In a multi-many/core system, the Network-on-Chip (NoC) based communication backbone is responsible for a relevant fraction of the overall energy budget. Reducing the voltage swing for signaling in crossbars and links results in significant energy saving. Unfortunately, as voltage swing reduces, the bit-error-rate increases, that in turn compromises the communication reliability. Starting from the assumption that not all the communications need same level of reliability, in this paper we propose techniques and architectures for run-time tuning of the voltage swing of the crossbars and inter-router links. The proposed technique, is compared with the state of the art in link energy reduction through data encoding under both synthetic and real traffic scenarios. We found that the proposed techniques allow to significantly reduce the energy consumption of the NoC fabric without degrading the performance metrics. Energy savings ranging from 20% to 43% have been observed without any relevant impact on the performance metrics.