STM32F407 mishmash

Clock Configuration for STM32F407 The selection of clock that I used for STM32F407 can be explained by below diagram and steps: - Steps for clock setting: - Decide if frequency source, HSE (high speed external = crystal of 8MHz) or HSI (high speed internal = 16MHz) to be used. Crystal have high frequency stability and their variations can be measured in ppm (about 20 ppm) (if measured in %, it will be 0.002%), but internal frequency source vary quite a bit, when temperature changes. They are OK for UART, SPI, I2C, PWM and ADC. But the frequency variation is not good for CAN, UAB, ETHERNET etc. Select "M" (divisor) as 8 for HSE and 16 for HSI. So output is 1MHz. This 1MHz is input to PLL. The 1MHz is not multiplied by "N". "N" is selected as 336. There are 2 divisors = P and Q. "P" is selected as 2 and "Q" is selected as 7 to get output of 168MHz and 48MHz respectively. The 168MHz then goes to AHB divisor, which is s