Semiconductor device with a hardware mechanism for proper clock control

1. A semiconductor device, comprising:

a clock generation unit which generates a clock signal;

a first module which asserts a clock-control request signal;

one or a plurality of second modules, each of which receives the clock signal and the clock-control request signal, and asserts a clock-control acknowledge signal after stopping an operation thereof, upon completion of a currently performed operation, in response to the assertion of the clock-control request signal;

an on-chip bus;

a plurality of modules connected to said on-chip bus; and

a bus arbiter which arbitrates a bus right between bus masters that are some of said plurality of modules, wherein said bus arbiter is one of said one or said plurality of second modules, and asserts the clock-control acknowledge signal as a response to the assertion of the clock-control request signal from said first module after refusing to grant the bus right to any one of the bus masters upon completion of a currently performed transfer operation on said on-chip bus,

wherein said clock generation unit selectively changes the clock signal supplied to said one or said plurality of second modules in response to assertion of all the clock-control acknowledge signals output from said one or said plurality of second modules including said bus arbiter.

2. The semiconductor device as claimed in claim 1 , wherein said clock generation unit selectively changes the clock signal by changing a frequency of the clock signal or stopping supply of the clock signal supplied to said one or plurality of second modules.

3. The semiconductor device as claimed in claim 1 , wherein said first module is a CPU core circuit.

4. The semiconductor device as claimed in claim 1 , wherein said first module asserts a clock-control enable signal to said clock generation unit in response to the assertion of all the clock-control acknowledge signals output from said one or plurality of second modules, and said clock generation unit selectively changes the clock signal in response to the assertion of the clock-control enable signal.

5. The semiconductor device as claimed in claim 1 , wherein said one or plurality of second modules consists of said bus arbiter.

6. The semiconductor device as claimed in claim 1 , further comprising:

an internal peripheral bus; and

a bus bridge which connects between said internal peripheral bus and said on-chip bus, wherein said bus bridge is one of said one or plurality of second modules, and asserts the clock-control acknowledge signal after refraining from performing a data transfer operation upon completion of a currently performed data transfer operation on said internal peripheral bus in response to the assertion of the clock-control request signal.

7. The semiconductor device as claimed in claim 6 , wherein said one or plurality of second modules consists of said bus arbiter and said bus bridge.

8. A method of clock control for a semiconductor device, comprising:

generating a clock signal;

asserting a clock-control request signal to one or a plurality of modules, each of which receives said clock signal and said clock-control request signal and asserts a clock-control acknowledge signal after stopping operation upon completion of a currently performed operation;

arbitrating a bus right between bus masters that are some of a plurality of modules connectable to an on-chip bus, on which a transfer operation is performable;

asserting said clock-control acknowledge signal as a response to the assertion of the clock-control request signal after refusing to grant the bus right to any one of the bus masters upon completion of a currently performable transfer operation; and

selectively changing the clock signal supplied to said one or said plurality of modules in response to the assertion of all said clock-control acknowledge signals output from said one or said plurality of modules.

9. An apparatus comprising:

means for generating a clock signal;

means for asserting a clock-control request signal to one or a plurality of modules, each of which receives said clock signal and said clock-control request signal and asserts a clock-control acknowledge signal after stopping operation upon completion of a currently performed operation;

means for arbitrating a bus right between bus masters that are some of a plurality of modules connectable to an on-chip bus, on which a transfer operation is performable;

means for asserting said clock-control acknowledge signal as a response to the assertion of the clock-control request signal after refusing to grant the bus right to any one of the bus masters upon completion of a currently performable transfer operation; and

means for selectively changing the clock signal supplied to said one or said plurality of modules in response to the assertion of all said clock-control acknowledge signals output from said one or said plurality of modules including said means for arbitrating a bus right.