Abstract: A data transfer control apparatus is disclosed for controlling conflict of data transfer on a data bus connected to a microprocessor through a bridge circuit. The bridge circuit includes a monitoring unit. When an execution instruction for MPC transfer is issued during DMA transfer, the monitoring unit measures a time period over which the data bus is to be occupied with the MPC transfer. When the PCI bus is to be occupied with the MPC transfer for a predetermined time period, the monitoring unit does not suspend the DMA transfer but performs the MPC transfer after the completion of the DMA transfer.

Abstract: A bus arbitration apparatus includes a storage, a priority order determiner, and an arbitrator. The storage stores a plurality of selection signals for specifying a priority order against a number N of requests. The priority order determiner causes the storage to output one of the plurality of selection signals in a predetermined sequence in response to a demand for arbitration. The arbitrator performs an arbitration operation based on the priority order against the number N of requests specified by one of the plurality of selection signals which is output from the storage.

Abstract: In a method of and a system for managing reselection of an initiator by a target on a SCSI bus, the target attempts to secure control of the bus for a first reselection cycle to reselect the initiator. If the target fails to secure control of the bus for the first reselection cycle and the target is selected by the initiator for a selection cycle, the target processes the selection cycle. However, concurrently with processing the selection cycle, substantially immediately after the bus becomes free, and before the target completes processing the selection cycle, the target attempts to secure control of the bus for a second reselection cycle to reselect the initiator.

Abstract: The present invention provides a means for preventing execution of a transaction such as main storage access from obstruction by bus competition with low-speed IO access and improving the bus occupation efficiency. The present invention includes a first bus, a second bus, a plurality of modules connected to both buses, a bus conversion means for performing protocol conversion of information between both buses, a bus arbiter for arbitrating a bus occupation right request of a bus master, and a storage means for storing access data up to a predetermined amount when the access destination is a predetermined module. Each bus master outputs access destination information and when the bus arbiter judges that one of the bus masters issues a bus occupation right request when it performs an access operation, the bus arbiter refers to the access destination information and the data storage status of the storage means and decides whether or not to give a bus occupation right to the bus master.

Abstract: The invention concerns an arbitration scheme for permitting access to the bus of a computer. The arbitration scheme has the ability to control and reduce the delay experienced by any device by monitoring the queue length of the device and using information concerning the device, such as device rate, phase, data transfer size and queue length. Specifically, the arbiter prevents periodic accessing devices, such as audio and video samplers, from being delayed or interrupted for long periods of time once they have begun accessing the bus.

Abstract: In the context of a bus-mastering system, a device selector selects the device to control the bus by assigning “combined” priority values to the devices and selecting the device with the highest combined-priority value. The combined-priority values include relatively high-significance device-specific values and relatively low-significance arbitrary-rank values. At any given time, no two devices share the same arbitrary-rank values, and thus cannot share combined-priority values. Thus, there are no unresolved selections due to equal priorities. In accordance with the present invention, the arbitrary-rank values are varied in a round-robin fashion to minimize the bias inherent in conventional schemes using a priority encoder. This makes the device selection process conform better to the device-specific values, which are presumable selected to optimize system performance.

Abstract: A data storage system includes a plurality of control/data buses. A memory section is coupled to the plurality of control/data buses. The memory section includes a memory and a plurality of control logic sections interconnected through an arbitration bus. Each one of the control logic sections is coupled between a corresponding one of the control/data buses and the memory. Each one of such control logic sections includes a control logic for controlling transfer of data between the memory and the one of the plurality of control/data buses coupled to said one of the logic sections. The control logic is adapted to produce a control/data bus request for the one of the control/data buses coupled thereto and is adapted to effect the transfer in response to a control/data bus grant fed to the control logic. Each one of the control logic sections also includes a bus arbitration section coupled to the arbitration bus.

Abstract: One embodiment of the present invention provides an apparatus that selectively encodes bus grant lines to reduce I/O pin requirements. This apparatus includes a semiconductor chip with bus arbitration circuit. A number of grant lines emanate from the bus arbitration circuit. An encoder circuit encodes the grant lines into a smaller number of encoded grant lines. A selector circuit selects outputs from between the encoded grant lines and a first subset of grant lines. These outputs pass through output pins off of the semiconductor chip. During a first mode of operation, the first subset of grant lines is driven through the plurality of output pins. During a second mode of operation, the encoded grant lines are driven through the output pins. A variation on the above embodiment includes a number of bus request lines, which are divided into a first subset and a second subset. The first subset of request lines feeds through a number of input pins into the bus arbitration circuit.

Abstract: One embodiment of the present invention provides a method for selectively encoding bus grant lines to reduce I/O pin requirements. The method includes receiving a number of grant lines emanating from a bus arbitration circuit and encoding the grant lines into a smaller number of encoded grant lines. The method selects outputs from between the encoded grant lines and a first subset of the grant lines. These outputs are driven off of a semiconductor chip through a number of output pins. During a first mode of operation, the first subset of grant lines is selected to be driven through the output pins. During a second mode of operation, the encoded grant lines are selected to driven through the output pins. In a variation on the above embodiment, the method additionally receives a number of bus request lines. These request lines are divided into a first subset and a second subset. The first subset of request lines is received through a number of input pins from off of the semiconductor chip.

Abstract: Data communications device and method for arbitrating access to a system memory of the communications device via a peripheral component interconnect (PCI) bus in a network interface having a memory management unit for managing transmit data transfers from the system memory to a transmit buffer memory, and receive data transfers from a receive buffer memory to the system memory. The memory management unit includes an arbitration block having an arbiter state machine, which receives requests for access to the PCI bus in order to provide the transmission and reception of data, descriptors and status information. The arbiter state machine grants the PCI bus access to a request having a higher priority in accordance with a preset priority scheme.

Abstract: A method of limiting, in a digital processor, low-priority utilization of a resource in favor of high-priority utilization of the resource comprises determining a value predictive of high-priority utilization of the resource. Low-priority utilization of the resource is inhibited if the determined predictive value is greater than a threshold. On the other hand, if the predictive value is less than or equal to the threshold, then low-priority utilization of the resource is allowed. In a preferred embodiment, the predictive value is derived by counting the number of actual high-priority utilizations of the resource out of the last N opportunities in which the resource could have been utilized for a high-priority need. Preferably, recent utilizations are given more weight than others. In a preferred embodiment, the resource comprises one of main memory, instruction cache memory, or data cache memory.

Abstract: A method is described for controlling data transfer operations between a main memory and other devices in a computer system. Data transfer request signals and associated latency identification values are received. Each of the latency identification values corresponds with a maximum time interval in which to service the respective data transfer request. The latency identification values are periodically modified and compared to indicate the current highest priority request. In the event that service of a particular requested data transfer operation must be provided imminently, priority override functionality is provided. In this way, those devices having particular latency requirements can be provided with timely access to the main memory, and need not have separately dedicated memory or buffers.

Abstract: A computer system includes an adaptive memory arbiter for prioritizing memory access requests, including a self-adjusting, programmable request-priority ranking system. The memory arbiter adapts during every arbitration cycle, reducing the priority of any request which wins memory arbitration. Thus, a memory request initially holding a low priority ranking may gradually advance in priority until that request wins memory arbitration. Such a scheme prevents lower-priority devices from becoming “memory-starved.” Because some types of memory requests (such as refresh requests and memory reads) inherently require faster memory access than other requests (such as memory writes), the adaptive memory arbiter additionally integrates a nonadjustable priority structure into the adaptive ranking system which guarantees faster service to the most urgent requests.

Abstract: A queued arbitration mechanism transfers all queued processor bus requests to a centralized system controller/arbiter in a descriptive and pipelined manner. Transferring these descriptive and pipelined bus requests to the system controller allows the system controller to optimize the system bus utilization via prioritization of all of the requested bus operations and pipelining appropriate bus grants. Intelligent bus request information is transferred to the system controller via encoding and serialization techniques.

Abstract: A bus controller for a CCD digital still camera arbitrates competing requests by multiple microcontrollers for a shared memory. One of the microcontrollers is designated to have a higher priority than the other microcontroller(s). In the case of competing requests, while one microcontroller is granted access to the memory, the other microcontroller performs other processing, and polls a memory status register to determine when the memory is available. Since the waiting processor performs other operations, as opposed to idling, the efficiency of the microcontroller is improved.

Abstract: A system and method for transferring data in a multiprocessor architecture capable of supporting multiple processors. The system comprises a priority assignor that provides a dynamic priority to input/output unit (IOU), D-cache and I-cache devices requests as a function of an intrinsic priority assigned to each device and a plurality of factors including the existence of a row match between a requested address and a previously serviced request, the number of times a device has been denied service and the number of times a device has been serviced without interruption. The system also includes a tracker to keep track of the number of times each of the factors occurs and a priority changer to change the priority of the devices as a function of the intrinsic priority and the number.

Abstract: A computer system, bus interface unit, and method are provided to allocate requests to a shared bus within the computer system. The bus interface unit includes an arbiter which employs a multi-level, round-robin arbitration protocol. Configuration registers are programmed during boot-up of the computer system by assigning a subset of peripheral devices, bus agents, requesters, or bus masters to either a high priority ring or a low priority ring, if two levels of arbitration are used. The status of a low priority device can be elevated to equal priority with a high priority device by assigning the low priority device to a high priority port within the high priority ring if certain circumstances occur. Namely, if data transfers to or from the low priority device are terminated, then the low priority device will be promoted to a high priority device so that it need not wait until after the all high priority device requests have been polled.

Abstract: Where a plurality of ordered transactions are received for data transfers on a pipelined bus, each transaction in the series is initiated before all prospective retry responses to the preceding ordered transactions may be asserted. The address responses to all preceding ordered transfers are then monitored in connection with performance of the newly initiated transfer. If a retry response to any preceding ordered transaction is asserted, a self-initiated retry response for all subsequent transactions, including the newly initiated transfer, is also asserted. The system-retried transactions and all succeeding, ordered transactions are immediately reattempted. The overlapping performance of the ordered transfers reduces the latency of non-retried transfers, achieving performance comparable to non-ordered transactions.

Abstract: A method and apparatus is provided for assuring balanced servicing of interrupts among devices at the same interrupt level in a daisy-chain architected bus, such as the VME bus, by detecting that a second device on the same level as a first device is having an interrupt serviced, and responsive thereto raising the interrupt level of the first device.

Abstract: A bus protocol for a split bus (50, 60) where each device (10, 20, 30) coupled to the bus has an age-based queue (12, 24, 34) of pending transactions. Queues are updated as transactions are executed. A central arbiter (40) has a copy of each device's queue (44). A priority transaction is determined from among all the queues in the arbiter. A data transaction index (DTI) is broadcast during the data tenure to all devices indicating the position in the queue of the next transaction. The index allows out-of-order data transfers without the provision of a static tag during the address tenure. Queues maintain a history of pending transactions. In one embodiment, each device receives a separate data bus grant (DBG), allowing a single provision of the index to both a source and a sink device.

Abstract: A method of limiting, in a digital processor, low-priority utilization of a resource in favor of high-priority utilization of the resource comprises determining a value predictive of high-priority utilization of the resource. Low-priority utilization of the resource is inhibited if the determined predictive value is greater than a threshold. On the other hand, if the predictive value is less than or equal to the threshold, then low-priority utilization of the resource is allowed. In a preferred embodiment, the predictive value is derived by counting the number of actual high-priority utilizations of the resource out of the last N opportunities in which the resource could have been utilized for a high-priority need. Preferably, recent utilizations are given more weight than others. In a preferred embodiment, the resource comprises one of main memory, instruction cache memory, or data cache memory.

Abstract: According to the present invention, a system for reordering commands to achieve an optimal command sequence based on a target response restriction is disclosed. A data queue coupled to a command queue is arranged to store a time indicating when the data transfer will appear on the data bus between the controller for an already issued request to the target device as well as arranged to store the burst bit and the read/write bit (r/w). The system also includes a collision detector coupled to the data queue and the command queue arranged to detect the possible collisions on the data bus between the issued command that is stored in the command queue and already issued commands that are stored in the data queue. A queues and link controller is coupled to the collision detector and the data queue and the command queue and is arranged to store and reorder commands to be issued wherein the controller calculates the new issue time of commands as well as a time when the data appears on the data bus.

Abstract: A method and apparatus for throttling high priority memory accesses. An apparatus of the present invention includes an arbiter circuit and a throttling circuit. The arbiter circuit is coupled to receive first and second types of memory access commands and has a preference for the first type of memory access commands. The throttling circuit is coupled to the arbiter and can at least temporarily reduce the preference for the memory access commands of the first type.

Abstract: A bus transfers information including isochronous and asynchronous data between a first and a second integrated circuit. The bus guarantees a minimum bandwidth to isochronous data and also tries to minimize latency for isochronous data. The bus transfers data in asynchronous priority mode during a first portion of a first time period, wherein asynchronous data is transferred preferentially over isochronous data. Transfers over the bus selectably switch to isochronous priority mode for a second portion of the first time period in order to guarantee transfer of a predetermined amount of isochronous data during the first time period, thus guaranteeing the minimum bandwidth to isochronous data.

Abstract: The operation of any desired number of initially unidentified slave stations in a communications system is possible. An identification procedure with a subsequent address assignment is carried out by a master station M, in that all the slave stations simultaneously output bit by bit, via open-drain output circuits OC, individual identification codes ID which are stored in them.

Abstract: A priority decision circuit decides priorities of a plurality of slots on the basis of access frequencies or the like. In conformity with these priorities, a bus mapping circuit performs mapping allowing a slot having a higher priority to be connected to the upper hierarchical bus whereas it performs mapping allowing a slot having a lower priority to be connected to the lower hierarchical bus.

Abstract: An arbiter connects a plurality of devices to a bus. The arbiter determines priority among the devices based on minimum access intervals associated with the devices and timers which keep track of the elapsed time since each device last had access to the bus. The timers can be configured to either count up from zero to the minimum access interval of each device or count down from the minimum access interval of each device to zero. The arbiter can also adjust the minimum access intervals of the various devices based upon factors such as the amount of data required by the device, the amount of data most recently received by the device and the transfer rate of the device. The arbiter thus optimizes bus usage while minimizing the likelihood of a given device not functioning based on an ability to access the bus due to contention with other devices.

Abstract: A register associated with the architected logic queue of a memory-coherent device within a multiprocessor system contains a flag set whenever an architected operation—one which might affect the storage hierarchy as perceived by other devices within the system—is posted in the snoop queue of a remote snooping device. The flag remains set and is reset only when a synchronization instruction (such as the “sync” instruction supported by the PowerPC™ family of devices) is received from a local processor. The state of the flag thus provides historical information regarding architected operations which may be pending in other devices within the system after being snooped from the system bus. This historical information is utilized to determine whether a synchronization operation should be presented on the system bus, allowing unnecessary synchronization operations to be filtered and additional system bus cycles made available for other purposes.

Abstract: An arbitration and task switching technique in a real-time multiprocessor data processing system (20) having a common bus (32) and a segmented shared memory (30), where fullness of memory segments of the shared memory (30) is used as a measurement for arbitration and task switching priorities. A bus request mechanism in each of the processors dynamically calculates normalized priority values based on relative needs across the system (20). The normalized priority calculation is based on monitoring the fullness of memory segments of the shared memory (30) associated with each processor (24, 26, 28) of the system (20). Using this normalized priority calculation, the bus access order and bus bandwidth are optimally allocated according to tasks executed by the processors (24, 26, 28). Also, the normalized priority calculation and a preprogrammed threshold is used to control task switching in the multi-processor system (20).

Abstract: A computer system avoids livelock conditions on a computer bus coupled to plural bus masters. In response to receiving a transaction request from a first bus master across the computer bus, a bus controller transmits a retry command to the first bus master if the bus controller is unable to execute the transaction request. A livelock condition is avoided by preventing transaction requests from any of the bus masters, other than the first bus master, from being processed until after the first bus master re-submits the transaction request. The bus controller may prevent execution of the transaction request from the other bus masters by transmitting retry commands to all bus masters that submit transaction requests after the transaction request from the first bus master is received and before the first bus master re-submits the transaction request.

Abstract: A recording apparatus is disclosed that, in use, is connected with a host apparatus, receives recording information from the host apparatus by direct memory access ("DMA") and can print received recording information by using a recording head. A first memory access circuit receives recording information from the host apparatus by DMA. A second memory access circuit supplies received recording information to the recording head with a timing appropriate for recording, using DMA. A priority circuit controls the respective priorities assigned to various types of DMA to ensure that all types of DMA demands can be accommodated within an acceptable length of time.

Abstract: A system and method for high speed transferring of bus operations which are preferably strictly ordered in a processing system is provided. A system and method in accordance with the present invention comprises issuing a plurality of bus operation requests by a processor and determining if a first response has been received by the same processor indicating that one of the plurality of bus operation requests should be reissued. Then, if the first response is received, the processor provides a second response indicating that at least another of the issued bus operation requests should be reissued.

Abstract: A data processing system (20) schedules the allocation of a common bus (26), used by multiple service requesters (32). The system (20) creates a plurality of service request levels (44) and assigns each service requester (32) to one of the plurality of request levels (44). Services of the common bus (26) are provided to all service requesters (32) assigned to a first service request level (44) for each instance of providing service to one of the service requesters (32) assigned to a second service request level (44). The method then again provides services of the common bus (26) to all service requesters (32) assigned to the first service request level (44) for a single instance of providing service to one of the second level requesters (32).

Abstract: A scheme for arbitrating access to a data bus shared among a plurality of competing sources is provided. Each competing source is assigned an adjustable priority weighting value (PWV) which is initially set to an initial value based on the bandwidth requirements of the competing source. During arbitration, the PWVs of those competing sources requesting access to the bus are compared, and the competing source with the smallest PWV is granted access. The PWV of the competing source which was granted access to the bus is reset to its initial value and the PWV of each competing source which requested, but was denied, access is reduced by one for subsequent comparisons. The arbitration scheme of the present invention is further applied to two-level arbitration. Each competing source is classified into a competing source group, and the requests from the grouped competing sources are processed by first level arbitration. First level arbitration passes one competing source for each group to a second level arbiter.

Abstract: The present invention comprises a computer system with a reconfigurable bus priority arbitration system. The computer system of the present invention includes a master device, a slave device, an arbiter and a reconfigurable bus priority arbitration system, all coupled to a bus. The reconfigurable arbitration system determines said master device's relative priority for bus accesses and is capable of implementing a plurality of linked arbitration priority schemes.

Abstract: An improved data processing system and in particular an improved data processing system that more effectively manages a shared resource within a data processing system. More specifically, a method and apparatus for managing access to a shared resource between a plurality of devices simultaneously requesting access to the shared resource. The present invention implements a design that combines a priority configuration and a shifting sequential configuration. The access is controlled by an arbiter that determines access to the shared resource by granting first, to priority devices and then to the highest priority shifting sequential device requesting access within one clock cycle of a device terminating its request for access to the shared resource.

Abstract: An arbiter uses a history based bus arbitration scheme to more fairly allocate a shared resource among multiple devices. The arbiter uses a history queue to dynamically update the priorities of the devices using the shared resource, and makes the grant decision in a single calculation using the combination of the history queue and requests from bidding devices. The priority for granting master to each device is dynamically modified so that the least recently serviced requestor will be granted the shared resource. A hidden arbitration scheme provides more fair history based resource allocation. A bus retry scheme demotes priority for processing devices that are assigned bus master but do not perform bus operations within a predetermined number of clock cycles. The arbiter also prevents bus grants during hot swap operations.

Abstract: A round robin arbitration circuit arbitrating N requests has a register storing one of N values, a priority encoder selecting one of N priority patterns according to the value in the register and assigning priorities to the requests based on the selected priority pattern, thereby conducting arbitration between the requests, a circuit updating the value in the register among the N values in a predetermined order synchronously with the arbitration, and a circuit updating the value in the register among the N values in the predetermined order at regular intervals that are asynchronous with the arbitration. At the regular intervals that are asynchronous with the arbitration, a jump is made in the predetermined updating order of the values to be set in the register. Accordingly, even if live-lock occurs, it will be solved when such a jump is made to make the number of priority patterns disagree with the number of requests issued in a loop.

Abstract: A queued arbitration mechanism transfers all queued processor bus requests to a centralized system controller/arbiter in a descriptive and pipelined manner. Transferring these descriptive and pipelined bus requests to the system controller allows the system controller to optimize the system bus utilization via prioritization of all of the requested bus operations and pipelining appropriate bus grants. Intelligent bus request information is transferred to the system controller via encoding and serialization techniques.

Abstract: A system and method for dynamic priority conflict resolution in a multi-processor computer system having shared memory resources wherein a predetermined priority level for each input port is maintained by each output port. When a conflict for a particular output port occurs, the priority levels of the conflicting inputs are evaluated and access is initially granted to the highest priority input. Once this initial access is granted, the priority level of the "winning" input is then changed to the lowest priority level and the priority of all of the other inputs is increased by one. Inputs not requiring access to a particular output port over a relatively long period of time will resultantly have their priority incremented to the highest level and remain there. If multiple inputs have been incremented to the highest priority, or another form of priority conflict occurs, the input may then default back to its original predetermined priority.

Abstract: In a computer including two buses, a main memory, a write back cache, and a peripheral device, a method and apparatus for providing an inter-bus buffer to support successive main memory accesses from the peripheral device is disclosed. The buffer is included in a bridge device for interfacing the two computer buses and controlling when the peripheral device may access the main memory. When the peripheral device attempts to read data from the main memory that is duplicated in the cache and that has become stale, the bridge device initiates a write back operation to update specific data portions of the main memory corresponding to the read request. The bridge device uses look-ahead techniques such as bursting or pipelining to streamline the data coming from the cache to the main memory and to the peripheral device.

Abstract: A data processing apparatus serves as I/O units coupled to information processes apparatuses such as computers. The data processing apparatus decodes encrypted data and performs processing according to message data. The data processing apparatus includes a data processing circuit performing decoding processing and message processing according to message data, a data buffer accessible from both the data processing circuit and the information processing apparatus, a data buffer monitor circuit monitoring states of read/write of the data to the data buffer, and an access control circuit controlling an access from the information processing apparatus to the data buffer.

Abstract: A method and system for controlling access to a shared resource in a data processing system are described. According to the method, a number of requests for access to the resource are generated by a number of requesters that share the resource. Each of the requesters is assigned a current priority, at least the highest current priority being determined substantially randomly with respect to previous priorities of the requestors. In response to the current priorities of the requestors, a request for access to the resource is granted. In one embodiment, a requester corresponding to a granted request is signaled that its request has been granted, and a requester corresponding to a rejected request is signaled that its request was not granted.

Abstract: One aspect of the invention relates to a method for arbitrating simultaneous bus requests in a multiprocessor system having a plurality of devices which are coupled to a shared bus. In one version of the invention, the method includes the steps of receiving a plurality of bus requests from the devices; determining a device having the highest priority; determining whether the device having the highest priority is requesting the bus; granting bus access to the device having the highest priority if the device having the highest priority is requesting the bus; sequentially searching, beginning from the device logically adjacent to the device having the highest priority, for a next requesting device, and granting bus access to the next requesting device if the device having the highest priority is not requesting the bus; and assigning the highest priority to the device logically adjacent to the next requesting device.

Abstract: A method and system for controlling access to a shared resource in a data processing system are described. According to the method, a number of requests for access to the resource are generated by a number of requesters that share the resource. Each of the requesters is associated with a priority weight that indicates a probability that the associated requester will be assigned a highest current priority. Each requester is then assigned a current priority that is determined substantially randomly with respect to previous priorities of the requesters. In response to the current priorities of the requesters, a request for access to the resource is granted. In one embodiment, a requester corresponding to a granted request is signaled that its request has been granted, and a requester corresponding to a rejected request is signaled that its request was not granted.