Abstract: An I/O subsystem having a processor, a bridge unit, and an I/O messaging unit that couple a primary, secondary and tertiary bus in a computer system. The bridge unit is configurable to claim requests that access a messaging unit (MU) address range from the secondary bus, the MU itself being coupled to the primary bus. The MU interrupts the processor when an I/O request is posted, in response to which the processor reads from the MU pointers to an I/O messages and may then execute the I/O message. To promote the portability of software written for agents on either the primary or the secondary bus that wish to access the MU, the primary and secondary address translation units of the I/O subsystem are programmed to claim the same address translation window, where the MU address range is a portion of the primary ATU address translation window, and the secondary ATU is configured to not claim requests within the MU address range.

Abstract: An I/O subsystem having a processor, a bridge unit, and an I/O messaging unit that couple a primary, secondary and tertiary bus in a computer system. The bridge unit is configurable to claim requests that access a messaging unit (MU) address range from the secondary bus, the MU itself being coupled to the primary bus. The MU interrupts the processor when an I/O request is posted, in response to which the processor reads from the MU pointers to an I/O messages and may then execute the I/O message. To promote the portability of software written for agents on either the primary or the secondary bus that wish to access the MU, the primary and secondary address translation units of the I/O subsystem are programmed to claim the same address translation window, where the MU address range is a portion of the primary ATU address translation window, and the secondary ATU is configured to not claim requests within the MU address range.

Abstract: A method and apparatus for providing an efficient, low cost data streaming mechanism from a first bus architecture to a second bus architecture across a bus bridge. Separate read and write data queues are provided in the bus bridge for transfer of data in both directions, and the speed of one of the buses is increased over the speed of the other one of the buses. In one embodiment, the first bus is a PCI bus and the second bus is an internal CPU bus.

Abstract: A PCI-to-PCI bridge having a processor configured for performing various routing mode operations based upon the addresses of transactions carried on interconnected PCI buses. The various routing modes operate on decoded PCI addresses and are known as “programmable decode modes.” In one programmable decode mode, private address spaces are defined for allowing two or more devices interconnected to a secondary PCI bus to communicate directly using private transactions. In another programmable decode mode, subtractive routing operations are provided wherein a secondary PCI interface captures any transactions not claimed on the secondary PCI bus after a predetermined number of clock cycles. Another programmable decode mode is “intelligent” bridging wherein conventional inverse positive decode operations are disabled for the entire primary address space of the secondary PCI bus.

Abstract: Method and apparatus for tuning the performance of bridge devices, including PCI-to-PCI bridges as well as PCI local bus bridges (or host bridges). The embodiments of the invention permit a multiple-bus computer system to be tuned in view of the application and the bridge queue sizes. Such applications include those concerned with raw bandwidth (such as disk storage), and those that are sensitive to latency (such as networking and videoconferencing). The embodiments of the invention feature a control register that specifies storage conditions to be met by the read and write queues of the bridge. The programmed storage conditions are trigger points which cause the bridge to transfer data into or remove data from the queues during read and write transactions in order to promote the performance (throughput or latency) desired from the bridge.

Abstract: A PCI-to-PCI having programmable decode modes comprising at least one of a standard bridge data transfer transaction, an intelligent bridge data transfer transaction, and a private address space data transfer transaction, and wherein the transactions are configured to bypass a host bus.

Abstract: A computer system is described having one or more host processors, a host chipset and a input/output (I/O) subsystem. The host processors are connected to the host chipset by a host bus. The host chipset is connected to the input/output subsystem by a primary personal computer interface (PCI) bus. The I/O subsystem is connected to I/O devices by a secondary PCI bus. The I/O subsystem includes advanced programmable interrupt controller (APIC) functionality typically provided within an I/O APIC chip within a host chipset. The APIC functionality of the I/O subsystem is primarily implemented in software executing on a core processor of the I/O subsystem. The software creates and accesses various APIC registers and tables, such as a redirection table, within a memory of the I/O subsystem. A single 3-wire APIC bus interconnects the host processors with the I/O subsystem. With this arrangement, non-PCI interrupt lines from the I/O devices are connected only into the I/O subsystem, rather than into the host chipset.

Abstract: A PCI-to-PCI bridge is described having a processor configured for performing various routing operations based upon the addresses of transactions carried on interconnected PCI buses. The various routing modes operate on decoded PCI addresses and are described herein as "programmable decode modes." In one programmable decode mode, private address spaces facilitate communication between peer PCI devices without burdening the primary PCI bus or any upstream components such as a host-to-PCI bridge, a host bus and host microprocessors. In another programmable decode mode, subtractive routing operations are provided wherein a secondary PCI interface captures any transactions not claimed on the secondary PCI bus after a predetermined number of clock cycles. The transactions are routed to the primary PCI bus. Another programmable decode mode is "intelligent" bridging wherein conventional inverse positive decode operations are disabled for the entire primary address space of the secondary PCI bus.