Run-Time Slack Distribution for Real-Time Data-Flow Applications on Embedded MPSoC

Low energy consumption is crucial for embedded systems, including the ones that employ tiled Multiprocessor Systems-on-Chip(MPSoC). Such systems often execute real-time applications consisting of several tasks synchronized in a data-flow manner and mapped over different MPSoC tiles. Energy can be saved by lowering the processor voltage and frequency, hence extending the application execution over periods of time otherwise left idle, i.e., exploiting slack. In this paper we propose a framework to distribute slack information at run-time, intra-and inter-tile, to enable accurate and conservative slack calculation within each tile. The slack is transferred along with the existing inter-task synchronization and as a result it is distributed across the MPSoC with low overhead. In each tile, we add a hardware block that calculates the slack received during inter-tile communication and a software library to program this hardware. We integrate this framework into an existing MPSoC platform and we prototype an entire system with two tiles on an Xilinx ML605 FPGA board. We demonstrate the effectiveness of our proposal with a simple, conservative, DVFS management policy applied to an H.264 decoder application. The experimental results suggest that our framework reduces %the average processors frequency with 56% and the energy consumption with 53%, the total energy consumption of tiles with 27%, when compared to a state-of-the-art intra-tile approach that uses a similar management policy. Our proposal introduces only a minor software overhead of up to 4% over the application execution time and negligible additional FPGA chip utilization of 0.002%.