Semiconductor device

• US 5,987,616 A
• Filed: 09/24/1997
• Issued: 11/16/1999
• Est. Priority Date: 05/23/1997
• Status: Expired due to Term

• Current Assignee: Renesas Electronics Corporation
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Suzuki, Hiroaki
• Primary Examiner(s): Pan, Daniel H.
• Application Number:
  US08/936,627
• Time in Patent Office: 783 Days
• Field of Search: 395/800.17, 395/800.35, 395/800.01, 395/381, 395/561, 395/800.36, 395/384, 395/750.06, 395/750.3, 395/842, 381/312, 702/65, 708/523, 708/620, 712/43, 712/208, 710/14, 710/74, 713/320, 713/300, 713/321, 713/324, 713/322
• US Class Current: 713/320
• CPC Class Codes: G06F 1/32 Means for saving power

Abstract

In order to reduce a leak current, a processor core unit decodes an instruction fetched by an instruction fetch portion and turns off a leak cut switch for an unused function block of function blocks according to the result of decoding, whereby the supply of power to the corresponding function block is cut off.

Claims

1. A semiconductor device comprising:

a processor core unit, said processor core unit including,

an instruction fetch portion for fetching both or one of an instruction and data;

a decoder for decoding an instruction fetched by said instruction fetch portion;

a plurality of function blocks divided by processing functions;

leak cut switches for respectively cutting off the supply of power to said function blocks, which are provided for each function block; and

a power management unit for analyzing both or one of the instruction and the data and generating a control signal for turning off a respective leak cut switch of said leak switches for a non-used function block of said plurality of function blocks.

2. A semiconductor device according to claim 1, wherein said decoder is divided into at least a predecoder for classifying instructions and allocating function blocks for processing the instructions and local decoders for respectively decoding the instructions allocated to the individual function blocks, leak cut switches for cutting off the supply of power to the local decoders are provided every local decoders, and said power management unit generates a control signal for turning off the leak cut switch for a non-used local decoder of said local decoders.

3. A semiconductor device according to claim 1, wherein said processor core unit includes an instruction queue unit for temporarily retaining each of instructions and wherein said power management unit analyzes the instruction prior to the execution of the instruction and previously generates a control for turning off the leak cut switch for the non-used function block of said plurality of function blocks.

4. A semiconductor device according to claim 1, wherein said power management unit generates control signals for turning off the leak cut switches for all the circuit units other than said instruction fetch portion of said processor core unit when the instruction is defetched by said instruction fetch portion.

5. A semiconductor device according to claim 1, wherein input/output devices of said processor core unit are divided into at least two blocks for upper-order and lower-order bits, leak cut switches are provided for the divided input/output devices for the upper-order and lower-order bits respectively, and said power management unit generates control signals for turning off the leak cut switches used for said input/output devices when said input/output devices are not in use.

6. A semiconductor device according to claim 1, wherein bus driver circuits of said processor core unit are divided into at least a bus driver circuit for an upper-order bit bus and a bus driver circuit for a lower-order bit bus, leak cut switches are provided for the divided bus driver circuits for the upper-order and lower-order bit buses respectively, and said power management unit generates control signals for turning off the leak cut switches used for said bus driver circuits when said upper-order and lower-order bit buses are not in use.