By Adam Taylor

As we are going to be looking at both the Zynq Z-7000 SoC and the Zynq UltraScale+ MPSoC in this series moving forward, one important aspect we need to consider is how we can best leverage the processor cores provided within our chosen device. How we use these cores of course, depends upon the system architecture we implement to achieve the overall system requirements. Increasingly, system designers use an asymmetric approach to obtain optimal performance and to address the system-design challenges. Of course, system-design challenges are usually application-specific.

At this point, those unfamiliar with the term may find themselves asking what an asymmetric approach is? Simply put, a asymmetric approach is one where different processing elements within a device perform different functions and indeed some may be running different operating systems to achieve that function. One example of this would be one of the two ARM Cortex-A9 processor cores of a Zynq SoC running Linux and handling system communications and other tasks, which do not need to be addressed in real time, while the second processor core runs a bare-metal application or a FreeRTOS application to execute real-time processing tasks and communicating results to the other core.

When we implement systems in such a manner, we call this asymmetric multi-processing or AMP. We have looked at AMP before, briefly. However, we did not look at the OpenAMP framework developed by the Multicore Association. This open-source framework is supported by both the Zynq SoC and Zynq UltraScale+ MPSoC and provides the software elements necessary for us to establish an AMP system. As such, it is something we need to be familiar with as we develop our examples going forward.

The alternative is a symmetric multi-processing (SMP) system in which all the cores run the same operating system and are balancing the workload among themselves. An example of this would be running Linux on both cores of a Zynq SoC.

Creating an AMP system allows us to leverage the parallelism provided by having several processing cores available, i.e. we can set different cores to perform different tasks under the control of a master core. However, AMP does come with challenges such as how inter-process communication is implemented, how resources are shared, process control, and how the life cycle is managed. The OpenAMP framework is designed to address these issues and to enable reuse and portability at the same time.

When working with the Zynq SoC and Zynq UltraScale+ MPSoC, we can implement AMP solutions which have the following configuration:

Linux Master – Bare-Metal remote

Linux Master – FreeRTOS remote

I should note at this point that while in the Zynq SoC, we can use one core to run Linux as the master, in the Zynq UltraScale+ MPSoC we can use the quad-core APU (based on ARM Cortex-A53 processorsto run Linux while using the dual-core RPU (based on ARM Cortex-R5 processors) as the remote to run the bare-metal or FreeRTOS applications.

The master core, running Linux contains most of the OpenAMP framework within the kernel. There are main three components:

virtIO – Virtualization, which allows communication with the network and device drivers

remoteProc – This is the API that controls the remote processor. It starts and stops the execution, allocates resources, and creates the virtIO devices. This API performs what is often termed the Life Cycle Management (LCM) of the remote processor

RPMesg – The API that allows inter-process communication between the master and remote processors.

The diagram below (taken from UG1186, “OpenAMP Framework for Zynq Devices”) illustrates the process between master and remote processor using OpenAMP.

Example of OpenAMP flow

Of course, when we build our bare-metal and FreeRTOS applications, we also need to include the necessary libraries within the BSP to enable these to support OpenAMP. The libraries we need to enable are the OpenAMP library and the libmetal library.

Having introduced the OpenAMP concept, next week we will look at how we can get an example up and running on a Zynq device.

Code is available on Github as always.

If you want E book or hardback versions of previous MicroZed chronicle blogs, you can get them below.

First Year E Book here

First Year Hardback here

Second Year E Book here

Second Year Hardback here

All of Adam Taylor’s MicroZed Chronicles are cataloged here.