Full system emulation of approximate memory platforms with AppropinQuo

In this work we present an emulation framework for hardware platforms provided with approximate memory units, called AppropinQuo. The specific characteristic of AppropinQuo is to reveal the effects, on the hardware platform and on software, of errors introduced by approximate memory circuits and architectures. The emulator allows to execute software code without any modification with respect to the target physical board, since it includes the CPU, the memory hierarchy and the peripherals, capturing as well software-hardware interactions and faults due to approximate memory units. The final scope is reproducing the effects of errors generated by approximate memory circuits, allowing to evaluate the impact (quality degradation) on the output produced by the software. In fact, output quality is related to error rate, but their relationship strongly depends on the application, the implementation and its data representation on physical memory. The idea behind approximate memory circuits and approximate computing in general is to trade off energy consumption at the expense of computational accuracy and degradation of output quality. Memory is accounted for a large part of total power consumption in advanced architectures and it is supposed to increase as new memory hungry applications migrate toward the implementation on embedded systems (embedded machine learning, high definition video codecs, etc.). By relaxing design constraints regarding error probability on bit cells, researchers have proposed techniques that significantly reduce memory energy consumption. These techniques, which can be accounted in the general topic of approximate memory design, are implemented at circuit or architecture level, and are specific to the memory technology (i.e., SRAM or DRAM memories). However, the level of acceptable output degradation is the final metric that must be used to assess if, and to what extent, an approximate memory technique can be introduced. Our emulator allows to run actual applications as on the physical platform, to expose the effects of specific approximate memory circuits and architectures on output quality and to vary their parameters (e.g., error rate, number of affected bits, etc.). By exploring the approximate memory design space and its effects on the output of a software application, it is possible to characterize the application behavior, as a step toward the determination of the trade-off between saved energy and output quality (energy-quality tradeoff).