We will use for our examples STM32CubeIDE released by ST and completely free. STM32CubeIDE is a development tool and supports multi operative system (SO), which is part of the STM32Cube software ecosystem. STM32CubeIDE allows using a single platform to configure peripherals, to generate/compile/debug the code for STM32 microcontrollers and microprocessors. The framework used is Eclipse®/CDT, as tool-chain for the development is used GCC toolchain and GDB for the debugging.
To start the project, you must first select the MCU and then initialize and configure the peripherals the user wants to use. At this point, the initialization code is generated. At any time, the user can go back and change initializations and configurations, without affecting the user code. We will dive into these steps with a simple example in the next paragraph.
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We must connect in series to LED a resistor. What resistance value must be considered to limit the current to 20 mA (see the formula below)?
R > 5 - 1.7/0.02 , where R > 165 ?
A good value of R is 220 ?.
Now we must be able to turn off the led, to do it we need a switch to connect and disconnect the power supply as shown below.
In this case when the switch is closed the Led is ON, when the switch is open the Led is OFF. This can be easily done with a Nucleo board by configuring a GPIO (General Purpose Input Output) pin.
The steps required to configure a core board are explained below. Obviously, this is a very simple practical example, but peripherals, communication protocols and anything else can be configured in a similar way.
As already said, we will use for our examples a NUCLEO-L053R8 board. For our examples, so also a Windows PC is required. The ST-Link USB connector is used both for serial data communications, and firmware downloading and debugging on the MCU. A Type-A to mini-B USB cable must be connected between the board and the computer. The USART2 peripheral uses PA2 and PA3 pins, which are wired to the ST-Link connector. In addition, USART2 is selected to communicate with the PC via the ST-Link Virtual COM Port. A tool that emulates the serial communication terminal is necessary to view received messages and send them. You can download many open-source tools as Tera Term. In this way, you can display on PC the messages received from the board over the virtual communication Port and the other way around.
In this paragraph, we will initialize the peripherals using STM32CubeMX. The STM32CubeMX tool to create the necessary config. files to enable drivers of peripheral used (for more detail read “UM1718 - User manual STM32CubeMX for STM32 configuration and initialization C code generation.”).
The user code must be inserted between the "USER CODE BEGIN" and "USER CODE END" so that if you go to regenerate the initializations that part of the code is not deleted or overwritten. As shown in the code below, the simplest way is to use the function:
Note This function is declared as __weak to be overwritten in case of other implementations in a user file.
- Delay: specifies the delay time length, in milliseconds.
So, in our case GPIOx is GPIOA and the GPIO_PIN is GPIO_PIN_9 (see below).
int main(void) { /* USER CODE BEGIN 1 */ /* USER CODE END 1 */ /* MCU Configuration--------------------------------------------------------*/ /* Reset of all peripherals, Initializes the Flash interface and the Systick. */ HAL_Init(); /* USER CODE BEGIN Init */ /* USER CODE END Init */ /* Configure the system clock */ SystemClock_Config(); /* USER CODE BEGIN SysInit */ /* USER CODE END SysInit */ /* Initialize all configured peripherals */ MX_GPIO_Init(); MX_TIM2_Init(); /* USER CODE BEGIN 2 */ /* USER CODE END 2 */ /* Infinite loop */ /* USER CODE BEGIN WHILE */ while (1) { HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_9); HAL_Delay(1000); /* USER CODE END WHILE */ /* USER CODE BEGIN 3 */ } /* USER CODE END 3 */ }
Now we are ready to compile and run the project:
Another simple way is to use the function
Note This function uses GPIOx_BSRR register to allow atomic read/modify accesses. In this way, there is no risk of an IRQ occurring between the read and the modified access.
Note that GPIOE is not available on all devices.
This parameter can be one of GPIO_PIN_x where x can be (0..15).
All port bits are not necessarily available on all GPIOs.
This parameter can be one of the GPIO_PinState enum values:
So, in our case GPIOx is GPIOA and the GPIO_PIN is GPIO_PIN_9 and the pin state changes between 0 (LOW or CLEAR) and 1 (HIGH or SET).
In this case, the code is the following:
while (1) { HAL_GPIO_WritePin(GPIOA, GPIO_PIN_9,0); HAL_Delay(1000); HAL_GPIO_WritePin(GPIOA, GPIO_PIN_9,1); /* USER CODE END WHILE */ /* USER CODE BEGIN 3 */ } /* USER CODE END 3 */ }
There are many other ways to blink an Led such as PWM, Interrupts etc. and will discuss it in the upcoming lectures. Thanks for reading.
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