Architectural considerations Designing and Maintaining a High-Performance Architecture
Well designed software architectures enable better reuse of software components and more rapid development of system variants than monolithic designs.
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Software architectures are necessarily abstractions, and therefore have to be carefully designed to perform well. This case study follows the design of such an architecture for large distributed embedded control systems with lessons on delivering and maintaining system performance as architectures are ported to new platforms.
A software architecture refers to the design of and interactions between software components in a system. An appropriate software architecture will reflect the organizational, technical, and market requirements of the systems it supports . For large distributed embedded systems these requirements typically include being low-overhead, being portable to heterogeneous embedded hardware platforms, and supporting deterministic execution. Designing architectures that support a broad class of applications while retaining these attributes and others is a difficult challenge.
This case study is a research effort within National Instruments to design a software architecture for large distributed embedded control applications. Here we propose an architecture based on modelling data-transfer explicitly as channels, and then separating configuration of the channels from access to channel data. This partitions systems into channel implementations, system composition, and data processing components that can be reused independently within different applications while keeping overhead low.
National Instruments produces software development tools, rather than complete systems. Software development involves realizing a high-level model of an application on a platform . A properly designed software architecture can provide this platform. Our objective was to produce such an architecture by considering the types of embedded applications to target, and what hardware would be required to support them. We considered how those applications would be specified, and derived a software architecture that allowed this while maximizing end user productivity and performance.
The advent of the “internet of things” is driving embedded applications to become larger, more distributed, and more complex. In addition, future applications require heterogeneous hardware for processing and transfer of data. This includes CPUs of varying types, core numbers, and cache hierarchies , FPGAs, GPUs, and bus technologies like PCIe, EtherNET, EtherCat, etc. To this, control applications add a requirement for real-time execution. All of this must be supported efficiently by software development teams with specialized skills sets. This creates a long-term development challenge with consistent requirements that warrants a dedicated software architecture.
To address this, the working group focused on large distributed embedded control applications. The applications were large in terms of the number of IO channels, data-transfer channels and data-processing operations to ensure the architecture could scale appropriately. The applications were distributed, meaning that different data-processing domains were separated by links with high data-transfer latency (high relative to data-processing times).
The applications were also embedded in the sense that the processors and other hardware had to fit into small rugged enclosures that could be integrated into a piece of equipment without impeding its operation. The requirement can be taken to mean that cost, power, and size of the processors and storage must be minimized. Integrating control into these systems requires careful coordination of operations to avoid unpredictable interactions that affect determinism.
The result is a problem space with heterogeneous asynchronously operating data-processing and data-transfer elements that need to be tightly coordinated. The appropriate software architecture must make heterogeneous actors behave consistently and in a coordinated manner without incurring a significant overhead.