Abstract: A computer system and method allow memory locations in both system memory and expansion memory devices coupled to an input/output (I/O) bus to be cacheable in a central processing unit (CPU) cache. The computer system contains an I/O bus connected to I/O devices and an expansion bus connected to expansion memory devices, a system memory not accessible via the I/O bus or expansion bus, and the system bus used for conducting data transfers between the I/O bus and both the CPU cache and system memory. The I/O bus supports data transfers between pairs of I/O devices, and I/O devices and expansion memory devices on the expansion bus, as well as data transfers between individual I/O devices and the system, which presents a problem of maintaining coherency in the CPU cache when data is written by one I/O device or expansion memory device to a cacheable memory location in another I/O device or expansion memory device.

Abstract: A computer system is provided, comprising system memory and a memory controller which resides on a system bus for controlling access to the system memory, a bus interface unit and a direct memory access controller also residing on the system bus, and a central processing unit electrically connected with the memory controller which is able to read and write data to the system memory via the memory controller. The memory controller and the bus interface unit each operate, when either is in control of the system bus, at a clock frequency which is a multiple of the clock frequency at which the direct memory access controller operates on the system bus. The memory controller and the bus interface unit each operate, when the direct memory access controller is in control of the system bus, at the same clock frequency as that of the direct memory access controller. The clock frequencies of the memory controller, the bus interface unit and the direct memory access controller are each synchronized in time.

Abstract: In a computer system that contains an input output (I/O) bus connecting to I/O devices, a central processing unit (CPU), a CPU cache memory, a system memory not directly accessible via the I/O bus, and a system bus used for conducting data transfers between the I/O bus and both the CPU cache and system memory, a method and apparatus are provided to allow addressable memory locations in both the system memory and I/O devices coupled to the I/O bus to be cacheable in the CPU cache. The I/O bus supports data transfers between pairs of I/O devices, as well as data transfers between individual I/O devices and the system which presents a problem of maintaining coherency in the CPU cache when data is written by one I/O device to a cacheable memory location in another I/O device.

Abstract: A bus interface unit for passing data between an I/O bus and a system bus in a dual bus computer system is provided. The bus interface unit has incorporated therein an address listing and compare function to determine whether a requesting device on the I/O bus is to read data from or write data to an address on the system bus. If so, the bus interface unit allows passing of the data therethrough. If not, the system bus is relinquished and the requesting device writes to the address on the I/O bus. Also, compare logic is incorporated in the bus interface unit which decodes system bus addresses originated from a system bus controller such as the DMA, to determine whether the destination of the transfer is to system memory or the I/O bus.

Abstract: A method and system are provided for controlling data transfer between a system memory connected to a system bus and at least one input/output (I/O) device connected to an I/O bus in a computer system. The system bus is coupled to the I/O bus by a bus interface unit comprising a first pair of buffers connected in series between the I/O bus and the system bus, and a second pair of buffers connected in series between the I/O bus and the system bus and in parallel with the first pair of buffers. Each of the buffers in each of the pairs is used for bidirectional data transfer between the system bus and the I/O bus.