Thank you for your reply.
- Why would you like to reduce the system clock from 80MHz to 8 MHz?
For Reduce Power consumption.
- Why did you decide to use different settings than advised? Those setting will not produce an 8 MHz system clock.
Because the nucleo-L476RG board does not have an external crystal to use HSE.
MSI is used for PLL in default setting of mbedOS, so I tried the configuration with MSI.
I think my setting can produce 8MHz system clock. But this setting did not work.
- The working speed of peripherals depends on the system clock frequency. To get the desired bit rate of a UART (
BufferedSerial) the mbed system software divides the system clock frequency by some predefined set of coefficients. If the system clock is too low than it could happen that the required bit rate cannot be achieved.
I asked STM if the 115.2kHz UART work on my settings, (e.g. 8MHz clock, 16 over sampling and so on), and got answer YES.
So I guessed the reason why UART did not work is there are some setting I should do in addition I did.
Unfortunately, I don’t know how to make it work without using the PLL block
OK. I understood the system clock setting of mbed assuming to use PLL block.