Using PWM on STM32 with RT-Thread

This article describes how to use PWM waveform output on a platform equipped with the RT-Thread operating system, including the application, configuration, and driver addition of PWM. A code example verified on the ZhiDian atom STM32L475 pandora development board is provided.

Introduction to Hardware Platform

This article is based on the ZhiDian atom STM32L475 pandora development board, providing specific application example codes for PWM. Due to the generality of the RT-Thread upper application API, these codes are not limited to specific hardware platforms, and users can easily port them to other platforms.

STM32L475 pandora is a development board launched by ZhiDian atom based on the ARM Cortex-M4 core, with a maximum frequency of 80MHz. This development board has rich onboard resources that can fully utilize the chip performance of STM32L475.

Using PWM

Open PWM Channel in menuconfig

Open the Env tool and use the menuconfig tool to configure the project. Enter menuconfig in the Env command line to access the configuration interface. In the menuconfig configuration interface, select Hardware Driver Config ---> On-chip Peripheral Drivers ---> Enable pwm ---> Enable timer2 output pwm as shown in the figure below:

After selecting the PWM channel to be used, save and exit. Use scons --target=mdk5 to generate the mdk5 project, open the project to compile and download the program. Enter the command list_device in the terminal to see that the PWM2 device has been successfully added, as shown in the figure below:

Using PWM to Output Waveform

The application can access the PWM device hardware through the device management interface provided by RT-Thread, as shown in the following relevant interfaces:

For a detailed description of the interface parameters, please refer to the official website PWM device

🔗Link:

https://www.rt-thread.org/document/site/programming-manual/device/pwm/pwm/

(Please copy the above link to an external browser to open)

Steps to Use PWM Device

The specific usage of the PWM device can be referred to in the following steps:

Initialize the PWM device.

⚪ Use rt_device_find to find the specified PWM device.

⚪ Use rt_pwm_set to set the default PWM cycle and pulse width of the channel.

⚪ Use rt_pwm_enable to enable the PWM channel that needs to output the waveform.
Use the PWM device to output the waveform.

⚪ Use rt_pwm_set to output a specific waveform.
Close the PWM output channel.

⚪ When the PWM channel output waveform is no longer needed, rt_pwm_disable can be called to close the corresponding output channel.

The code is as follows: Swipe👉 to view all

 1#define PWM_DEV_NAME            "pwm2"  /* PWM device name */
 2#define PWM_DEV_CHANNEL         3       /* PWM channel */
 3#define THREAD_PRIORITY         25      /* Thread priority */
 4#define THREAD_STACK_SIZE       512     /* Thread stack size */
 5#define THREAD_TIMESLICE        5       /* Thread time slice size */
 6
 7static rt_thread_t tid1 = RT_NULL;      /* Thread handle */
 8struct rt_device_pwm *pwm_dev;          /* PWM device handle */
 9static rt_uint32_t period = 500000;     /* Period is 0.5ms, unit is nanoseconds ns */
10static rt_uint32_t pulse = 0;           /* PWM pulse width value increase and decrease direction */
11
12/* Entry function of thread pwm_entry */
13static void pwm_entry(void *parameter)
14{
15    rt_uint32_t count = 0;
16
17    while (count++ &lt; 1000)
18    {
19        rt_thread_mdelay(50);
20        /* step 2, set PWM period and pulse width, output specific waveform */
21        rt_pwm_set(pwm_dev, PWM_DEV_CHANNEL, period, pulse++);
22    }
23    /* step 3, if the channel is no longer used, the PWM channel output can be turned off */
24    rt_pwm_disable(pwm_dev, PWM_DEV_CHANNEL);
25}
26
27static int pwm_test(int argc, char *argv[])
28{
29    /* step 1.1, find PWM device */
30    pwm_dev = (struct rt_device_pwm *)rt_device_find(PWM_DEV_NAME);
31    if (pwm_dev == RT_NULL)
32    {
33        rt_kprintf("pwm sample run failed! can't find %s device!\n", PWM_DEV_NAME);
34        return RT_ERROR;
35    }
36
37    /* step 1.2, set default values for PWM period and pulse width */
38    rt_pwm_set(pwm_dev, PWM_DEV_CHANNEL, period, pulse);
39    /* step 1.3, enable the output channel of the PWM device */
40    rt_pwm_enable(pwm_dev, PWM_DEV_CHANNEL);
41
42    /* Create thread, name it pwm_thread, entry is pwm_entry*/
43    tid1 = rt_thread_create("pwm_thread",
44                             pwm_entry,
45                             RT_NULL,
46                             THREAD_STACK_SIZE,
47                             THREAD_PRIORITY,
48                             THREAD_TIMESLICE);
49
50    /* If the thread control block is obtained, start this thread */
51    if (tid1 != RT_NULL)
52        rt_thread_startup(tid1);
53
54    return RT_EOK;
55}
56/* Export to msh command list */
57MSH_CMD_EXPORT(pwm_test, pwm sample);

Compile and download the program. Enter the help command in the terminal to see that the pwm_test command has been successfully exported, as shown in the figure below:

Running the PWM Test Program

To run the PWM test program, you need to enter pwm_test in the terminal. Since the output of PWM2 channel 3 of this BSP is not connected to the peripheral, the phenomenon cannot be visually observed. Therefore, a logic analyzer is used to capture the PWM output waveform, which is shown in the figure below:

The waveform captured from the logic analyzer shows that the PWM waveform has been successfully output.

Adding PWM Driver

If the BSP used does not provide PWM channel configuration options in menuconfig, you will need to add the PWM driver yourself. Below is an explanation of how to add the PWM driver yourself.

Check if the driver file supports PWM

Enter rt-thread\bsp\stm32\libraries\HAL_Drivers directory to check whether the drv_pwm.c file supports the corresponding PWM peripheral output. Check whether the driver file supports the corresponding PWM peripherals (PWM1, 2, n)

Check whether the driver file supports the corresponding PWM output channels (1, 2, 3, 4)

Initialize PWM Channel Pins

Enter rt-thread\bsp\stm32l475-atk-pandora\board\CubeMX_Config directory and double-click to open STM32L475VE.ioc file to initialize the pins corresponding to the PWM channel, taking PWM2 channel 3 as an example, as shown in the figure below:

Click the GENERATE CODE button to generate the code. Although STM32CubeMX generates multiple files for initializing peripherals, RT-Thread only uses the STM32CubeMX generated stm32fxx_hal_msp.c file and stm32fxx_hal_conf.h file. The generated PWM code is as follows:

Configure Kconfig File

Enter rt-thread\bsp\stm32l475-atk-pandora\board directory and add Kconfig options, as shown in the figure below:

Use scons --target=mdk5 command to generate the mdk5 project, open the project and compile. If the project prompts that PWMn_CONFIG is undefined.

You can define it in stm32/libraries/HAL_Drivers/config/f4/pwm_config.h as shown in the figure below:

After completing the above steps, you can add the supported PWM output channels in the menuconfig menu. As for how to use the PWM channel to output waveforms, please refer to the previous chapter.

At this point, the introduction to how to use PWM on a platform equipped with the RT-Thread operating system is coming to an end.

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