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]

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.

[Håkon Alseth]

Hi,

Christopher Hunt said:

What I’m actually trying to understand is what peripheral events occur when there is data available so that I should then poll.

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. 

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

[Christopher Hunt]

Håkon Alseth said:

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. 

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

Håkon Alseth said:

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

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.

[Håkon Alseth]

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#

 

Christopher Hunt said:

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.

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

[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.