Help with custom OpenThread simulation

[MichaelFeistETC]

I'm trying to set up my project so that I can build OpenThread to either run on hardware or run in a simulator on a Linux PC using the same application code. The project uses Zephyr. I'm having trouble getting things to link properly. (I can't use babblesim since some of my devices won't be running Zephyr)

Zephyr's networking stack looks like this (when using Openthread):

Zephyr networking stack
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OpenThread networking stack
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Zephyr platform shim/drivers

I know OpenThread provides simulation on posix targets. From my understanding that looks like this:

OpenThread networking stack
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OpenThread Posix platform shim/drivers

That makes me think it should be possible to do the following since Zephyr supports a native_sim target that runs on posix platforms:

Zephyr networking stack
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OpenThread networking stack
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OpenThread Posix platform shim/drivers

One of my biggest problems right now is I can't seem to figure out what targets I need to link against in order to get that OpenThread Posix platform shim/drivers layer. I'm currently trying to link against openthread-ftd and openthread-simulation, but I'm going wrong somewhere. Zephyr can't find <openthread-system.h>. If anyone can tell me whether this approach is just dumb or what I'm doing wrong, it would be greatly appreciated.

[abtink]

I can try to provide some inputs that I hope may help you.

OpenThread defines a set of platform APIs (otPlat) that the platform layer must provide. This includes alarms (timers), tasklets, radio, settings, logging, etc. These are all defined in the include/openthread/platform/*.h headers.

When integrated into Zephyr, all OT platform APIs are provided by the OS (Zephyr).

OpenThread itself provides a "simulation platform" example that implements all of the platform APIs. This is located under example/splatform/simulation and can be enabled by the CMake option OT_PLATFORM=simulation.

If you want to run simulations under Zephyr, I expect certain OT platform APIs to still be provided/emulated by Zephyr. For example, alarms (timers) and tasklets are tied to the OS and it makes sense for them to be part of Zephyr. However, you may want to emulate otPlatRadio APIs instead.

So, the way I would go about this is to expand the Zephyr platform shim/drivers to include emulation of OT platform APIs. These can be similar to what the OpenThread "simulation platform" example does.

[MichaelFeistETC]

After looking a bit further, it looks like I might just need to implement a simulation IEEE 802.15.4 driver in Zephyr. i.e. Just use posix APIs to do UDP multicast between nodes and pretend to be an IEEE radio. Zephyr doesn't have its platform code split up as nicely as I'd like in order to be able to stitch this all together by only messing with the build system. It looks like this would mean I'd have to do a similar round of work to implement the same backend for OpenThread via the platform API (for non-zephyr targets). Although, I likely can rip a decent chunk of the work from existing platform examples. Thank you for the input @abtink!