Abstract: A computer program product, an apparatus, and a method for processing communications between a control unit and a channel subsystem in an input/output processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method.

Abstract: A bi-directional and full duplex facility for permitting both the IO processor and the Channel to write CCA messages on their respective queues at the same time. IOP messages to the channel are stored on the TO_CHN queue and Channel messages to the IOP on the TO_IOP queue. CCA Queues replace hardware CCAs due to increasing transmission capabilities of current IO processors and Channel processors. Even though the mechanism is similar, the present invention provides some benefits in the use of signaling. The IOP does not have to signal the Channel each time it puts something on its outbound queue. Each queue contains multiple slots. This allows the IOP and Channel to write multiple messages on the targeted queue without encountering a CCA busy signal. The actual queues are now structured in hardware system memory.

Abstract: A computer program product, apparatus, and method for processing a transport control channel program with chain linked branching in an I/O processing system are provided. The method includes receiving a command message at a control unit from an I/O subsystem to perform an I/O operation. The method further includes reading a chain linked flag in the command message indicating that a subsequent command message for the I/O operation follows the command message. The method also includes reading a serialization flag in the command message requesting that device status be returned to the I/O subsystem in order to select the subsequent command message. The method additionally includes executing one or more commands in the command message, and transmitting the device status to the I/O subsystem in response to executing the one or more commands in combination with the serialization flag.

Abstract: A method, apparatus, and computer program product for processing a chain linked transport control channel program in an I/O processing system is provided. The method includes receiving a first command message at a control unit specifying a first predetermined sequence number for performing a first set of one or more commands as part of an I/O operation. The method further includes receiving a second command message specifying a second predetermined sequence number for performing a second set of one or more commands as part of the I/O operation. The method also includes comparing the sequence numbers to a next expected predetermined sequence number to determine an order of performing the commands. The method additionally includes executing the commands in the determined order to perform the I/O operation.

Abstract: A method, apparatus, and computer program product for processing a chained-pair linked transport control channel program in an I/O processing system is provided. The method includes receiving a first command message at a control unit specifying that a device command word (DCW) list is encoded in a data message associated with the first command message as part of the chained-pair linked transport control channel program. The method further includes receiving a second command message chained-pair linked to the first command message, the second command message specifying data attributes associated with the DCW list. The method additionally includes extracting the DCW list from the data message in response to receiving the data message, and executing the DCW list.

Abstract: A system, method and storage medium for providing redundant I/O access between a plurality of interconnected processor nodes and I/O resources. The method includes determining whether a primary path between the interconnected processor nodes and the I/O resources is operational, where the primary path includes a first processor node and a primary multiplexer. If the primary path is operational, the transactions are routed via the primary path. If the primary path is not operational, the transactions are routed between the interconnected processor nodes and the I/O resources via an alternate path that includes a second processor node and an alternate multiplexer.

Abstract: A computer program product, an apparatus, and a method for limiting a number of open exchanges at a channel subsystem of an I/O processing system using data from a control unit. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method that includes sending a command message to the control unit, and receiving a transport response information unit message in response. The method further includes extracting a maximum control unit exchange parameter from the transport response information unit message, and determining a limit value for a maximum number of open exchanges between the channel subsystem and the control unit as a function of the extracted maximum control unit exchange parameter. The method additionally includes applying the limit value to prevent opening of a new exchange.

Abstract: A computer program product, apparatus, and method for handling exception condition feedback at a channel subsystem of an I/O processing system using data from a control unit are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes sending a command message to the control unit, and receiving a response message in response to the command message. The response message includes exception condition feedback identifying a termination reason code in response to unsuccessful execution of at least one command in the command message. The method also includes interrupting a CPU in the I/O processing system, and reporting status associated with the exception condition feedback to the CPU in an interrupt response block.

Abstract: A computer program product, apparatus, and method are provided for determining a state of an input/output (I/O) operation in an I/O processing system. A request from a channel subsystem is received at a control unit for performing the I/O operation. After a predetermined amount of time passes without the I/O operation completing, an interrogation request is received from the channel subsystem at the control unit for determining the state of the I/O operation. A response is sent from the control unit to the channel subsystem indicating the state of the I/O operation in response to the interrogation request. The response also includes information regarding a state of an I/O device executing the I/O operation and information indicating a state of the control unit controlling the I/O device executing the I/O operation.

Abstract: A computer program product, an apparatus, and a method for processing communications between a target and an initiator an input/output processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes: sending a message from the initiator to the target, the message requesting suspension of input/output operations between the initiator and the target for a period of time, the period of time being defined by the message; responsive to the message, suspending input/output operation messages for the period of time; performing a system change comprising at least one of: at least one update, a computer program installation, a recovery, and a change in operating parameters; and initiating new input/output operations after at least one of: expiration of the period of time and initiation of new input/output operations by the initiator.

Abstract: A computer program product, apparatus, and method for providing exception condition feedback at a control unit to a channel subsystem in an I/O processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a command message at the control unit from the channel subsystem, and detecting an exception condition in response to unsuccessful execution of at least one command in the command message. The method further includes identifying a termination reason code associated with the exception condition, writing the termination reason code to a response message, and sending the response message to the channel subsystem.

Abstract: A computer program product, apparatus and method for processing a variable length device command word (DCW) at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a DCW at the control unit from the I/O subsystem. The DCW specifies one or more I/O operations and includes a command, a control data count, and control data having a varying length specified by the control data count. The control data is extracted in response to the control data count. The command is then executed in response to the extracted control data to perform the specified one or more I/O operations.

Abstract: A computer program product, an apparatus, and a method for reducing reserved device access contention at a control unit in communication with a plurality of operating systems via one or more channels are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method that includes receiving a command message at the control unit from a first operating system, including an I/O operation command for a device. A device busy indicator is received, indicating that a second operating system has reserved the device. The command message is queued on a device busy queue in response to the device busy indicator. The control unit monitors for a device end indicator. The device busy queue is serviced to perform the I/O operation command in response to the device end indicator.

Abstract: A computer program product, an apparatus, and a method for processing communications between a control unit and a channel subsystem in an input/output processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes: sending a command from the channel subsystem to the control unit to initiate an input/output operation; setting a time period for completion of the operation; and responsive to the operation not completing within the time period, sending a message to determine whether the control unit has an exchange open for the command.

Abstract: A computer program product, an apparatus, and a method for processing communications between a control unit and a channel subsystem in an input/output processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method.

Abstract: A computer program product, apparatus, and method for determining extended capability of a channel path in an I/O processing system are provided. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a request to provide a channel path description for a channel path, where the channel path includes a channel coupled to a control unit. The method further includes outputting the channel path description for the channel path in response to the request. The channel path description includes a descriptor indicating that the channel path supports a link protocol for commanding an I/O operation, and an extension support indicator specifying whether the channel path supports an extension to the link protocol.

Abstract: An article of manufacture, an apparatus, and a method for determining an extended measurement word at a channel subsystem of an I/O processing system using data from a control unit are provided. The article of manufacture includes at least one computer usable medium having computer readable program code logic. The computer readable program code logic performs a method including sending a command message to the control unit, and receiving a transport response information unit message at the channel subsystem in response to sending the command message to the control unit. The computer readable program code logic additionally extracts a plurality of time values from the transport response information unit message as calculated by the control unit, calculates an extended measurement word as a function of the time values, and writes the extended measurement word to computer readable memory in the I/O processing system.

Abstract: Articles of manufacture, apparatuses, and methods for processing communications between a control unit and a channel subsystem in an input/output processing system are disclosed. Embodiments of the invention include an article of manufacture including at least one computer usable medium having computer readable program code logic to processing communications between a control unit and a channel subsystem in an input/output processing system. The computer readable program code logic performs a method including: sending a message in a first mode from the control unit to the channel subsystem; receiving a command in a second mode from the channel subsystem at the control unit; determining whether the command is responsive to the message; and responsive to the command being not responsive to the message, determining whether to perform one of i) executing the command and ii) terminating the command.

Abstract: An article of manufacture, apparatus, and a method for facilitating input/output (I/O) processing for an I/O operation at a host computer system configured for communication with a control unit. The method includes the host computer system obtaining a transport command word (TCW) for an I/O operation having both input and output data. The TCW specifies a location of the output data and a location for storing the input data. The host computer system forwards the I/O operation to the control unit for execution. The host computer system gathers the output data responsive to the location of the output data specified by the TCW, and then forwards the output data to the control unit for use in the execution of the I/O operation. The host computer system receives the input data from the control unit and stores the input data at the location specified by the TCW.

Abstract: Systems, methods and computer program products for providing indirect data addressing at an I/O subsystem of an I/O processing system. The computer program product includes a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method includes receiving a control word for an I/O operation. The control word includes an indirect data address for data associated with the I/O operation. The indirect data address includes a starting location of a list of storage addresses that collectively specify the data, the list spans two or more non-contiguous storage locations. Data is gathered responsive to the list. The gathered data is transmitted to a control unit in the I/O processing system.