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→Asymmetric Multiprocessing
This application note describes in detail the implementation of Linux/FreeRTOS asymmetric multiprocessing configuration on DAVE Embedded Systems AXEL LITE SoM. This configuration is a typical example about how to leverage AMP flexibility to combine, on one single piece of silicon, the versatility of Linux o.s. for general purpose computation, connectivity and HMI and the determinism of an RTOS to satisfy real-time constraints. Since AXEL family products are all based on Freescale i.MX6 processors, what is described here applies to AXEL ULTRA too.
As known, AMP allows a multicore system to run simultaneously[1] multiple Operating Systems (OS) that are independent of each other. In other words, each core has its own private memory space, which contains the OS and the applications that are to run on that core. In addition, there can be some shared memory space that is used for inter-core communication. This is in contrast to Symmetric Multiprocessing (SMP), in which one OS runs on multiple cores using a public shared memory space.
Thanks to AMP, developers can use open-source Linux and FreeRTOS operating systems and the RPMsg Inter Processor Communication (IPC) framework to quickly implement applications that need to deliver deterministic, real-time responsiveness for markets such as automotive, industrial and others with similar requirements, while preserving the openness of Linux.
The following picture depicts the structure of the system.
[[File:XELK-amp-config.png|thumb|center|400px|AMP configuration]]
Core #0:
* takes care of boot process
* once Linux gets control of the processor, initializes core #1 in SMP mode
* stops core #1 and switches it to AMP mode
* loads binary image of FreeRTOS that is then executed by core #1
[1] This is true simultaneity because multiple instructions are executed at the same time.
=== Inter-core communication ===
