Compiling for fine-grain concurrency: planning and performing software thread integration

Abstract

Embedded systems require control of many concurrent real-time activities, leading to system designs which feature multiple hardware peripherals with each providing a specific, dedicated service. These peripherals increase system size, cost, weight, power and design time. Software thread integration (STI) provides low-cost thread concurrency on general-purpose processors by automatically interleaving multiple (potentially real-time) threads of control into one. This simplifies hardware to software migration (which eliminates dedicated hardware) and can help embedded system designers meet design constraints such as size, weight, power and cost. The paper introduces automated methods for planning and performing the code transformations needed for integration of functions with more sophisticated control flows than in previous work. We demonstrate the methods by using Thrint, our post pass thread-integrating compiler, to automatically integrate multiple threads for a sample real-time embedded system with fine-grain concurrency. Previous work in thread integration required users to manually integrate loops; this is now performed automatically. The sample application generates an NTSC monochrome video signal (sending out a stream of pixels to a video DAC) with STI to replace a video refresh controller IC. Using Thrint reduces integration time from days to minutes and reclaims up to 99% of the system's fine grain idle time.