Abstract: A multiprocessor system includes a number of subsystems all coupled in common to an asynchronous system bus. Apparatus is included in the system bus interface logic of each processing subsystem to receive commands from the system bus and compare the interrupt priority level of the new command with the current command being executed. If the new command has a lower interrupt priority than the current command, then the subsystem sending the command will receive a not acknowledge response from the processing system. The apparatus is responsive to certain control signals from the new command to bypass the interrupt priority comparison logic and initiate an immediate interrupt regardless of the interrupt priority level of the current command being executed by the processing subsystem. The processing subsystem may also generate a command to itself via the system bus which requires the high speed interrupt.

Abstract: A cache memory subsystem has multilevel directory memory and buffer memory pipeline stages shared by at least a pair of independently operated central processing units and a first in first out (FIFO) device which connects to a system bus of a tightly coupled data processing system. The cache subsystem includes a number of programmable control circuits which are connected to receive signals representative of the type of operations performable by the cache subsystem. These signals are logically combined for generating an output signal indicating whether or not the contents of the directiory memory should be flushed when any one of a number of types of address or system faults has been detected in order to maintain cache coherency.

Abstract: An apparatus is included within the bus interface circuits of each processing unit of a multiprocessing system which connect in common with the other units of the system to an asynchronous system bus. The apparatus and interrupt signal couple to the processing unit's level register and interrupt circuits. In response to a command specifying a level change, the apparatus conditions these circuits to store level and interrupt signals applied to the system bus as part of such CPU command during a bus cycle of operation granted to the processing unit on a priority basis. This ensures the reliable switching between interrupt levels and the notification of such level changes to the other units of the system without interference from other processing units.

Abstract: An address path which transfers addresses from a number of sources includes an incrementing circuit. The address includes a plurality of address bits and integrity bits. The address bits are applied to the incrementing circuit while the integrity bits are applied in parallel to a programmable logic device (PLD). While the address is being transferred or incremented as required, the PLD independently generates a number of transform bits defining a characteristic of the number of address bits predicted to change state. Thereafter, the transform bits are used to transform the address integrity bits for transfer with the incremented address. The incremented address, transform bits and integrity bits are logically combined for verifying that the address was transferred and/or incremented without error.

Abstract: A cache memory subsystem couples to main memory through interface circuits via a system bus in common with a plurality of central processing subsystems which have similar interface circuits. The cache memory subsystem includes multilevel directory memory and buffer memory pipeline stages shareable by at least a pair of processing units. A read in process (RIP) memory associated with the buffer memory stage is set to a predetermined state in response to each read request which produces a miss condition to identify the buffer memory location of a specific level in the buffer memory which has been preallocated. The contents of the buffer memory stage are maintained coherent with main memory by updating its contents in response to write requests applied to the system bus by other subsystems. Upon detecting the receipt of data prior to the receipt of the requested data which would make the buffer memory contents incoherent, the cache switches the state of control means associated with the RIP memory.

Abstract: A data processing system includes a plurality of units which are coupled to transfer requests including data, command and integrity signals between units over a system bus during allocated bus transfer cycles. Each unit includes response apparatus for acknowledging requests received from other units. Each of a number of units further includes retry apparatus and like checking apparatus for verifying that the different parts of a request received from such unit over the bus are valid based upon the states of accompanying function identification signals. When less than all of the parts of the request defined as requiring verification are detected as valid, the receiving unit does not accept the request and inhibits its response apparatus from generating a response. This prevents damage to system integrity and permits each unit with retry apparatus to retry the request during a subsequent bus transfer cycle.

Abstract: A data processing system includes a plurality of units which are coupled to transfer requests including data, command and integrity signals between units over a system bus during allocated bus transfer cycles. Each unit includes response apparatus for acknowledging requests received from other units. Each of a number of units further includes retry apparatus and checking apparatus for verifying that all of the parts of a request received from such unit over the bus are valid. When less than all of the parts of the request are detected as valid, the receiving unit does not accept the request and inhibits its response apparatus from generating a response. This prevents damage to system integrity and permits each unit with retry apparatus to retry the request during a subsequent bus transfer cycle.

Abstract: A data processing system has a system bus network which includes a distributed priority network for transferring data asynchronously between a number of subsystems which couple to the bus. Each subsystem includes priority logic circuits coupled to receive a group of priority signals from the priority network which establish when the subsystem has the highest priority of the requesting subsystems to access the bus. The number of subsystems include a plurality of identical subsystems, each of which has a channel number assignment apparatus. The apparatus of each identical subsystem is connected to receive the same of at least one of the group of priority signals. During the idle state of the system bus, the apparatus of each identical subsystem operates to store a unique state of the priority signal which is defined as a function of the subsystem's position on the bus thereby automatically establishing a unique channel number value for each identical subsystem.

Abstract: A data processing system includes a plurality of memory command generating units which connect to a common bus network with a number of memory subsystems. Each subsystem includes a controller which controls the operation of a number of memory module units and includes a number of queue circuits for storing memory requests to be processed. The memory controller further includes control apparatus connected to monitor bus activity. In response to certain bus activity conditions occurring during multiword transfer operations, the control apparatus operates to lengthen the time between successive multiword transfers of data to the bus so as to ensure that new requestors having lower priorities than a memory controller gain access to an available queue notwithstanding the amount of bus delay incurred in transmitting their memory requests.

Abstract: A memory controller couples to a bus and controls a number of memory module units or memory modules. The controller includes a number of queue circuits for processing a variety of different types of memory requests received from a number of command generating units coupled to the bus requiring the controller to operate in a corresponding number of different modes. The controller includes queue start timing control apparatus which couples to the modules and to the queue circuits for resolving conflicts between the types of requests and the internal operations required to be performed by the controller within a minimum of time.

Abstract: A cache memory wherein data words identified by odd address numbers are stored separately from data words identified by even address numbers. A group of diagnostic control registers supply signals for controlling the testing of the cache within the cache memory to determine the operability of the individual elements included in the cache memory.

Abstract: In a data processing system, a system memory includes first memory modules having a data path of a first bit width and second memory modules having a data path of a second bit width with the first bit width being less than the second bit width. A central subsystem includes a cache memory unit and processing units for initiating requests for data transfers of the second bit width between the system memory and the subsystem processing units. An interface coupling the system memory and the central subsystem for bidirectional data transfers generates, in response to a memory request of a second bit width wherein the requested data is stored in a first memory module, additional memory requests until sufficient data has been retrieved from the system memory to satisfy the central subsystem request.

Abstract: A logic system in an intersystem link (ISL) unit accommodating the transfer of binary coded information between communication busses in a data processing system is disclosed, wherein dedicated locations in a file register are selected at the bus rate in response to binary coded information received from a local communication bus. ISL transactions to be initiated in response to bus cycle requests thereby are identified. ISL transactions are handled in parallel, and memory transfers are segregated from non-memory transfers to avoid unnecessary delays in memory transfers.

Abstract: A logic system referred to as an intersystem link unit (ISL) is provided for accommodating the transfer of binary coded information between two or more communication busses in a data processing system, wherein information including memory and non-memory read and write requests, CPU to CPU interrupts, peripheral control units to CPU interrupts may be transferred between plural communication busses each supporting plural data processing units including plural CPUs without substantially affecting the bus rate of the individual communication busses. Binary coded information from a communication bus is acquired asynchronously, and plural bus communications of different types are accommodated in parallel. The ISL units further may be dynamically reconfigured to provide for a reallocation of communication bus resources between communication busses.

Abstract: A common electrical bus for coupling a plurality of units in a data processing system for the transfer of information therebetween. The units are coupled in a priority arrangement which is distributed thereby providing priority logic in each of the units and allowing bus transfer cycles to be generated in an asynchronous manner. Each of the units includes priority logic which includes logic elements for requesting a bus cycle, such request being granted if no other higher priority unit has also requested a bus cycle. The request for and an indication of the grant of the bus cycle are stored in each unit so requesting and being granted the bus cycle respectively, only one such unit being capable of having the grant of a bus cycle at any given time, whereas any number of such units may have its request pending at any particular time.

Abstract: A main memory system includes encoder and decoder circuits. The encoder circuits are connected to receive data bits and parity bits and from them generate check code bits which are stored with the data bits during a write cycle of operation. The decoder circuits are connected to receive data and check bits read out from memory during a read cycle of operation. The decoder circuits include a plurality of decoder circuits and error locator circuits. Circuits via exclusive OR circuits generate a number of syndrome bit signals. These signals are divided into first and second groups. The first group is coded to specify which one of a number of decoder circuits comprising the error locator circuits is to be enabled in the case of an error condition. The second group of signals is coded to designate the particular data bit to be corrected by the decoder circuits.

Abstract: Apparatus and method are included in the main memory of the data processing system which receives data from a plurality of input/output devices connected to a common bus. During a write cycle of operation, a device applies a plurality of data byte signals together with associated parity bits for writing into an addressed storage location of memory. Error detection and correction encoder circuits are connected to receive the data bits and parity bits and from them generate check code bits which are coded to signal selectively the presence of an uncorrectable error condition in accordance with the parity bits from a given source.

Abstract: A microprogrammable peripheral controller in addition to being operative to controlling plurality of input/output devices in response to commands for processing information signals from a magnetic medium also includes apparatus for independently establishing a minimum operating capability within the controller. The apparatus includes a read-only control store arranged to store microinstructions and a limited number of basic bit patterns. The apparatus in response to an external control signal is operative to condition the data recovery apparatus included in the controller to receive the blocks of synchronization and data patterns arranged in a predetermined format and generated from basic bit patterns obtained from the control store. Simultaneously therewith, the apparatus inhibits normal transfer of information from the magnetic medium.

Abstract: A plurality of logic boards coupled together over a common electrical bus by use of a plurality of connectors, at least one per board, which includes at least one pair of terminals for coupling an interlock signal wire which is daisy chained through each of such boards and connectors. By providing a known signal state on the interlock signal wire at one end of the bus, an improper connection or an error condition in one of the logic boards will be indicated by a sensor, which may be included at the last logic board, if the known signal state is not received at the sensor.

Abstract: A common electrical bus is provided for coupling a plurality of units in a data processing system for transfer of information therebetween. The units are coupled in a priority arrangement which is distributed in each of the units thereby making a bus monitor unnecessary. The bus transfer cycles are generated in an asynchronous manner.