A clock control hierarchy is provided that is comprised of synchronous and
asynchronous hold request signals that are used to start and stop
functional units of a chip. Pervasive logic is provided that uses a
synchronous "chip hold" signal and asynchronous latch/functional unit
hold signals to individually target functional units and latches that are
to remain in a held state once the "chip hold" state is released. With
the present invention, a chip hold request is first activated followed by
scannable latch and non-scannable latch hold requests being activated to
identify which latches will be clocked or not clocked when the chip hold
is released. Functional unit hold signals are activated to place certain
ones of the functional units of the chip in a hold state. The chip hold
request is deactivated and the chip operates with the selected functional
units and latches being maintained in a held state.