Video subsystem power management apparatus and method
First Claim
1. A method of reducing power consumption in a video subsystem of a computer, comprising the steps of:
- inactivating a pixel clock which drives a RAMDAC, thereby reducing power consumed by the RAMDAC; and
decreasing the frequency of a memory clock for driving a video controller by a predetermined factor, thereby reducing the power consumed by the video controller.
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Accused Products
Abstract
Power is conserved in a video subsystem by inactivating a pixel clock (PCLK) and reducing frequency of a memory clock (MCLK) responsive to an indication of user inactivity. The inactivation of PCLK reduces the power consumed in the RAMDAC, frame buffer, phase lock loop (PLL) clock circuit, and to a smaller extent, the video controller. Reducing the frequency of MCLK conserves power in the video controller and the PLL, In order to maintain the integrity of the data in the frame buffer, the refresh rate programmed by the video controller is increased to offset the reduction of the MCLK frequency. Significant power savings can be accomplished with minimal BIOS or video controller programming and minimal transfer of state information prior to power-down.
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Citations
21 Claims
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1. A method of reducing power consumption in a video subsystem of a computer, comprising the steps of:
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inactivating a pixel clock which drives a RAMDAC, thereby reducing power consumed by the RAMDAC; and decreasing the frequency of a memory clock for driving a video controller by a predetermined factor, thereby reducing the power consumed by the video controller. - View Dependent Claims (2, 3, 5, 6)
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4. The method of claim I wherein said step of decreasing the memory clock frequency comprises the step of programming a phase lock loop clock circuit to output a clock at a predetermined frequency responsive to a data word from the video controller.
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7. A method of reducing power consumption in a video subsystem of a computer, comprising the steps of:
- increasing the rate at which a video controller refreshes memory in a frame buffer by a predetermined factor; and
decreasing the frequency of a memory clock for driving the video controller by the predetermined factor, thereby reducing the power consumed by the video controller and reducing the frequency of memory cycles to a frame buffer, while maintaining a normal refresh rate. - View Dependent Claims (8, 9, 10, 11)
- increasing the rate at which a video controller refreshes memory in a frame buffer by a predetermined factor; and
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12. Circuitry for providing a video subsystem with power conservation capabilities, comprising:
- clock circuitry for programmably generating a first clock and a second clock, such that said first clock can be disabled responsive to a first control signal and said second clock can be reduced in frequency responsive to a second control signal;
a frame buffer memory;a RAMDAC driven by said first clock coupled to said frame buffer, the power consumed by said RAMDAC dependent upon the frequency of said first clock; a video controller driven by said second clock and coupled to said frame buffer, said video controller controlling memory cycles in said frame buffer responsive to said second clock; and circuitry for inactivating said first clock and reducing the frequency of said second clock responsive to an indication of inactivity to reduce power consumption in said clock circuitry, said frame buffer and said RAMDAC. - View Dependent Claims (13, 14, 15, 16, 17, 18)
- clock circuitry for programmably generating a first clock and a second clock, such that said first clock can be disabled responsive to a first control signal and said second clock can be reduced in frequency responsive to a second control signal;
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19. A computer system for minimizing power consumption in a video subsystem comprising:
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a CPU connected to a bus; a plurality of peripherals connected to said CPU by the bus; and a video subsystem connected to a video monitor and connected to said CPU by the bus, comprising; a frame buffer comprising dynamic memory; a clock circuit for generating a PCLK clock and a MCLK clock, and for disabling said PCLK clock and for decreasing a frequency of said MCLK clock in response to an inactivity signal; a RAMDAC, connected to said frame buffer and to said clock circuit, driven by said PCLK clock; and a video controller, driven by said MCLK clock, for programmably controlling a dynamic memory refresh rate of said frame buffer and for increasing the dynamic memory refresh rate to offset a decrease in the frequency of said MCLK clock in order to maintain the normal refresh rate of the dynamic memory. - View Dependent Claims (20, 21)
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Specification