A system LSI dynamically and speedily controls clocks of various frequencies
as
used in a wide range of operation modes from high-speed to low-speed operation
modes, enabling user selection of a system of power consumption type most suitable.
The system LSI includes a ROM that stores a clock control library for carrying
out clock state transitions between ordinary operation modes; and a system control
circuit having a register for carrying out clock state transitions between ordinary
operation modes and special modes responsive to changes in value of the register,
and also carrying out clock state transitions among ordinary operation modes responsive
to the clock control library. Calling of the clock control library and changing
of the register value are controlled by an application program. The main library
of the clock control library is described and called using C language.
