A multiprocessor system the kind in which two or more separate processor modules are interconnected for parallel processing includes two redundant interprocessor buses dedicated exclusively to interprocessor communication. Any processor module may send information to any other processor module by either bus. The multiprocessor system includes a memory system in which the memory of each processor module is divided into four logical address areas--user data, system data, user code and system code. The memory system includes a map which translates logical addresses to physical addresses and which coacts with the multiprocessor system to bring pages from secondary memory into primary main memory as required to implement a virtual memory system. The map also provides a protection function. It provides inherent protection among users in a multiprogramming environment, isolates programs from data and protects system programs from the actions of user programs. The map also provides a reference history information for each logical page as an aid to efficient memory management by the operating system.
This application is a division of parent application Ser. No. 721,043 filed Sept. 7, 1976 and entitled "Multiprocessor System" and claims the benefit of the filing date of the parent application now U.S. Pat. No. 4,228,496 issued on Oct. 14, 1980.
This circuit provides a minimally sized data transfer buffer interface between two central processing units for transferring data blocks of variable size. The circuit provides an indication to one CPU that the other CPU has received all the data words transmitted.
Embodiments of the present invention provide a memory arbiter for directing chipset and graphics traffic to system memory. Page consistency and priorities are used to optimize memory bandwidth utilization and guarantee latency to isochronous display requests. The arbiter also contains a mechanism to prevent CPU requests from starving lower priority requests. The memory arbiter thus provides a simple, easy to validate architecture that prevents the CPU from unfairly starving low priority agent and takes advantage of grace periods and memory page detection to optimize arbitration switches, thus increasing memory bandwidth utilization.
Apparatus for sharing data between processors having certain incompatible data formats is provided. A configurable data path unit and an address mapping unit allow a peripheral processor to access addressable storage locations within a host processor's main memory and store data types in a format so that the both processors can correctly access and interpret the data.
A memory management unit of use in a memory management system. The memory management unit selectively maps a logical address to a respective physical address in accordance with a selected one of a plurality of segment descriptors, each of which defines a logical-to-physical address mapping and a range of address spaces for which such mapping is valid. The mapping is achieved using an improved associative memory circuit. Means are provided to detect mapping conflicts between new segment descriptors and segment descriptors already stored, and to prevent the storage of such conflicting segment descriptors. A method and circuit are provided to coordinate the parallel operation of a plurality of the memory management units or the like.
A serial data mode circuit, which provides valid data on a falling edge of a data valid signal, uses time between falling edges to prepare for the next falling edge in order to reduce the time between when a falling edge of the data valid signal occurs and when data actually becomes valid. A plurality of interconnected flip-flops selectively enable data latches containing data in response to a rising edge of the data valid signal. The data is then provided to a tri-state driver prior to the falling edge of the data valid signal. The tri-state driver is then enabled in response to the falling edge of the data valid signal.
