International Business Machines Corporation

John W McCullough

Roy L Hoffman

Frank G Soltis

William G Kempke

Richard T Turner

Joseph R Mathis

William G Kulpa

Ballard J Blevins

An improvement in a bus converter that provides a bus to bus address translation function permitting access from an I/O device connected on the I/O bus to a system bus and system memory, where the bus converter includes a circuit connected to the I/O bus to partition I/O addresses received from the I/O bus into a lower order field and a high order field and connected to a circuit to receive DMA ID's from the I/O bus to combine this DMA ID with the high order field to form a first combined address. The first combined address is input to a memory which provides corresponding control field and prefix field data. An address formatter is further included that is connected to receive the control field and prefix field data from the memory and further connected to receive the low order address field. The address formatter forms a second combined address from the prefix field, control field and lower order address field. This second combined address is then provided to a system bus to permit access to the system bus.

Bus to bus converter using a RAM for multiple address mapping

A method and apparatus are provided to enable interruption of list processing operations in a computer system and to enable restart from the point of interruption. A mechanism, at a predetermined point of the list processing operation, operates to recognize occurrences of interrupting events. If any such events are present, a mechanism saves the status of the list processing operation, saves the identification of the task associated with instruction executing the list processing operation and locks the list or queue. After the interrupt is handled, a mechanism restores status, and unlocks the list or queue only when the identified task is active again and the instruction which had been executing the list processing operation is again executing.

Process and apparatus for interrupting and restarting sequential

Improved task handling apparatus for a computer system where the task dispatcher is selectively operable under instruction control for performing task queue selection and where the intertask communication mechanism can return a task dispatching element (TDE) to a non-prime task dispatching queue (TDQ) as well as to the prime TDQ. Whenever a TDE is returned to the prime TDQ, the task dispatcher makes a pre-emptive task switch. Also, if there are no task dispatching elements on the current non-prime TDQ, the task dispatcher switches to dispatch TDE's from the prime TDQ.

Task handling apparatus

Task handling apparatus in a computer system is structured to be common to system control tasks, user tasks and I/O tasks. Although the task handling apparatus contains a task priority structure, all tasks are handled in the same manner, and there are no fixed interrupt levels for I/O tasks. There are N levels of priority, and N is variable. Each task is a server for a functional request. Task dispatching elements (TDE's) are enqueued in priority sequence on a task dispatching queue (TDQ). A task dispatcher functions to dispatch the highest priority TDE on the TDQ, if any, and to perform task switching. Intertask communication is accomplished by send message, send count, receive message and receive count mechanisms, and is coupled with task synchronization. Task synchronization is achieved by dequeueing and enqueueing TDE's on the TDQ. An active task becomes inactive dispatchable when a higher priority TDE is enqueued on the TDQ by send message or send count mechanisms. The active task becomes inactive waiting when a receive message or receive count is not satisfied. An inactive dispatchable task becomes the active task when it becomes the highest priority enqueued TDE on the TDQ by the receive message or receive count mechanisms. An inactive waiting task becomes either the active task or an inactive dispatchable task after being enqueued on the TDQ by the send message or send count mechanisms, depending upon whether it is the highest or other than the highest priority TDE on the TDQ.

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Rochester, MN, United States of America

John W McCullough