  In distributed control systems where devices are connected through Wi-Fi,
direct access to low-level MAC operations may help applications to meet their
timing constraints. In particular, the ability to timely control single
transmission attempts on air, by means of software programs running at the user
space level, eases the implementation of mechanisms aimed at improving
communication timeliness and reliability. Relevant examples are deterministic
traffic scheduling, seamless channel redundancy, rate adaptation algorithms,
and so on. In this paper, a novel architecture is defined, we call SDMAC, which
in its current embodiment relies on conventional Linux PCs equipped with
commercial Wi-Fi adapters. Preliminary SDMAC implementation on a real testbed
and its experimental evaluation showed that integrating this paradigm in
existing protocol stacks constitutes a viable option, whose performance suits a
wide range of applications characterized by soft real-time requirements.
