Asymmetric Multiprocessing (AMP) Intro
An embedded AMP system is characterized by multiple homogeneous and/or heterogeneous processing cores integrated into one System-on-a-Chip (SoC). Examples include:
The AMD Zynq UltraScale+ MPSoCs that utilize four ARM Cortex-A53, two ARM Cortex-R5, and potentially a number of MicroBlaze cores.
The NXP i.MX6SoloX/i.MX7d SoCs that utilize ARM Cortex-A9 and ARM Cortex-M4F cores
The Texas Instruments Sitara AM625 SoCs that utilize ARM Cortex-A53, ARM Cortex-M4F, ARM Cortex-R5F, and PRU-ICSS cores.
The ST STM32MP15x SoCs that utilize ARM Cortex-A7 and ARM Cortex-M4 cores.
These cores typically run independent instances of homogeneous and/or heterogeneous software environments, such as Linux, RTOS, and Bare Metal that work together to achieve the design goals of the end application. While Symmetric Multiprocessing (SMP) operating systems allow load balancing of application workload across homogeneous processors present in such AMP SoCs, asymmetric multiprocessing design paradigms are required to leverage parallelism from the heterogeneous cores present in the system.
Increasingly, today’s multicore applications require heterogeneous processing power. Heterogeneous multicore SoCs often have one or more general purpose CPUs (for example, ARM Cortex-A cores) with DSPs (such as TI C7x cores) and/or smaller CPUs (such as ARM Cortex-M and Cortex-R cores) and/or soft IP (such as AMD MicroBlaze cores). These specialized CPUs, as compared to the general purpose CPUs, are typically dedicated for demand-driven offload of specialized application functionality to achieve maximum system performance. Systems developed using these types of SoCs, characterized by heterogeneity in both hardware and software, are generally termed as AMP systems.
Other reasons to run heterogeneous software environments (e.g. multi-OS) include:
- Needs for multiple environments with different characteristics
Real-time (RTOS) and general purpose (i.e. Linux)
Safe/Secure environment and regular environment
GPL and non-GPL environments
- Integration of code written for multiple environments
Legacy OS and new OS
In AMP systems, it is typical for software running on a host to bring up software/firmware contexts on a remote on a demand-driven basis and communicate with them using IPC mechanisms to offload work during runtime. The participating host and remote processors may be homogeneous or heterogeneous in nature. The remote can also be started automatically, on boot, which may be required where the remote is part of a safety critical system.
A host is defined as the CPU/software that is booted first and is responsible for managing other CPUs and their software contexts present in an AMP system. A remote is defined as the CPU/software context managed by the host software context present.