Computer system using stop clock function of CPU to enter low power state

• US 6,317,841 B1
• Filed: 05/08/1998
• Issued: 11/13/2001
• Est. Priority Date: 05/30/1995
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Senuma, Koichi, Nagae, Akihito, Iguchi, Takeyuki
• Primary Examiner(s): Sheikh, Ayaz
• Assistant Examiner(s): Jean, Frantz B.
• Application Number:
  US09/074,514
• Time in Patent Office: 1,285 Days
• Field of Search: 713/322, 713/320, 713/324, 713/501, 713/502, 713/600, 713/300
• US Class Current: 713/322
• CPC Class Codes: G06F 1/3228 Monitoring task completion, e.g. by use of idle timers, stop commands or wait commands
• CPC Class Codes: G06F 1/3237 by disabling clock generation or distribution
• CPC Class Codes: G06F 1/324 by lowering clock frequency
• CPC Class Codes: Y02D 10/00 Energy efficient computing, e.g. low power processors, power management or thermal management

Abstract

The CPU speed is apparently decreased, and current consumption is reduced by asserting a stop clock (STPCLK#) signal at a predetermined interval. When a system event (INTR, NMI, SMI, SRESET, and INIT) occurs, assertion of the STPCLK# signal is inhibited for a predetermined time to allow a high-speed operation. In an ISA refresh cycle, by asserting the STPCLK# signal instead of a conventional HOLD/HLDA cycle, the refresh cycle is executed in a stop grant state.

Claims

1. A computer system comprising:

a central processing unit (CPU) coupled to receive a signal which stops an internal clock of the CPU;

means for periodically asserting the signal to set the CPU in a low power state; and

a circuit, coupled to the CPU, for blocking the assertion of a system event request with respect to the CPU while the signal is asserted, wherein the circuit holds the system event request, breaks the assertion of the signal in response to the held system event request, and then outputs the held system event request to the CPU after the assertion of the signal is broken.

2. The system according to claim 1, wherein the signal is a stop clock signal (STPCLK).

3. The system according to claim 2, further comprising a timer for counting, in response to the break of the STPCLK signal, a predetermined period of time during which the assertion of the STPCLK is blocked.

4. A computer system comprising:

a central processing unit (CPU) coupled to receive a signal which stops an internal clock of the CPU;

means for periodically asserting the signal to set the CPU in a lower power state; and

a circuit, coupled to the CPU, for blocking the assertion of and holding a system event request with respect to the CPU while the CPU is in a stop grant state, and releasing the system event request with respect to the CPU after the stop grant state is broken.

5. The system according to claim 4, wherein the signal is a stop clock (STPCLK).

6. The system according to claim 4, wherein the system event request includes at least one of a system management interrupt (SMI) request, a non-maskable interrupt (NMI) request, an Interrupt Request (INTR), and a hold request.

7. A circuit comprising:

a first circuit for outputting a signal which periodically stops an internal clock of a central processing unit (CPU) to the CPU, the signal being periodically asserted; and

a second circuit for receiving a system event request with respect to the CPU,

wherein the first and second circuit hold the system event request, break the assertion of the signal in response to the held system event request, and then output the held system event request to the CPU after the assertion of the signal is broken.

8. The circuit according to claim 7, wherein the signal is a stop clock signal (STPCLK).

9. The circuit according to claim 7, wherein said first and second circuit are arranged in a gate array.

10. The circuit according to claim 7, wherein the system event request includes at least one of a system management interrupt (SMI) request, a non-maskable interrupt (NMI) request, an Interrupt Request (INTR), and a hold request.