  Energy consumption is a critical design issue in real-time systems,
especially in battery- operated systems. Maintaining high performance, while
extending the battery life between charges is an interesting challenge for
system designers. Dynamic Voltage Scaling (DVS) allows a processor to
dynamically change speed and voltage at run time, thereby saving energy by
spreading run cycles into idle time. Knowing when to use full power and when
not, requires the cooperation of the operating system scheduler. Usually,
higher processor voltage and frequency leads to higher system throughput while
energy reduction can be obtained using lower voltage and frequency. Instead of
lowering processor voltage and frequency as much as possible, energy efficient
real-time scheduling adjusts voltage and frequency according to some
optimization criteria, such as low energy consumption or high throughput, while
it meets the timing constraints of the real-time tasks. As the quantity and
functional complexity of battery powered portable devices continues to raise,
energy efficient design of such devices has become increasingly important. Many
real-time scheduling algorithms have been developed recently to reduce energy
consumption in the portable devices that use DVS capable processors. Three
algorithms namely Red Tasks Only (RTO), Blue When Possible (BWP) and Red as
Late as Possible (RLP) are proposed in the literature to schedule the real-time
tasks in Weakly-hard real-time systems. This paper proposes optimal slack
management algorithms to make the above existing weakly hard real-time
scheduling algorithms energy efficient using DVS and DPD techniques.
