How to generate PWM and use timer interrupt at the same time?

[M7890.1]

I am using the Bluepill board. I want to generate PWM signal on Timer2 and set up a timer interrupt at 20ms interval on Timer3. I realized that the PWM signal cannot be generated if I set up the timer interrupt on Timer3. How do I solve this problem?

[TDK]

You can have PWM generation on one timer and update interrupt on another timer at the same time. What issue are you running into? They are independent.

[M7890.1]

Yes. They should be independent. So I was having these 3 lines before my while loop:

HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_1);	// start PWM signal
HAL_TIM_PWM_Start(&htim2, TIM_CHANNEL_2);
 
HAL_TIM_Base_Start_IT(&htim3);

I have set my PWM pulse width to 1ms. When I take a look at the output, the PWM output a single pulse of 1ms and it becomes zero after that (most probably after timer3 being started). If I remove HAL_TIM_Base_Start_IT(&htim3); from my code, the PWM signal can be generated without problem.

[M7890.1]

The PWM output is not affected if I start timer3 without interrupt.

[TDK]

Shouldn’t be affected either way. I suspect you’re doing something in the period elapsed callback.l that stops the PWM. Regardless, you can debug and examine the registers to see why PWM stopped. Has the be a reason.

[M7890.1]

Yes. I am doing something when timer interrupt fired.

void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef* htim) {
	float error;
	static float past_error;
	float roll_pid_p;
	static float roll_pid_i = 0;
	float roll_pid_d;
	float roll_pid;
 
	uint16_t left_pwm, right_pwm;
 
	const uint16_t max_pwm = 1800;
	const uint16_t thrust = 1200;
 
	// GET ROLL ANGLE
	mpu6050_read_data();
	mpu6050_calc_angle();
 
	// COMPUTE PID
	error = comp_roll - 0;	// setpoint = 0
 
	roll_pid_p = pid_coef[0] * error;
	roll_pid_i = roll_pid_i + pid_coef[1] * error;
	roll_pid_d = pid_coef[2] * ((error - past_error) / 0.02);// 0.02 is update rate
 
	roll_pid = roll_pid_p + roll_pid_i + roll_pid_d;
 
//	if (roll_pid > max_pwm - thrust)
//		roll_pid = max_pwm - thrust;
//	else if (roll_pid < -1 * max_pwm - thrust)
//		roll_pid = -1 * (max_pwm - thrust);
 
	past_error = error;
 
	// compute PWM pulse width
	left_pwm = thrust - (int) roll_pid;
	right_pwm = thrust + (int) roll_pid;
 
	if (left_pwm > 1800)
		left_pwm = 1800;
	else if (left_pwm < 1200)
		left_pwm = 1200;
 
	if (right_pwm > 1800)
		right_pwm = 1800;
	else if (right_pwm < 1200)
		right_pwm = 1200;
 
	/*
	 update duty cycle
	 PA0 - TIM2 CH1 - Left motor
	 PA1 - TIM2 CH2 -Right motor
	 0.02 = PWM frequency | 65535 = ARR value
	 */
	TIM2->CCR1 = (int) (((left_pwm / 1000000) / 0.02) * 65535);
	TIM2->CCR2 = (int) (((right_pwm / 1000000) / 0.02) * 65535);
}

Is there something wrong with this code?

[M7890.1]

The problem happens due to the CCR1 and CCR2 being updated. I did something similar in another code but don't encounter this problem. Why is that so?

[waclawek.jan]

> The problem happens due to the CCR1 and CCR2 being updated.

To what values?

JW

[S.Ma]

Don t do float calculation inside a callback.

[MM..1]

@M7890.1​  Your problem is simple left_pwm uint16 / 1000000 is always 0