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: Computer-based devices, whether initiators or targets, are assured access to a bus having a fixed priority arbitration scheme (such as a SCSI bus) by assigning to each initiator a “fair share” of the bus bandwidth. This share is defined as a number of bytes per a unit of time such as a time period. The shares together total a fraction of the total bus bandwidth, with a margin of bus bandwidth left unassigned. To prevent initiator starvation, each initiator monitors its bus requests to determine if it is being prevented by higher-priority initiators from using its assigned share of the bandwidth. If not, the initiator periodically pings each higher-priority initiator to indicate that it is not being starved. So long as a higher-priority initiator continues to receive pings from all lower-priority initiators, the higher-priority initiator can continue to use as much bandwidth as it needs.

Abstract: A host adapter integrated circuit has a dedicated circuit which detects an attempted access of a digital resource (for example, SCSI bus interface circuitry) from a system bus (for example, a PCI bus) and automatically generates a pause request signal to stop instruction execution of a sequencer of the host adapter integrated circuit. The sequencer stops executing instructions, the sequencer is decoupled from the digital resource, and the digital resource is coupled to the system bus. With the digital resource coupled to the system bus, the system bus access of the digital resource is completed. In some embodiments, a pause acknowledge signal is generated by bus transfer logic of the sequencer to indicate that the digital resource can be accessed from the system bus. This pause acknowledge signal is used to generate a ready signal onto the system bus.

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: At least two clusters of CPUs are present in a multiprocessor computer system. Each CPU cluster has a given number of CPUs, each CPU having an associated ID such as an ID number. An additional ID number, not associated with a CPU in the same cluster, is associated with the opposite CPU cluster that appears to the original cluster as a "phantom" processor. A round-robin bus arbitration scheme allows ordered ownership of a common bus within a first cluster until the ID reaches the "phantom" processor, at which time bus ownership passes to a CPU in the second cluster. This arrangement is preferably symmetric, so that when a CPU from the first cluster requests ownership of the bus, it is granted bus ownership by virtue of the first cluster's appearance to the second cluster as a "phantom" CPU.