LPCOMP occasionally missing interrupt

RE: LPCOMP occasionally missing interrupt

Jørgen Holmefjord — Tue, 13 Aug 2019 08:26:23 GMT

I think you will be facing the exact same issue if you switch to GPIOTE, as it seems that the issue is related to handling the interrupt fast enough. There is no operation in the softdevice specifications that should block you from handling the interrupt within the required time, as it seems to be more than 1 ms between the two missed events. Please make sure that you do not run any other peripherals at the same high priority, and that you do not spend excessive time in the interrupt handler.

You can also try with different prescaling/reference and with/without the hysteresis, to see if this makes any difference.

RE: LPCOMP occasionally missing interrupt

Mojo — Mon, 12 Aug 2019 15:53:55 GMT

I am using this library https://github.com/IOsonata/IOsonata/blob/master/ARM/Nordic/src/analog_comp_nrf5x.cpp

It works fine for me.

RE: LPCOMP occasionally missing interrupt

Quantum_Quail — Mon, 12 Aug 2019 14:09:05 GMT

I am using the soft device and I've tried setting the interrupt to priority 2 but the results are still the same. Do you think amplifying the signal and using GPIOTE will result in any differences? Or perhaps there are other libraries I can use?

RE: LPCOMP occasionally missing interrupt

Jørgen Holmefjord — Mon, 12 Aug 2019 14:06:14 GMT

I see. Are you running the LPCOMP interrupt at the highest possible priority? Are you using the softdevice in your application?

RE: LPCOMP occasionally missing interrupt

Quantum_Quail — Mon, 12 Aug 2019 13:58:50 GMT

My original setup is exactly as you have detailed, PPI connecting a TIMER Task out and LPCOMP Event, with an LPCOMP, interrupt attached that collects the CC value. However, since the LPCOMP interrupt misses edges, it throws the entire array of times off. Do you have any suggestions/alternative solutions you could recommend for timing an IR signal?

RE: LPCOMP occasionally missing interrupt

Jørgen Holmefjord — Mon, 12 Aug 2019 11:16:24 GMT

You can use PPI to trigger one of the CAPTURE tasks of the TIMER, which will store the counter value in the corresponding CC register. You will have to read out the CC value in the interrupt, but at least you avoid the delay from event to interrupt is triggered to capture the value. As far as I know, there is no way to store CC value directly into RAM buffer.

RE: LPCOMP occasionally missing interrupt

Quantum_Quail — Fri, 09 Aug 2019 16:06:58 GMT

Hi,

Seems like the problem was that the interrupt to the LPCOMP was being called late. After attaching the GPIOTE to PPI, the signals came out perfect. Since I'm trying to time this IR signal with a hardware timer, is there a way to use PPI to directly store CC values into a buffer instead of using an interrupt as I did before.

RE: LPCOMP occasionally missing interrupt

Jørgen Holmefjord — Fri, 09 Aug 2019 12:44:13 GMT

Hi,

Are you testing this with a minimal example, or does the application perform other tasks as well? If other higher priority tasks are blocking you from clearing the event in the interrupt handler, the event/interrupt may not be generated on the subsequent crossings.

Could you also try to toggle the GPIO using PPI+GPIOTE, to make sure this is only done by this event? You can use this sample code, but connect the EVENTS_CROSS from LPCOMP to PPI EEP, instead of the TIMER event.

Best regards,
Jørgen