What Is Hardware Software Co-design?

Hardware software co-design is a methodology for developing embedded systems in which the hardware platform and the software running on it are designed concurrently rather than sequentially, with each influencing the other throughout the development process. The central goal is to meet system-level objectives for performance, power consumption, cost, and reliability by exploiting the trade-offs available when both domains are treated as jointly optimizable variables. Decisions about which functions belong in dedicated silicon and which in programmable firmware are deferred as long as possible, allowing engineers to redirect effort as constraints become clearer.

The methodology emerged in the early 1990s as embedded systems grew complex enough that a sequential handoff from hardware architects to software developers left too little room for correction. IEEE research on hardware-software codesign of embedded systems established the field's foundational vocabulary, identifying system specification, partitioning, co-synthesis, and co-verification as the four stages of a principled co-design flow.

System Partitioning and Architecture

The partitioning step allocates system functions between hardware accelerators and software running on microprocessors or DSPs, typically with the goal of minimizing cost, area, or execution time subject to real-time constraints. In a co-design flow, both ASIC or FPGA implementations and programmable processor implementations are candidate solutions for every function, and the partition is determined by analysis rather than convention. The hardware-software interface, which defines the registers, interrupts, and memory maps through which the processor communicates with custom logic, is specified formally during this phase so that hardware and software teams can proceed in parallel without waiting for the other side to be complete.

Embedded Software Architecture and Engineering

On the software side, co-design places demands on software architecture that differ from those of general-purpose application development. Embedded software must meet hard real-time deadlines, operate with constrained memory, and rely on hardware abstractions that may change as the hardware partition is revised. Well-structured co-design flows use hardware abstraction layers (HALs) and virtual platform models so that software development can begin before physical silicon is available. Software architecture choices, including task scheduling policies, interrupt service routine design, and communication protocols between cores, feed back into hardware sizing because they determine bus bandwidth and cache requirements. A software/hardware co-design methodology for embedded microprocessor core design describes how tightly coupled hardware and software design loops reduce the number of microarchitectural revisions needed before tapeout.

Co-Verification and Testing

Verification in a co-design context requires that the correctness of hardware-software interactions be checked together, not in isolation. Co-simulation environments couple an RTL or virtual hardware model with a software simulation, allowing test engineers to observe how firmware responds to hardware state and vice versa. Hardware emulation platforms accelerate this step by executing the hardware model at speeds sufficient to boot an operating system or run protocol stacks. Software testing techniques, including unit tests, integration tests, and model-in-the-loop validation, are applied earlier and against more complete system models than in traditional flows. Software reliability and the dependability of timing-critical paths are both assessed within the co-verification stage. Work on synchronous methodology for hardware, software, and mixed embedded systems design presents a unified specification framework that makes co-verification tractable for control-dominated applications.

Applications

Hardware software co-design has applications in a wide range of fields, including:

• Automotive electronic control units (ECUs) for powertrain, chassis, and advanced driver assistance systems
• Industrial programmable logic controllers and real-time automation platforms
• Consumer electronics SoCs combining application processors with custom media and connectivity accelerators
• Medical devices requiring certified software operating on custom hardware pipelines
• Telecommunications infrastructure processing high-bandwidth data with a mix of DSP cores and custom logic