Browse Prior Art Database

Multipath Controls

IP.com Disclosure Number: IPCOM000043790D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 3 page(s) / 61K

Publishing Venue

IBM

Related People

Fickle, DM: AUTHOR [+2]

Abstract

A multipath accessing system, such as to a peripheral data storage system, has a separate controller for each access path. Each controller includes controls having a microprocessor and register sets such that each of the peripheral resources being accessed is assigned to one path in the accessing system irrespective of its busy state. One of the paths is designated as a primary path. All resources are assigned initially to the primary path. When the primary path gets busy, all of the resources not currently being used or performing a freestanding operation are transferred to another path. The other path then can access any of the resources for the accessing system each time the primary becomes nonbusy. All of the nonbusy resources assigned to the other paths are then reassigned to the primary access path.

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Multipath Controls

A multipath accessing system, such as to a peripheral data storage system, has a separate controller for each access path. Each controller includes controls having a microprocessor and register sets such that each of the peripheral resources being accessed is assigned to one path in the accessing system irrespective of its busy state. One of the paths is designated as a primary path. All resources are assigned initially to the primary path. When the primary path gets busy, all of the resources not currently being used or performing a freestanding operation are transferred to another path. The other path then can access any of the resources for the accessing system each time the primary becomes nonbusy. All of the nonbusy resources assigned to the other paths are then reassigned to the primary access path. Accordingly, the resources being accessed are assigned to one path at all times and to a primary path when not busy, provided the primary path is also not busy. Electronic circuitry required to arbitrate accessing between path controls which share resources is shown diagrammatically in the figure. The path controls are identical in construction. The only difference occurs at initial program load wherein the microprocessor of the respective path controls sets the connect latches, one latch for each resource, in the primary path control "A" and resets the connect latches in the secondary path control "B". This action is indicated in the drawing by the letter P for path control "A" and by the letter "A" for the path control "B". Two classes of commands are receivable from the accessing system. One class is path control specific, and the other class is resource specific. The path control accepts a path control specific command if the address matches that of the path control. On the other hand, either path control will accept a resource specific command if it is appropriately connected to the resource desired to be accessed and if it currently has control of the address or commanded resource. To assign which path control has access rights to each resource, each path control has two control latches for the device: a busy latch and a connect latch. The connect latch gates the path control signals to the resource interface and also determines which resource address the respective path control responds to. The busy latches respectively indicate when a device is executing a command and cannot be switched to the other path control.

For transferring control of the peripheral resource from one path control to the other path control requires the switch box between the path controls which share accessing rights to the resources for the sw...