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Keil, initial clock configuration.

Question asked by jargin.matt on Nov 10, 2012
Latest reply on Nov 11, 2012 by Clive One
I'm writing my own USART code to work with USART1. I need to know what the start-up code that keil gives you sets the clock initially at. I can change it manually but id like to know where the code is. Also USART1 is running off of APB2 clock, how do I figure out what the clock speed is so I can figure out what I should write in the USART_BRR register? 

As I understand it, APBx clock comes from the system clock (HSI,HSE,PLL), then through AHB prescaler (if is has one) then through the APBx prescaler. Is this correct? 

I would like to edit the keil start up code to enable the HSI with PLL to make system clock 168Mhz, then have APB2 clock run at 12Mhz (There is a table for BRR register at this speed). 

I'm using the system_stm32f4xx.c and startup_stm32f4xx.c.

Thanks for the advise.