how to subtract specific value from counter pulses in each instance in stm32

[Tashenlrana]

I am using stm32G431C8U6 microcontroller and I use TB6612 motor driver to control two motors with encoders. I have enabled timer 2 channel 3 and 4 for PWM generation and Timer3 and Timer 4 for combined channel encoder mode. Also I have used Timer15 for timer interrupt. I need to move the two motors for a specific counter pulses (eg:25,000) and then I need to stop them when timer3 counter reaches to specified counter pulses. In the code it will not exactly stop at 25,000(specified counter pulses) and it will deviated  more than 25,000 (like 25,123,25,200) .Hence I have used PID function to mitigate this issue. I have enabled timer 15 for interrupt and in that interrupt function I have called back my PID function.

In the PID function it is supposed to be that counter starts from 0 and every 100ms it will increment by one. For an example initially timer 3 counter at 0 and then next 100ms it will reach to one. Then I have designed the pid function as below,

apply_pid(int error)

{

int Kp=0.01;

int16_t output =0;

error = 25,000 - CounterTicks;

output = (Kp)*error;

TIM2->CCR3 == output;

 

}

 

In here CounterTicks is the variable for counterpulses. Here I have used only proportional part for simplicity.

According to theory that interrupt function will callback the PID function and there

counterticks will increment by instance of every 100ms and each instance it will calculate error and assign that value to PWM CCR variable.Then error will be proportional to pwm and eventually motors should stop intended counterpulses which is 25,000.

The issue is code does not work as intended. Hence I need your help to configure this issue. Thank you.

 

 

 

 

[STuser2]

I don't understand the complete code but one mistake i could see is

TIM2->CCR3 == output;

you have used "==" instead of "="

[Tashenlrana]

Here is the complete PID function that I have written

 

apply_pid(int error)

{

int8_t MSG[20] = {'\0'};

int8_t PID[20] = {'\0'};

int8_t OPT[20] = {'\0'};

int16_t CounterTicks = 0;

int16_t out_pid = 0;

int16_t output =0;

 

int Kp =0.01;

 

error = 25,000 - CounterTicks;

output = (Kp)*error;

TIM2->CCR3 = output;

 

if (error = 0)//Stop

{

 

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_5,0);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_4,0);

HAL_GPIO_WritePin(GPIOC,GPIO_PIN_4,1);

HAL_GPIO_WritePin(GPIOA,GPIO_PIN_7,1);

 

}

else if(error < 0)//rotate reverse

{

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_10,0);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_11,1);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_0,0);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_1,1);

TIM2->CCR3 = output;

TIM2->CCR4 = output;

}

else //rotate forward

{

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_10,1);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_11,0);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_0,1);

HAL_GPIO_WritePin(GPIOB,GPIO_PIN_1,0);

TIM2->CCR3 = output;

TIM2->CCR4 = output;

 

if(output >= 499)

{

TIM2->CCR3 =499;

}

else

{

TIM2->CCR3 = output;

}

 

}

return error;

}

I still could not find out how to substarct each counter pulses in each instance from 25,000(specified counter pulse) to get error. Counterticks value and Current PWM value(out_pid) will be transmitted to serial monitor as UART signal in main function.

 

[STuser2]

if (error = 0)//Stop

i suggest you use some static analyzer tool.

[mfgkw]

I don't understand either your plans.

But when I see this:

error = 25,000 - CounterTicks;

I get in troubles.

Is 25,000 supposed to be a floating point const?

 

A C compiler will interpret this as a comma operator. So error gets the value 25, then 000-CounterTick will be calculated and the result is dropped.

[Tashenlrana]

Yeah that is one issue that I have done. Hence it should be

error = 25000 - Counterticks;

Thank you.

[TDK]

> int16_t CounterTicks = 0;

> int16_t out_pid = 0;

> int16_t output =0;

 

> int Kp =0.01;

 

> error = 25,000 - CounterTicks;

> output = (Kp)*error;

> TIM2->CCR3 = output;

 

Doesn't this just set CCR3 to 250 all the time? Is that useful?

 

You can change the counter value by writing to CNT directly.

[Tashenlrana]

Technically when motor get rotated CounterTicks will be increased then error value should be decreased. As a result output should be reduced starting from 250 untill 0. Code does not working as intended because once code is compiled motors did not initiate it's rotation. Hence I get Counterticks = 0 whenever I run the code.