Wireless Networked Control Systems (WNCSs) require a special attention on communication protocols used to exchange time-constrained messages. The native IEEE 802.15.4 standard does not implement mechanisms capable to control the service offered by network. This paper proposes a solution enabling to prioritize the messages based on the blackburst mechanism. An analytic study on worst-case response time is presented to evaluate the performance of this new mechanism. Moreover, an online adaptation of the quality of control (QoC) is presented. These mechanisms are implemented and added to TrueTime and validated through simulations.