Microcontroller Programming | Cortex-M4 | stm32f4 Discovery Board

Saturday, February 22, 2020

4. GPIO (using LED and Push Button)

I this example we are using Green LED on our stem32f4 Discovery Board. It will turn on, once the
push Button is pressed.

Steps:
1. Enable clock for LED:
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
2. Enable clock for push Button:
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
3. Configure Pins (LED and push Button)
4. We can then use the LED and Button

Example:

3. Setting System Clock Frequency (Excel Utility)

In this example, I am using Excel Utility

Steps:
1. After creating any project with Atollic TrueStudio, the HSE value is automatically set to 25
MHz, which is not correct. First, we have to edit it to 8 MHz. For that go to stm32f4xx.h and
find HSE_VALUE. Change there the value to 8000000.

2. Open the Excel File

Here we can see HSE value is 8 (i.e. 8 MHz), we always have to use this value. stm32f4 Discovery

Board have external Oscillator whose frequency is 8 MHz. Our Discovery have highest frequency

of 168 MHz. We can choose here our own frequency. In my Example I'm setting the value to 48

MHz.

3. Enter HCLK frequency value

4. Click on Run and choose PLL(HSE) as source clock and then click on OK.

5. Click on Generate. A file (system_stm32f4xx.c) in the same folder with new clock frequency

will be generated.

6. Copy that file. Then go to your project on Atollic TrueStudio. Replace there the

file system_stm32f4xx.c with new one we have generated.

Ready to Go :)

2. Using Random Number Generator (RNG)

Cortex-M4 features 32 bit RNG

Steps:

Activating clock for RNG: RCC_AHB2PeriphClockCmd(RCC_AHB2Periph_RNG, ENABLE);
Activating the RNG itself: RNG_Cmd(ENABLE);
Before calling for random number from RNG, we have to check whether the Data is ready with RNG Flag: RNG_GetFlagStatus(RNG_FLAG_DRDY)
Getting generated numbers: RNG_GetRandomNumber()

Example: