GPIOTE IRQ loss when too fast....how to use latch?

[lbe]

Hello everyone,

I am working on a project where I need to interface an NFC reader (trf7970a from TI) to an NRF52840.

I got everything working fine, but I have a major issue in reading a tag, essentially because from what I see on the logic analyzer, the NRF52840 "misses" the RX interrupt because it happens too shortly after the TX done interrupt. This is pretty clear from the logic analyzer screenshot below

The IRQ line (blue, channel 14) is well managed when there is only a TX done event (first IRQ), but when a tag is close to the device, it causes a second interrupt that is not managed, most probably because it happen while the NRF is servicing the previous interrupt in nrfx_gpiote_irq_handler function...

I read in some discussion that a LATCH register is available to check if there are pending interrupts, but I was not able to understand how to use it to generate another IRQ....can someone point me to the right direction? Should I poll it periodically, or can I set it somewhere in the gpiote configuration?

Also, is there any way to speed-up the irq management? The two interrupts happen at an interval of 84us, is there a way to speed up the gpiote_irq_handler function to correctly serve the second interrupt?

Thanks a lot!

[Håkon Alseth]

Hi,

 

Are you using nrfx_gpiote or nrf_gpiote? Which SDK are you using?

nrfx_gpiote.c was recently updated with LATCH support:

https://github.com/NordicSemiconductor/nrfx/blob/master/drivers/src/nrfx_gpiote.c#L655

I suspect the easiest way is to update to the latest nrfx version, unless you want to use a GPIOTE IN channel instead (by setting .hi_accuracy = true in your nrf_drv_gpiote_in_config_t my_button variable).

 

This is how you update nrfx to v2.1 in SDK v16:

1. Go to sdk_16\modules and rename "nrfx" to "nrfx_old"

2. Clone the repo (https://github.com/NordicSemiconductor/nrfx) to the same directory

3. The API introduced a interrupt level as an input to nrfx_gpiote_init, where you have to pass a interrupt level (between 0 and 7) to the init, for instance: nrf_drv_gpiote_init(APP_IRQ_PRIORITY_LOWEST);

 

Kind regards,

Håkon

[lbe]

Hello Hakon, thanks for your answer.

I am using nrfx_gpiote and SDK 15.0, but it turned out that the problem I had was not related to the latch but to an error somewhere else in the code (wrong timings).

Thanks in any case for your suggestions.