LPUART nRF9160 - nRF52840

[Michal Mühlpachr]

Related to https://devzone.nordicsemi.com/f/nordic-q-a/76545/lpuart-nrf9160---nrf52840 (I can not add reply there).

With ncs v1.6.0 every second AT transaction fails.

We appreciate the addition of the native support for LPUART in SLM (without need to modify sources - just using prj.conf option). We discuss it with a sales representative/support also.

We believe bringing LPUART to the SLM application requires a more extensive understanding of lower-level mechanisms rather than just enabling some Kconfig options, some source patches for binding and recompilation and we think in the future, it could be really important for other customers also.

Why? Let's say the customer wants to use NB-IoT eDRX feature and receive notification from the modem when the datagram from network is available. At the same time, you don't want to keep UARTs on both MCUs running (mainly because high speed clock power consumption), and Nordic's LPUART is a perfect solution for such a situation.

Thank you.

[Albrecht Markus Schellenberger]

Hello Michal,

Michal Mühlpachr said:

What do you think about LPUART native support in SLM ?

I’m not sure if this is the intention of the Serial LTE modem application. As described in the application guideline, "The Serial LTE Modem (SLM) application demonstrates how to use the nRF9160 as a stand-alone LTE modem that can be controlled by AT commands." Hence, its purpose is not to demonstrate energy efficiency. If that is the main focus, you probably wouldn’t use the nRF9160 as a stand-alone modem only. But anyway, the LP UART is of course supposed to work regardless application.

I haven’t tested this myself yet, but what you could try in the meantime is to disable Zero-latency interrupt extension by setting:

CONFIG_ZERO_LATENCY_IRQS=n

in your prj.conf. This should give better performance to the module.

Regards,

Markus

[Michal Mühlpachr]

SML has #XSLEEP who cares of various sleep modes, LPUART would be nice to handle clock/UART sleeping in automated way. We use BLE in our device, so we need additional nRF52840 where whole application logic is implemented and nRF9160 servers just as modem. Because nRF9160 in sleep mode draws just around 7uA with SLM it is still more then appropriate for low power battery operated device.

CONFIG_ZERO_LATENCY_IRQS=n is default for SLM