STM32F7 Timer Event Generation Register Wrong address?

[mcu person]

Hello I'm using a STM32F769 discovery board. I was trying to use timer2channel2 to trigger the ADC conversion. I am setting registers manually and wanted to turn on event generation on channel 2 match.

TIM2->EGR |= TIM_EGR_CC2G_Msk;

However when I ran the code it didn't work. I opened the debugger and discovered when I run that particular line of Code it is actually setting the same bit in the status register (TIm2->SR) has anyone else seen this problem? Is there any work around, or am I just missing something

heres my code for reference

void init_timer2(void)
{
    //1. Clock
    RCC->APB1ENR |= RCC_APB1ENR_TIM2EN_Msk;
    
    TIM2->PSC = 1600 -1;
    TIM2->ARR = 10000;
    TIM2->CNT = 0;
    TIM2->CCR2 = 1000;
    
    //now set up trigger, we are basically using compare mode
    TIM2->EGR |= TIM_EGR_CC2G_Msk
              |  TIM_EGR_UG_Msk; //this doesn't work whenever you write to EGR it goes to SR register
                
    TIM2->CCMR1 |= (0x01 << TIM_CCMR1_OC2M_Pos)//sets pin high on compare match
                |  (0x01 << TIM_CCMR1_OC2PE_Pos);//enable preload register?
    
    TIM2->CCER |= TIM_CCER_CC2E_Msk;
    
    //start timer
    TIM2->CR1 |= TIM_CR1_CEN_Msk;
}

[waclawek.jan]

I don't quite understand what do you want to accomplish.

Setting bits in EGR register causes the respective internal signal to get active; one of the consequence of which is that respective SR bit gets set. Btw. you don't need to RMW the EGR register, simply write to it if you need to - which I doubt you need. Although you may want to set EGR.UG, as that's the way how the value you wrote into PSC gets used immediately after the timer starts - otherwise the first timer period would run at the reset setting of PSC=0.

Setting CCMRx.OCxM to 0b001 i.e. active-on-match means, that at the first time CNT matches CCRx, the respective output gets active and then it remains so indefinitely. It's maybe not what you want; you probably want one of the PWM modes.

Re-read the timer chapter. I know it's not written very comprehensibly but after several readings and several experiments things usually start to make sense.

JW

[mcu person]

Hey JW,

Thanks for your response, it clears up a lot. From the reference manual I was thinking mode 0001 "set active on match" would generate a pulse, not a one time state change. I've switched to PWM mode and I'm getting periodic behavior like I wanted.

As for the EGR, I was thinking it enabled flag generation. I used to do a lot of atmel programming, where you have to set bits to enable flags/interrupts, so I thought that this was the same. I guess the flag is always generated as long as the timer is on. Now I see the EGR is for immediate one time flag generation.

Thanks again, I really appreciate it.