Abstract: In a data processing system in which each of the data processing units is implemented using pipeline techniques and has a cache memory unit employing a store through strategy, the time required to prepare a write instruction operand address can be substantially shorter than the time required by the execution unit to prepare the associated write instruction operand. In order to utilize the time difference, apparatus is included in the execution cache unit for storing the write instruction operand address during the preparation of the associated write instruction operand. After storing the write instruction operand address, a next address is entered in an input register of the execution cache unit. When the newly entered address is associated with a read instruction, does not conflict with the write instruction operand address, and produces a "hit" signal when applied to the execution cache unit tag directory, the read instruction is processed by the execution unit.

Abstract: In a data processing system in which the execution unit is implemented to process aligned double word operands, apparatus and an associated method provide for the alingment of a double word operand that is stored across a double work boundary. The two double words each storing a word of the unaligned double word operand are identified and the attributes are compared with the ring number of the associated program. When the comparisons indicate that the two words of the non-aligned double word operand are available to the program, the two double word operands containing the non-aligned words of the double word operand, and the two non-aligned words are stored in a register in an aligned orientation for processing by the execution unit.

Abstract: A multiprocessor computer system includes a main memory and a plurality of central processing units (CPU's) which are connected to share main memory via a common bus network. Each CPU has instruction and data cache units, each organized on a page basis for complete operating compatibility with user processes. Each cache unit includes a number of content addressable memories (CAM's) and directly addressable memories (RAM's) organized to combine associative and direct mapping of data or instructions on a page basis. An input CAM in response to a CPU address provides a cache address which includes a page level number for identifying where all of the required information resides in the other memories for processing requests relating to the page. This organization permits the processing of either virtual or physical addresses with improved speed and reduced complexity and the ability to detect and eliminate both consistency and synonym problems.

Abstract: A least recently used replacement level generator is constructed to include n number of register stages connected in tandem. A comparison circuit associated with each stage except the last stage compare the contents of that stage with an input level value which is to be loaded into the input stage. In the absence of an identical comparison, each stage generates a shift enable signal which is passed on to the next succeeding stage. An identical comparison inhibits the generation of the shift enable signal. Therefore, when a clock signal is applied to the device, register stages, in the presence of a control signal, cause the input level to be loaded into the input stage while the level contents of the register stages are simultaneously shifted through successive stages including the register stage whose contents are identical to the input level under the control of the shift enable signal.

Abstract: What is disclosed is apparatus making up an arithmetic logic unit and utilizing a programmable read-only memory (PROM) to perform arithmetic functions for an associated processor. The PROM is used as a look-up table for computation results. Operands used to perform a mathematical computation make up an address to the PROM which is used to read out the computation result stored therein. Also stored in the PROM as part of each computation result are information bits indicating if the computation result is a valid answer. These bits are also read out and stored in flip-flops to indicate to the processor if the computation result is valid or invalid.

Abstract: A data processing system which includes a central processing unit coupled over a common bus with a plurality of input/output controllers (IOCs) and main memory includes apparatus which allows an IOC to signal the CPU to wait and retry the current I/O instruction. Other apparatus is provided which enables the CPU to continually retry the I/O instruction until the IOC accepts or rejects the I/O instruction and which further allows the CPU to suspend the retrying of the I/O instruction and to process interrupt requests and data transfer requests from any one of the plurality of IOCs. After processing the interrupt or data transfer request, system control is returned to retrying the I/O instruction.

Abstract: A computer system which facilitates the execution of nested subroutines and interrupts is disclosed. As each branch transfer within the program is executed by a control area logic, a microcommand initiates the transfer of the return address, which has been derived from the address in the present routine, to a first register of a push down stack. In addition, the microcommand also pushes down one level the contents of all of the registers in the stack containing previously stored return addresses. Thus, a sequential return to unfinished routines or subroutines is provided. When the subroutine or hardware interrupt service routine is completed, a code in the address field enables the return address of the previously branched from or interrupted routine to be retrieved from the first register in the push down stack and to provide it as the address of the next instruction to be executed.

Abstract: A hardware interrupt apparatus for assigning the microprogrammed control system to the highest priority hardware interrupt requesting service. In a microprogrammed control system having at least one hardware interrupt, the presence of a hardware interrupt request will cause the interruption of the currently executing microprogram at the end of the current microinstruction. The address of the next microinstruction in the interrupted microprogram is saved in a hardware interrupt return address register and the next microinstruction address is generated as a function of the particular hardware interrupt to be serviced. A microprogram dedicated to servicing the particular hardware interrupt is then entered at the hardware interrupt generated next microinstruction address. Logic is provided within each microinstruction to inhibit hardware interrupts.

Abstract: One or more common buses are provided for coupling a plurality of units in a data processing system for transfer of information therebetween. The central processing unit (CPU) allocates the one or more common buses to one of the requesting units as a function of request type and on which of one or more common buses the requesting unit is located. Bus requests are generated in a synchronous manner by use of a timing signal originating in the CPU which is connected in series between the one or more units on each of the one or more common buses.

Abstract: In a data processing system which includes a central processing unit and one or more main memory units comprised of semiconductor dynamic random access memory chips, logic is provided within the system to provide for the single stepping of the central processing unit clock thereby allowing for the execution of one CPU cycle. The system logic is organized such that the memory refresh command signals, which are normally generated by the CPU, are generated by the single step logic thereby maintaining the contents of the main memory modules. The logic of the overall data processing system is organized such that most transfers of information between the main memory, the CPU and I/O controllers, to which peripheral devices are connected, may take place in the single step mode of operation without the loss of information.

Abstract: In a data processing system which includes one or more common buses to which a plurality of input/output controllers are connected for the transfer of data, blocks of data may be transferred between main memory and an input/output controller (IOC) synchronously with operation of the central processor unit (CPU). Logic is provided for enabling one unit of data to be transferred during a Data Multiplex Control (DMC) data transfer operation in which the requesting IOC requests a DMC data transfer of the CPU and later provides the CPU with a channel number assigned to the requesting IOC. In order to allow a data entry operator inputting data via a peripheral device connected to an IOC the ability to correct errors, a backspace character is provided so that the operator can enter it to indicate to the system to ignore the preceding character.

Abstract: In a data processing system which includes a central processing unit (CPU) having one or more common buses to which one or more main memory units for storing program software instructions and program data are connected, logic is provided within the CPU for detecting an attempt to access a main memory location not contained in the one or more main memory units present in the data processing system. Logic is provided for detecting the attempt to access the nonexistent memory location for the case where the access was being done in the course of the CPU executing a software instruction or for the case of where the access was being done to transfer data between the main memory and an input/output controller connected to one of the one or more common buses.

Abstract: In a data processing system which includes a central processing unit (CPU), main memory and a plurality of input/output controllers (IOCs) connected to a common bus information can be transferred between the main memory and CPU and main memory and the IOCs. Logic is provided within the CPU to align a byte of data on the data lines of the common bus such that it can be taken from the data lines by the main memory and written into a multi byte word without further alignment. Logic is provided within the CPU to extract from a multi byte word of data read from main memory and appearing on the common bus data lines the appropriate byte of data and to align it on the common bus data lines such that an IOC may pass the data byte to a peripheral device without further alignment.

Abstract: In a data processing system which includes a central processing unit and one or more main memory units for storing program software instructions and program data, logic is provided within the CPU to signal the main memory units, comprised of semiconductor random access memory chips, that a memory refresh operation can be performed. The logic is organized such that the memory refresh operation signal may be given to the main memory units in parallel with and without detracting from other CPU operations. Further, logic is provided within the CPU to interrupt the CPU normal processing and perform a memory refresh operation if one has not been performed with a predetermined time period. Logic is provided within each main memory unit to accept the memory refresh signals from the CPU and to discard those memory refresh signals that would refresh the memory more frequently than required to retain the memory contents thus reducing main memory power consumption.

Abstract: In a data processing system which includes one or more common buses to which a plurality of input/output controllers are connected for the transfer of information, blocks of information may be transferred between main memory and an input/output controller (IOC) synchronously with operations of the central processor unit (CPU). Logic is provided for enabling one unit of the block of information to be transferred during a Data Multiplex Control (DMC) data transfer operation in which the requesting IOC requests a DMC data transfer of the CPU and provides the CPU with a channel number assigned to the requesting IOC. Means are provided within the CPU for determining: the direction of the data transfer, the address of the location of the unit of data to be transferred to/from the main memory, and the number of units of data remaining to be transferred between the main memory and the IOC.

Abstract: Multiple common buses are provided for coupling a plurality of units in a data processing system for the transfer of information therebetween. The central processing unit (CPU) allocates the multiple common buses to one of the units in response to bus requests received from various units desiring to use the common buses. Bus requests are generated in a synchronous manner by use of a timing signal originating in the CPU which is connected in series between the one or more units on each of the multiple common buses.

Abstract: In a data processing system which includes one or more common buses to which a plurality of input/output controllers are connected for the transfer of data, blocks of data may be transferred between main memory and an input/output controller (IOC) synchronously with operation of the central processing unit (CPU). Logic is provided for enabling one unit of data to be transferred during a Direct Memory Access (DMA) data transfer operation in which the requesting IOC requests a DMA data transfer of the CPU. Means are provided within the system for: resolving conflicting requests for the one or more common buses, the CPU to acknowledge the DMA request, the IOC to transfer the address of the location where the unit of data is to be written into main memory followed by the unit of data, or the IOC to transfer the address of the location in main memory from which the unit of data is to be read and then receive the unit of data read from main memory.

Abstract: In a data processing system which includes one or more common buses to which a plurality of input/output controllers are connected for the transfer of data, blocks of data may be transferred between main memory and an input/output controller (IOC) synchronously with operation of the central processor unit (CPU). Logic is provided for enabling one unit of data to be transferred during a Data Multiplex Control (DMC) data transfer operation in which the requesting IOC requests a DMC data transfer of the CPU and later provides the CPU with a channel number assigned to the requesting IOC. Means are provided within the system for: resolvng conflicting requests for the one or more common buses, the CPU to acknowledge the DMC request, identifying the requesting IOC to the CPU, accessing one unit of data from main memory or the IOC, and transferring the unit of data to the IOC or main memory.

Abstract: Interrupts generated within a data processor (internal interrupts) and an interrupt received from a peripheral device (external interrupts) coupled with the processor are prioritized and, unless suppressed, are coupled to generate an interrupt signal for use in addressing a routine for servicing the particular highest priority requesting internal or external interrupt. All further interrupts are suppressed during the time required to service the interrupt and, depending upon the type of interrupt, either the internal or external interrupt may be suppressed for one or two instruction times for debug purposes or under computer program control as required for a particular operation.

Abstract: Diagnostic testing of a central processor is provided in conjunction with a memory coupled with the processor without any requirement for an input device such as a tape or card reader. Local storage of a test program is provided in the processor which, under the control of a local control store, enables the transfer of the test program to the memory for execution. The central processor may thus be given an initial test to insure a basic performance level.