[roivai]

Actually STM32F1xx has only 16-bit timers. But there is quite easy way to overcome that limitation. I have done it like this:

void getCount()
{
int16_t now = TIM3->CNT;
int16_t delta = now - oldcount;
oldcount = now; //oldcount is volatile int16_t global variable
count += delta; //count is volatile int32_t global variable
}

As you can see, here a difference between current value and the previous value is calculated and this is added to the 32-bit count-variable. Now you only have to make sure that the getCount function is called often enough that the actual 16-bit counter doesn't go more than 32k (15bit) steps between calls. So basically you call it in your PID loop and it works fine.

Pekka

[mcm_xyz]

Actually STM32F1xx has only 16-bit timers. But there is quite easy way to overcome that limitation. I have done it like this:

void getCount()
{
int16_t now = TIM3->CNT;
int16_t delta = now - oldcount;
oldcount = now; //oldcount is volatile int16_t global variable
count += delta; //count is volatile int32_t global variable
}

As you can see, here a difference between current value and the previous value is calculated and this is added to the 32-bit count-variable. Now you only have to make sure that the getCount function is called often enough that the actual 16-bit counter doesn't go more than 32k (15bit) steps between calls. So basically you call it in your PID loop and it works fine.

Pekka

Thanks for the suggestion! I think I will do it like this... In my latest tests with mikropascal I obtained with STM32F407 almost 200kHz for PID frequency... so it's damn fast... so I am pretty sure that it can make some additional calculations and still keep up the high frequency... and there is no interupt like this to disturb the mcu. After some tests I intend to move the PID update on a timer so it will execute at constant intervals... I guess 50KHz or even lower is enough...

Thanks again!

Mihai