Multiple IPC channels

[Robert de Brum]

Hello,

Referencing this link here, I am looking for any updates to using IPC for some custom inter-core communication WHILE ALSO running Bluetooth on an nrf5340.

Long story short, I have a project with custom code for both the cpu_app and cpu_net cores of an nrf5340, and I am looking for a way to communicate between both. Right now, the cpu_net code is running the hci_rpmsg sample so that I can use BLE from the application core. I have not found a clean way to modify this to provide some hooks for my custom use case, nor do I want to try.

If there are any updates on being able to use a custom IPC channel and BLE at the same time, or if IPC is not the right abstraction layer to go through, please let me know! The link I provided mention using the BTS but I am not sure how that is relevant or possible.

I know that there are some complex structures being put to use here and I have tried to spend some time learning it but perhaps there is an easy-to-follow overview of inter-process communication that shows us how IPC, RMPSG, ICMSG, MBOX, shared SRAM and all other abstraction layers play together.

Thank you much.

[Sigurd]

Hi!

The right abstraction layer will depend on what you want to send / communicate between the core. 

If you want to e.g. call a function to run on the net core, from the app core, then maybe Remote procedure call library is the way to go. You can see how that's used in e.g. this sample: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/samples/nrf_rpc/entropy_nrf53/README.html

[Robert de Brum]

What if I want an event that can be heard between cores?

For example, if I am using the time sync sample to synchronize a clock on the network core, can I have the the application core subscribe to tick events from that timer? I know that the timer peripherals for both cores are treated separately, so if this is not possible, are there any sort of events I can trigger that will signal between the cores?

The ultimate goal is to have a system that runs in the background that:

• synchronizes a clock
• takes ADC readings on tick events of that clock
• notifies the foreground code when a buffer of ADC samples is complete
• repeats this cycle

We managed to complete this in the nrf5 SDK on the 52832 but need it now on the 5340 with NCS. If there is a way you can imagine sharing events between core's or even signaling to each core in the background that would be great.

I will play around with this remote procedure library.

Thanks

[Sigurd]

Hi!

For the use-case you describe here, I think it would make more sense to use IPC more directly. Take a look at this example code found in this post:

 RE: [NCS2.2.0] APP Core is time-synchronized with NET Core timer. 

[Robert de Brum]

Thank you for this, this is helpful, as is the nrf53_sync_rtc sample. However I am trying out some things from these and I still run into the issue of BLE competing with the IPC calls.

I added this code to my cpu_app code (from the nrf53_sync_rtc sample) to try and send a message to the network core. I get the following message:

nrf_ipc_task_t task = offsetof(NRF_IPC_Type, TASKS_SEND[2]);
uint32_t shared_cell = 0x20070000;

*(volatile uint32_t *)shared_cell = 0xDEADBEEF;
nrf_ipc_task_trigger(NRF_IPC, task);

[Robert de Brum]

I should mention that this works sometimes, other times it seems to time out.

[Sigurd]

The hci_rpmsg uses some IPC channels.

If you are using e.g. channel 0, then try using a different one, e.g. 5 , and see if that improves anything.

[Robert de Brum]

Sigurd,

That makes sense, but I just tried a few different channels (channel 2, 5, and 15) and they all did not work. I tried to inspect the peripherals at a breakpoint to see which are being used but I was unable to figure it out. How can I tell which ones are being used by HCI?

What else can I look for to prevent this issue? I used the code from the nrf53_sync_rtc sample - is there an example of this merged with a BLE sample?

Thanks.

[Sigurd]

Hi!

Robert de Brum said:

but I just tried a few different channels (channel 2, 5, and 15)

Did you do it on both cores? If yes, then I will try to reproduce and debug this.

Robert de Brum said:

How can I tell which ones are being used by HCI?

I tried just reading out the IPC registers, looks like channel 0 and 1 was used.