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I am confused with the clock system on my STM32F7 device (Cortex-M7 microcontroller from STMicroelectronics). The reference manual does not clarify the differences between these clocks sufficiently:
The reference manual reads in chapter << 5.2 Clocks >> "The RCC feeds the external clock of the Cortex System Timer (SysTick) with the AHB clock (HCLK) divided by 8."
This statement contradicts the figure from CubeMX. Notice that in CubeMX I can choose myself the prescaler from HCLK to 'Cortex System Timer'. It is not necessarily a division by 8.
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STM32F7 devices embed two oscillators for use with an external crystal or resonator: a high-speed external 4 to 26 MHz oscillator (HSE) with a clock security system and a low-speed external 32.768 kHz oscillator (LSE) also with a clock security system.
The HSE crystal has the advantage of producing a very accurate rate on the main clock. The HSI clock signal is generated from an internal oscillator and can be used directly as a system clock, or used as PLL input. The HSI RC oscillator has the advantage of providing a clock source at low cost (no external components).
The MSI which is the system clock used at startup from Reset, Standby or Shutdown modes, is programmable. It supports 12 ranges from 100 kHz to 48 MHz, selected through the MSIRANGE control bits.
Normally the only difference between HCLK and FCLK is that :
HCLK is the main CPU clock, also used for AHB interface. It can be gated when the CPU is sleeping (WFI for example)FCLK is synchronous to HCLK but is not gated when the CPU goes to sleep, so that it can awake in case of interrupt.
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