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Embedded computers are ubiquitous in products across various industries, including the automotive and medical industries, and in consumer goods such as appliances and entertainment devices. These specialized computing systems utilize Systems on Chips (SoCs), devices that are made up of one or more main microprocessor cores. SoCs are augmented with sub-blocks that perform dedicated tasks to support the system. Sub-blocks contain custom logic or small-footprint microprocessors, depending upon their complexity, and perform support functions such as clock generation, device testing, phase-locked loop synchronization and peripheral management for interfaces such as a Universal Serial Bus (USB) or Serial Peripheral Interface (SPI). SoC designers have traditionally obtained sub-blocks from commercial vendors. While these sub-blocks have well-defined interfaces, their internal implementations are opaque. Without visibility of the specifics of the implementation, SoC designers are limited to the degree to which they can optimize these off-the-shelf sub-blocks. The result is that power and area constraints are dictated by the design of a third-party vendor. This work introduces a novel idea: using an open-source, small, multitasking, real-time operating system inside an SoC sub-block to manage multiple processes, thereby conserving code space. This OS is TurbOS, a new operating system whose primary goal is to provide the highest performance using the least amount of space. It is written in the assembly language of a new pipelined 16-bit microprocessor developed at the University of Florida, the Turbo9. TurbOS is derived from and incorporates the design benefits of an existing operating system called NitrOS-9, and reduces the code size from its progenitor by nearly 20%. Furthermore, it is over 80% smaller than the popular FreeRTOS operating system. TurbOS delivers a rich feature set for managing memory and process resources that are useful in SoC sub-block applications in an extremely small footprint of only 3 kilobytes.
Pitre et al. (Sat,) studied this question.