摘要:
A power management circuit for managing low power modes in a computer system, which implements four power modes, from highest power consumption to lowest power consumption: RUN mode, SLEEP mode, IDLE mode, and STANDBY mode. The computer system includes a PCI bus and an ISA bus, with a CPU-PCI bridge to connect the host bus and the PCI bus and a PCI-ISA bridge to connect the PCI bus and the ISA bus. The power management circuit transitions from SLEEP mode to IDLE mode by first determining if the CPU-PCI bridge is parked on the PCI bus and if it is in SLEEP mode. The power management circuit then waits for one refresh period and for all internal queues to empty before checking again to determine if the CPU-PCI bridge is still parked on the PCI bus and if it is still in SLEEP mode. If true, the CPU-PCI bridge transitions to IDLE mode. The power management circuit also performs low power refresh cycles when it is in IDLE or STANDBY mode. In those modes, the memory controller in the CPU-PCI bridge is disabled to conserve power. The power management circuit performs the refresh cycles based off an external asynchronous clock. Further, the power management circuit drives certain PCI bus signals to a certain state to avoid leakage current due to the existence of a mixture of 3.3-volt and 5-volt components connected to the PCI bus.
摘要:
A power management circuit for managing low power modes in a computer system, which implements four power modes, from highest power consumption to lowest power consumption: RUN mode, SLEEP mode, IDLE mode, and STANDBY mode. The computer system includes a PCI bus and an ISA bus, with a CPU-PCI bridge to connect the host bus and the PCI bus and a PCI-ISA bridge to connect the PCI bus and the ISA bus. The power management circuit transitions from SLEEP mode to IDLE mode by first determining if the CPU-PCI bridge is parked on the PCI bus and if it is in SLEEP mode. The power management circuit then waits for one refresh period and for all internal queues to empty before checking again to determine if the CPU-PCI bridge is still parked on the PCI bus and if it is still in SLEEP mode. If true, the CPU-PCI bridge transitions to IDLE mode. The power management circuit also performs low power refresh cycles when it is in IDLE or STANDBY mode. In those modes, the memory controller in the CPU-PCI bridge is disabled to conserve power. The power management circuit performs the refresh cycles based off an external asynchronous clock. Further, the power management circuit drives certain PCI bus signals to a certain state to avoid leakage current due to the existence of a mixture of 3.3-volt and 5-volt components connected to the PCI bus.
摘要:
A power management circuit for managing low power modes in a computer system, which implements four power modes, from highest power consumption to lowest power consumption: RUN mode, SLEEP mode, IDLE mode, and STAND BY mode. The computer system includes a PCI bus and an ISA bus, with a CPU-PCI bridge to connect the host bus and the PCI bus and a PCI-ISA bridge to connect the PCI bus and the ISA bus. The power management circuit transitions from SLEEP mode to IDLE mode by first determining if the CPU-PCI bridge is parked on the PCI bus and if it is in SLEEP mode. The power management circuit then waits for one refresh period and for all internal queues to empty before checking again to determine if the CPU-PCI bridge is still parked on the PCI bus and if it is still in SLEEP mode. If true, the CPU-PCI bridge transitions to IDLE mode. The power management circuit also performs low power refresh cycles when it is in IDLE or STANDBY mode. In those modes, the memory controller in the CPU-PCI bridge is disabled to conserve power. The power management circuit performs the refresh cycles based off an external asynchronous clock. Further, the power management circuit drives certain PCI bus signals to a certain state to avoid leakage current due to the existence of a mixture of 3.3-bolt and 5-volt components connected to the PCI bus.
摘要:
A power management circuit for managing low power modes in a computer system, which implements four power modes, from highest power consumption to lowest power consumption: RUN mode, SLEEP mode, IDLE mode, and STANDBY mode. The computer system includes a PCI bus and an ISA bus, with a CPU-PCI bridge to connect the host bus and the PCI bus and a PCI-ISA bridge to connect the PCI bus and the ISA bus. The power management circuit transitions from SLEEP mode to IDLE mode by first determining if the CPU-PCI bridge is parked on the PCI bus and if it is in SLEEP mode. The power management circuit then waits for one refresh period and for all internal queues to empty before checking again to determine if the CPU-PCI bridge is still parked on the PCI bus and if it is still in SLEEP mode. If true, the CPU-PCI bridge transitions to IDLE mode. The power management circuit also performs low power refresh cycles when it is in IDLE or STANDBY mode. In those modes, the memory controller in the CPU-PCI bridge is disabled to conserve power. The power management circuit performs the refresh cycles based off an external asynchronous clock. Further, the power management circuit drives certain PCI bus signals to a certain state to avoid leakage current due to the existence of a mixture of 3.3-bolt and 5-volt components connected to the PCI bus.
摘要:
A computer system includes a bus bridge which provides an interface between a main memory and a peripheral bus such as a PCI bus. A peripheral bus interface unit is provided which supports delayed transactions. When a PCI bus master effectuates a read cycle to read data from main memory on the PCI bus, the peripheral bus interface detects the read cycle and terminates or retries the transaction on the PCI bus. The peripheral bus interface further requests the read data from main memory and places the read data in a buffer. When the PCI master device re-attempts the read transaction, the peripheral interface provides the read data directly from its delayed read buffer. When the peripheral bus interface retries the PCI master that establishes a delayed read operation, the peripheral bus interface asserts a control signal referred to the delayed cycle signal. A PCI arbiter which controls ownership of the PCI bus receives the delayed cycle signal and, in response to its assertion, lowers a level of arbitration priority provided to the PCI master establishing the delayed read. In one embodiment, the PCI arbiter inhibits ownership of the PCI bus by the master establishing the delayed read in response to assertion of the delayed cycle signal. When the peripheral bus interface receives the read data and is ready to deliver it to the PCI bus, the delayed cycle signal is deasserted (or strobed). The PCI bus arbiter detects this deassertion (or strobing) of the delayed cycle signal and responsively raises a level of arbitration priority to the PCI master establishing the delayed read. In one implementation, upon detecting the deassertion of the delayed cycle signal, the PCI bus arbiter provides a highest level of arbitration priority to the PCI master establishing the delayed read. The delayed read operation then completes when the PCI master re-initiates the read cycle. The optimized arbitration technique may similarly be employed during other delayed transactions, such as memory writes, I/O read or writes, and configuration reads or writes.
摘要:
A PCI bridge is configured to perform delayed read operations in response to a memory read initiated on the PCI bus. Normally, the PCI bridge is configured to discard delayed read data read from main memory following a predetermined discard count time after the PCI master establishing the delayed read operation is retried on the PCI bus. The computer system further includes a secondary bus bridge such as an ISA bridge for providing an interface between the PCI bus and an ISA bus. When an ISA device desires to read data from the main memory, the ISA bridge asserts a flush request signal. The PCI bridge responsively flushes any pending CPU to PCI transactions pending within the PCI bridge. When the flushing operation is complete, the PCI bridge asserts an acknowledge signal. A PCI arbiter for arbitrating ownership of the PCI bus may increase a level of arbitration priority provided to the ISA bridge in response to assertion of the acknowledge signal. The PCI bridge is advantageously configured to decrease the time associated with discarding of the delayed read data when the acknowledge signal is asserted.