How to get GPIO register state in GPIOTE handler

[Vas]

Hello Nordic! My question probably a simple one but I'm a novice so there's it. I'm looking for a way to get a GPIO port state that was at the moment of GPIOTE event triggering, inside the event handler. Is there any register I can read to get that?

The context: I'm trying to read a two line serial bus of TitanMicro TM1640. The start of transmission is designated by falling DIN line while SCLK line is still high. The time between falling DIN and falling SCLK is about 10 us, so when I'm reading the GPIO from the handler the SCLK is already low.

[Sigurd]

Hi!

A GPIOTE event can come from one of the following input conditions:

• Rising edge
• Falling edge
• Any change

So if you have e.g. configured it to Rising edge, you then already know it was rising to high when the event triggered.

[Vas]

I'm actually looking at the other signal state. I'm catching DIN change by GPIOTE but I need to know if SCLK was high at the moment.

[Sigurd]

Vas said:

I'm catching DIN change by GPIOTE but I need to know if SCLK was high at the moment.

If this SCLK is a input, you could try reading the GPIO IN register. https://docs.nordicsemi.com/bundle/ps_nrf52840/page/gpio.html#ariaid-title7

[Vas]

Will I get the input state of the moment when the GPIOTE event triggered or I'll get the current reading?

[Sigurd]

Current reading. I'm not familiar with TM1640. Is the SCLK input or output from the nRF52840 ?

[Vas]

Both DIN and SCLK are inputs for the nRF52840 in my case. And if that would be the current reading it will be the issue I described in the original post. The time difference between falling DIN and SCLK is 10 us so when I'm reading the GPIO input from the handler it's already past that time and the SCLK is already fallen low.

[Sigurd]

Hi,

Unfortunately, it is not possible to capture digital levels on GPIOs using PPI.

Some potential workarounds:

1) You can configure the GPIOTE to generate an event on GPIO rising edge, falling edge or any change for the SCLK input.
You can then configure a TIMER instance in counter mode, and use it to keep track of how many times the GPIOTE event has been generated.
If you know the initial gpio state(high/low), then you also know the current GPIO state simply by looking at the counter value.
Trigger the TIMER CC capture task using PPI with the GPIOTE event for the DIN. Then in the GPIO handler, you can read TIMER CC register, and based on that value you can know if the SCLK was high or low.

2) Use SAADC, see this post:  RE: Is it possible to read a data pin with PPI? (PS/2 bit banging using PPI) 

[Vas]

Thank you for the links. I got another idea - what if I connect both DIN and SCLK to an AND logical element and feed the result to another GPIO pin. Both signals never change together. Will I be able to check which GPIOs were triggered in GPIOTE event handler?

[Sigurd]

Hi, yes, that could work. You will get the pin number in the gpiote handler.