TIMER1 compare not triggered for CC=0x00

[Nick]

I am using a TIMER1 compare event to generate an interrupt. Generally the code all works fine, but I have noticed some strange behaviour when loading the CC register with 0x00. If the timer is allowed to run freely and overflow, then it is possible to generate a compare event when the timer rolls-over to 0. No problem there. But then I tried to limit the maximum timer count using;

NRF_TIMER1->SHORTS |= TIMER_SHORTS_COMPARE2_CLEAR_Enabled << TIMER_SHORTS_COMPARE2_CLEAR_Pos;
NRF_TIMER1->CC[2] = T1_TICKS_MAX;

My understanding is that this should cause the timer to reset to zero when it hits the value in CC2 (T1_TICKS_MAX). However, when I do this I no longer get any compare events generated for CC=0x00. Any other CC value less than or equal to T1_TICKS_MAX works fine.

This seems a bit unexpected to me. Is this normal behaviour? Or do I perhaps have a bug in my code somewhere?

[Susheel Nuguru]

I am not sure what you are trying to achive here. Why do you need SHORT to clear timer in this case? What is the value of T1_TICKS_MAX? if it is 0XFFFF Then you do not need that short, it will overflow and the next counter value will be zero anyway.

If you enable clear_short at 0XFFFF, i think the short logic conflicts with the event logic at the same HFCLK cycle and looks like the event is missed. In my opinion, this is expected to be unpredictable in this case.

[Nick]

The value I am currently using for T1_TICKS_MAX is 0x00FE. However, it doesn't seem to matter. The same behaviour occurs for any value of T1_TICKS_MAX.

The reason why I am resetting the count at 0xFE (rather than letting it reach 0xFF and overflow back to zero) is because I want to be able to disable COMPARE events on CC channels. I am disabling COMPARE events by setting the CC register to 0x00FF. Since the timer never reaches this value, a compare event is never generated.

Perhaps there a more sensible way to disable COMPARE events on a single CC channel (without stopping the timer)? I'm open to suggestions.