Processing a variable length device command word at a control unit in an I/O processing system

• US 7,840,717 B2
• Filed: 02/14/2008
• Issued: 11/23/2010
• Est. Priority Date: 02/14/2008
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Kalos, Matthew J., Huang, Catherine C., Flanagan, John R., Sittmann, Gustav E., Njoku, Ugochukwu C., Casper, Daniel F., Riedy, Dale F.
• Primary Examiner(s): Patel; Niketa I
• Assistant Examiner(s): Unelus; Ernest
• Application Number:
  US12/030,939
• Publication Number:
  US 20090210559A1
• Time in Patent Office: 1,013 Days
• Field of Search: 710/5, 710/20, 710/21, 710/24, 710/36, 710/45, 710/100, 710/107, 710/62
• US Class Current: 710/5
• CPC Class Codes: G06F 13/126 and has means for transferring I/O instructions and statuses between control unit and main processor

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.

Claims

1. A computer program product 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 comprising:

a tangible storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method comprising;

receiving a DCW at the control unit from the I/O subsystem via a transport command control block (TCCB) that includes a transport command area (TCA) header, a TCA where one or more DCWs are located, and a TCA trailer, the DCW specifying one or more I/O operations and including a command, a control data count, and control data having a varying length specified by the control data count;

extracting the control data in response to the control data count; and

executing the command in response to the extracted control data to perform the specified one or more I/O operations.

2. The computer program product of claim 1, wherein the DCW further includes a customer data count specifying an amount of customer data associated with the DCW.

3. The computer program product of claim 2 wherein the customer data count has a value greater than zero and the method further comprises receiving customer data from the I/O subsystem.

4. The computer program product of claim 2 wherein the customer data count has a value greater than zero and the method further comprises transmitting the customer data to the I/O subsystem.

5. The computer program product of claim 1 wherein the method further comprises completing the I/O operations and transmitting a completion message to the I/O subsystem in response to the completing.

6. The computer program product of claim 1 wherein the I/O subsystem is a channel subsystem.

7. An apparatus for processing a variable length DCW in an I/O processing system, the apparatus comprising:

a control unit for communicating with an I/O subsystem, the control unit configured to perform a method comprising;

receiving a DCW specifying one or more I/O operations at the control unit from the I/O subsystem via a transport command control block (TCCB) that includes a transport command area (TCA) header, a TCA where one or more DCWs are located, and a TCA trailer, the DCW including a command, a control data count, and control data having a varying length specified by the control data count;

extracting the control data in response to the control data count; and

executing the command in response to the extracted control data to perform the specified one or more I/O operations.

8. The apparatus of claim 7, wherein the DCW further includes a customer data count specifying an amount of customer data associated with the DCW.

9. The apparatus of claim 8 wherein the customer data count has a value greater than zero and the method further comprises receiving the customer data from the I/O subsystem.

10. The apparatus of claim 8 wherein the customer data count has a value greater than zero and the method further comprises transmitting the customer data to the I/O subsystem.

11. The apparatus of claim 7 wherein the method further comprises completing the I/O operations and transmitting a completion message to the I/O subsystem in response to completing.

12. A method for processing a variable length DCW at a control unit configured for communication with an input/output (I/O) subsystem in an I/O processing system, the method comprising:

receiving a DCW specifying one or more I/O operations at the control unit from the host computer system via a transport command control block (TCCB) that includes a transport command area (TCA) header, a TCA where one or more DCWs are located, and a TCA trailer, the DCW including a command, a control data count, and control data having a varying length specified by the control data count;

extracting the control data in response to the control data count; and

executing the command in response to the extracted control data to perform the specified one or more I/O operations.

13. The method of claim 12, wherein the DCW further includes a customer data count specifying an amount of customer data associated with the DCW.

14. The method of claim 13 wherein the customer data count has a value greater than zero and the method further comprises receiving the customer data from the I/O subsystem.

15. The method of claim 13 wherein the customer data count has a value greater than zero and the method further comprises transmitting the customer data to the I/O subsystem.

16. The method of claim 12 further comprising completing the I/O operations and transmitting a completion message to the I/O subsystem in response to the completing.