Supply voltages within a data processing system may be controlled by a
voltage control module which can provide digital signals to a power
management unit to cause changes in supply voltages without software
intervention. For example, in one embodiment, a voltage control signal
and a standby signal may be provided to control the supply voltages
output by a voltage regulator within the power management unit. In one
embodiment having multiple processors, a voltage control signal and a
standby signal corresponding to each processor may be provided to the
power management unit which has a voltage regulator supplying an
independently controlled supply voltage to each processor. Alternatively,
a voltage regulator, a voltage control signal, and a standby signal may
be shared by multiple processors, where the voltage control module may
ensure that the supply voltage is changed only when the change is
appropriate for all processors sharing the same voltage regulator.