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
The most basic thing one would do with an MCU would be how to control the IO pins right? So how do we program the GPIO pins on STM32F4Discovery board? Let's take a look at it now, First and foremost we need to add stm32f4xx_gpio.h and stm32f4xx_rcc.h header files to be included in the project. Once that is done we must enable clock to the port (whichever port you would like to use) Each peripheral bus is detailed in the datasheet and we can use this information to enable system clock programmatically based on our application. Then we have to set parameters for configuring GPIO pins The various options are self explanatory.You can adjust the settings based on your application. Now lets try to toggle pin14 from PORTD which is an onboard LED on our discovery board. We've done it! Now you can compile it and see the onboard LED blinking ON and OFF! So the final code looks something like