What will happen if I turn on multiple System Clock source on(MSI - HSI - HSE )

[KHuyn]

Hello every one.

I am working with the STM32L4R5ZI. By default, it will uses MSI as the system clock source at 4Mhz.

My question is: what will happen if I turn on HSI or/and HSE without turning the other clock source off?

Thank you in advance?

[Tesla DeLorean]

You'll have multiple clocks ticking, one of which you are clocking the rest of the part with.​

[Piranha]

Turning on/off oscillators and selecting system clock are two different and to some extent unrelated things. But of course the oscillator, selected as a system clock at that particular moment, must be on.

[KHuyn]

Thank you for your reply, but I don't quit get your explanation :(

[KHuyn]

Sorry, my question was unclear. Yes, I was asking what happen when more than 2 clock sources are selected, what is the SYSCLK will be eventually?

Say that I set the HSION = 1 in RCC->CR to select HSI as my desired clock source, but forgot to turn off MSION in my code(which is selected as default).

Hope that is more clear.

Thank

[Piranha · Accepted solution]

Setting HSION bit in RCC_CR register only turns on that oscillator, but doesn't select it as a system clock. The same is true for other oscillators. System clock is selected with RCC_CFGR register SW bits and You can't select multiple sources there.

[Tesla DeLorean]

The mux can select only one source. You can have other clocks​ running.

[KHuyn]

Thank you. That clears my mind.

[KHuyn]

Thank you, I got it now.