How to become notified of BSD non-blocking events

[Christopher Hunt]

Hi there,

I'm intending to use the nrfxlib modem library and its BSD socket implementation on the nRF9160. My goal is to use non-blocking APIs and use `nrf_poll` in response to various events.

For example, I'd like to use `nrf_recv` (1) with `NRF_O_NONBLOCK` and then receive a notification when there is data available given its respective file descriptor. To achieve this, I'm wondering if I can connect an IPC RECEIVE event with all IPC channels, which'd see that `nrf_poll` is then called by my code.

Thanks for any guidance here.

(1) https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/api.html#group__nrf__socket__api_1ga1a288076f560857cb46fa0df46e1c7e5

[Håkon Alseth]

Hi,

 

I'm intending to use the nrfxlib modem library and its BSD socket implementation on the nRF9160. My goal is to use non-blocking APIs and use `nrf_poll` in response to various events.

For example, I'd like to use `nrf_recv` (1) with `NRF_O_NONBLOCK` and then receive a notification when there is data available given its respective file descriptor. To achieve this, I'm wondering if I can connect an IPC RECEIVE event with all IPC channels, which'd see that `nrf_poll` is then called by my code.

You can use poll() for this use case, and then check the revents if there's data available for you. mqtt and coap samples sets this up in the main loop:

https://github.com/nrfconnect/sdk-nrf/blob/v1.8.0-rc2/samples/nrf9160/coap_client/src/main.c#L246-L274

https://github.com/nrfconnect/sdk-nrf/blob/v1.8.0-rc2/samples/nrf9160/mqtt_simple/src/main.c#L600

 

Kind regards,

Håkon

[Christopher Hunt]

Håkon Alseth said:

You're halfway right in the understanding of the function, its main purpose is to sleep for a timeout-period or until something happens on that specific socket. Think of it as an event based system.

My app has other peripherals to service and not just the modem and so I can't block on the latter. I was looking for an interrupt or event that I can hook onto indicating that "something" has happened re. the modem worthy of a subsequent call to nrf_poll. I'm unsure how `nrf_modem_os_timedwait` achieves this as it must be something called indirectly from the main loop of my program. I suspect that subscribing to the IPC events might be sufficient. Thanks for any confirmation and apologies if I'm still not yet understanding something.

[Håkon Alseth]

Hi,

 

Christopher Hunt said:

My app has other peripherals to service and not just the modem and so I can't block on the latter. I was looking for an interrupt or event that I can hook onto indicating that "something" has happened re. the modem worthy of a subsequent call to nrf_poll. I'm unsure how `nrf_modem_os_timedwait` achieves this as it must be something called indirectly from the main loop of my program. I suspect that subscribing to the IPC events might be sufficient. Thanks for any confirmation and apologies if I'm still not yet understanding something.

You are free to implement the nrf_modem_os_timedwait() in any way you'd like, including wrapping it around your applications sleep/event based system.

 

This is the interrupt that wakes up the threads if anything has happened:

https://github.com/nrfconnect/sdk-nrf/blob/v1.7.1/lib/nrf_modem_lib/nrf_modem_os.c#L437-L453

 

here is a reference/template implementation of the file for porting into other systems:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/ug_nrf_modem_porting_os.html#reference-template-for-the-nrf-modem-os-c-file

 

Kind regards,

Håkon

[Christopher Hunt]

Håkon Alseth said:

This is the interrupt that wakes up the threads if anything has happened:

https://github.com/nrfconnect/sdk-nrf/blob/v1.7.1/lib/nrf_modem_lib/nrf_modem_os.c#L437-L453

 

Ah ha - so following that lead, I discover this in the nrf_modem_platform.h file:

/**@brief Interrupt used for communication with the application layer. */
#define NRF_MODEM_APPLICATION_IRQ EGU1_IRQn

...so I should be able to subscribe to trigger events on EGU1 and then ultimately call nrf_poll as a consequence.

Please let me know if I'm on track, and again thanks for your help so far.

[Håkon Alseth]

Hi,

 

It is not that simple, unfortunately, as this event is used for all events coming from the modem. See the message sequences here for more details:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/ug_nrf_modem_porting_os.html#id4

I am unable to give a definite answer on your scenario in question, as its not a scenario that we've tested directly. What you're suggesting might work for a single-socket application, but I fear is problematic for multiple sockets scenario.

 

Which platform/language are you porting to?

 

Kind regards,

Håkon

[Christopher Hunt]

Håkon Alseth said:

It is not that simple, unfortunately, as this event is used for all events coming from the modem. See the message sequences here for more details:

I'm ok with that though... I'm just looking for an event that provides a reasonable excuse to call nrf_poll with a 0 timeout to find out about what, if anything, happened.

Håkon Alseth said:

I am unable to give a definite answer on your scenario in question, as its not a scenario that we've tested directly. What you're suggesting might work for a single-socket application, but I fear is problematic for multiple sockets scenario.

nrf_poll should work for multiple sockets though...

Håkon Alseth said:

Which platform/language are you porting to?

This is for use from the https://github.com/embassy-rs/embassy framework using Rust.

Further to my questions here, is there any possibility that Nordic could open source the modem library and document the hardware interface of the modem? Thanks again.

[Håkon Alseth]

Hi,

 

Christopher Hunt said:

nrf_poll should work for multiple sockets though...

Yes, but if you have multiple poll() functions across different modules, it might be problematic.

Christopher Hunt said:

This is for use from the https://github.com/embassy-rs/embassy framework using Rust.

Further to my questions here, is there any possibility that Nordic could open source the modem library and document the hardware interface of the modem? Thanks again.

It is closed source, atleast for the time being. I'll input this internally as a feature request.

 

Kind regards,

Håkon