How to become notified of BSD non-blocking events

RE: How to become notified of BSD non-blocking events

Christopher Hunt — Thu, 09 Dec 2021 22:39:01 GMT

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342781#342781"]

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

[/quote]

That would be greatly appreciated. Please let me know if there is anything I can do to help support such an initiative.

RE: How to become notified of BSD non-blocking events

Håkon Alseth — Thu, 09 Dec 2021 17:00:13 GMT

Hi,

[quote user="Christopher Hunt"]nrf_poll should work for multiple sockets though...[/quote]

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

[quote user="Christopher Hunt"]

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.

[/quote]

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

Kind regards,

Håkon

RE: How to become notified of BSD non-blocking events

Christopher Hunt — Thu, 09 Dec 2021 01:23:44 GMT

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342510#342510"]

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:

[/quote]

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.

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342510#342510"]

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.

[/quote]

nrf_poll should work for multiple sockets though...

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342510#342510"]

Which platform/language are you porting to?

[/quote]

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.

RE: How to become notified of BSD non-blocking events

Håkon Alseth — Wed, 08 Dec 2021 10:22:06 GMT

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

Which platform/language are you porting to?

Kind regards,

Håkon

RE: How to become notified of BSD non-blocking events

Christopher Hunt — Wed, 08 Dec 2021 10:02:27 GMT

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342484#342484"]

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

[/quote]

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.

RE: How to become notified of BSD non-blocking events

Håkon Alseth — Wed, 08 Dec 2021 08:58:06 GMT

Hi,

[quote user="Christopher Hunt"]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.[/quote]

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

RE: How to become notified of BSD non-blocking events

Christopher Hunt — Tue, 07 Dec 2021 22:36:10 GMT

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342263#342263"]

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.

[/quote]

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.

RE: How to become notified of BSD non-blocking events

Håkon Alseth — Tue, 07 Dec 2021 09:01:28 GMT

Hi,

Have you looked at this page in the docs?

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

[quote user="Christopher Hunt"]However, it appears that the purpose of this callback is to sleep. I don't want to do that. :-) I want my program to call poll if it is likely that there has been some socket activity. Apologies if I'm being unclear. I appreciate your replies.[/quote]

No apologies necessary, I'm equal to blame for misunderstanding!

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.

The specific function takes a semaphore/mutex, with a timeout provided by the socket call, and if an event occurs before the timeout, it will give the sem/mutex and return an event to the application.

Kind regards,

Håkon

RE: How to become notified of BSD non-blocking events

Christopher Hunt — Tue, 07 Dec 2021 08:07:36 GMT

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342240#342240"]

Triggering of a hw event indicates that something has happened, it does not indicate what. This comes by parsing the data, which is done in the "libmodem", which then exposes a given API towards your application.

[/quote]

Yes, understood. I'm happy to call poll often even if the peripheral event is only a hint toward poll needing to be called.

[quote userid="2115" url="~/f/nordic-q-a/82412/how-to-become-notified-of-bsd-non-blocking-events/342240#342240"]

This is the callback that is triggered when one (or more) events have occurred on a socket:

[/quote]

I should explain that I'm not using Zephyr. However, it appears that the purpose of this callback is to sleep. I don't want to do that. :-) I want my program to call poll if it is likely that there has been some socket activity. Apologies if I'm being unclear. I appreciate your replies.

RE: How to become notified of BSD non-blocking events

Håkon Alseth — Tue, 07 Dec 2021 07:47:16 GMT

Hi,

[quote user="Christopher Hunt"]What I’m actually trying to understand is what peripheral events occur when there is data available so that I should then poll.[/quote]

This is the callback that is triggered when one (or more) events have occurred on a socket:

https://github.com/nrfconnect/sdk-nrf/blob/v1.7.1/lib/nrf_modem_lib/nrf_modem_os.c#L198

Which then tells the socket operation, poll() for instance, that a event is returned.

Kind regards,

Håkon

RE: How to become notified of BSD non-blocking events

Christopher Hunt — Mon, 06 Dec 2021 18:27:39 GMT

Thanks for the reply. What I’m actually trying to understand is what peripheral events occur when there is data available so that I should then poll. I’m wondering if connecting the IPC RECEIVE event is sufficient.

RE: How to become notified of BSD non-blocking events

Håkon Alseth — Mon, 06 Dec 2021 09:09:19 GMT

Hi,

[quote user=""]

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.

[/quote]

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