So you have got an STM32F4 discovery board in your hands. I can surely assume one of the reason you got this nifty little development board is it's computing capability at 168MHz. However if you are not cautious, you may not achieve the maximum clock speed the device could achieve.If u are not careful (sometimes it happens) the controller would run at lower clock.Obviously that is not a bad thing in power critical applications.Here are some steps to ensure the system is running at its peak performance STEP 1: Download clock configuration tool from ST, file named AN3988 http://www.st.com/internet/mcu/product/252149.jsp STEP 2: Open the clock configuration tool using excel and change HCLK to 168 MHz.You can select on other options and PLL frequencies also (Know what you are doing else leave it as it is).Click generate.If values are OK then no errors would be shown.Then click on generate.Then close the excel file.You should have got a system_stm32f4xx.c file in the folder.U