Wakeup GPIO configuration in Serial LTE Modem

[Nikint]

Hello,

We are working on a project having nRF9160 and STM32 microcontroller. We are using Serial LTE Modem firmware application for nRF9160.

We have gone through below link to configure wakeup pin related configuration -

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/applications/serial_lte_modem/doc/slm_description.html

We want to use P0.17 pin for cellular modem to wakeup from sleep. We had configured UART2 for AT command transactions.

Our queries are as follows -

1. Can we configure P0.17 pin as wakeup just adding "CONFIG_SLM_WAKEUP_PIN = 17" ?

2. Is there any dependency of UART on wakeup pins as we are using UART2 ? 

3. Also, we want to wakeup another MCU when eDRX mode is used, so modifying "CONFIG_SLM_INDICATE_PIN = 18" will configure wakeup output?

Your quick response appreciated.

Thank you.

[Nikint]

Hi Hakon,

Adding more queries in same thread.

We had gone through Serial LTE modem documentation. We understand that, cellular modem's wakeup logic is active LOW. 

So, we want to know, minimum duration of pulse required to acknowledge the wakeup event in cellular modem.

Thank you.

[Hakon]

This is a question to our GPIOTE IP. GPIOTE is timed with 16MHz, so a cycle is 62.5ns. SLM used level (GPIOTE_PORT) interrupt for low power, the minimal time required should be longer than one cycle, for example 100ns~. If you remember the app_uart in legacy SDK, the default triggering time is 100ns. NOTE for edge interrupt (GPIOTE_IN), the input signal should be <= 8MHz.

What's more, if SLM has the PIND_IND defined, there is a hardware handshake mechanism, that when the PIN_WAKEUP has waken up SLM, it will in turn assert PIN_IND to indicate that it's ready. With this there is no need of timer control on MCU side for asserting PIN_WAKEUP.