统时钟RCC详解(超详细，超全面)
• STM32 internal clocks
• Changing CPU frequency/clock in existing STM32H750 project
• What are system clock and CPU clock; and what are their functions?