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Over the last few years, SoCs targeted at embedded GNU/Linux applications became heterogenous architectures. Instead of adding more identical copies of CPU cores (Cortex-A class), a small companion micro controller core (Cortex-M class) was added. Compared to the complex architecture of Cortex-A systems, including their multi-layer caches, those cores are usually deterministic and thus predestined for low-latency "real time" jobs. NXP's first such SoC is the i.MX6 Solo X device featuring an Cortex-M4 next to an Cortex-A9 core. The i.MX8 family moved the Cortex-A cores into the 64 bit world and there are different combinations of Cortex-M companion micro controllers, but all of them do feature them as they are pretty "cheap" in terms of die space and transistor count.

From what I can see, it is still uncommon to use those micro controllers in actual projects though. Today I want to take a short look on how to run simple programs on the Cortex-M4 of the i.MX8M Mini SoC, especially we will use the official i.MX8M Mini EVK.

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In a recent post, I described the basics to execute code on the Cortex M4 micro controller inside the i.MX8M Mini SoC. However there was no communication going on between Linux on the Cortex A cores and the application running on the M4. In this post, I will look at an example using the remoteproc and rpmsg (Remote Processor Messaging) frameworks for communication between the processors. The remoteproc subsystem implements basic house keeping for co-processors in Linux and the rpmsg framework implements the actual data channels.

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