z/OS DFSMSdfp Advanced Services
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Event Control Block (ECB) Fields

z/OS DFSMSdfp Advanced Services
SC23-6861-01

Define an event control block (ECB) as a 4-byte area on a word boundary. When the channel program has been completed, the system places a completion code containing status information into the ECB (Figure 1). Before examining this information, test for the setting of the complete bit. If the complete bit is not on, and your problem program cannot perform other useful operations, issue a WAIT or EVENTS macro instruction that specifies the ECB. Do not construct a program loop to test for the complete bit.

The ECB is mapped by the IHAECB macro.

You do not have to set any particular values in the ECB before issuing EXCP or EXCPVR because the system clears it.

Figure 1. Event Control Block after Posting of Completion Code
Event Control Block after Posting of Completion Code
Wait bit
One in this position indicates that the WAIT or EVENTS macro instruction has been issued, but the channel program has not been completed.
Complete bit
A one in this position indicates that the channel program has been completed. If it has not been completed, a zero bit is in this position.
Completion code
This code, which includes the wait and complete bits, might be one of the following hexadecimal expressions. If an appendage posts the ECB, it might use other 4-byte codes in which the first two bits are 01. Refer to Start-I/O Appendage and Channel-End Appendage.

The system sets these codes in IOBECBCC and IEDBCOD before posting the ECB.

Code
Meaning
41
Permanent I/O error
42
Extent error (DASD only). Either IOBSEEK lies outside the extents described by the DEB or the channel program attempted execution outside the current extent.
44
An error occurred after the previous I/O request to the device was posted complete. The appendages and (if allowed to execute) the ERP have determined that this is a permanent error. The I/O request is terminated with the permanent error. The CSW contents and sense data in the IOB do not apply to the attempted operation. They apply to the previous operation attempted for any data set on the device. You can reissue the EXCP macro instruction to restart the channel program.
45
A program check or machine check occurred in IOS while processing the I/O request.
48
The channel program was purged.
4B
An error occurred during tape repositioning that was requested by the tape ERP.
4F
Error recovery routines were entered following a direct access error but are unable to read the home address or record 0.
51
Simulated error status. The appendages and, if allowed to execute, the ERP have determined that this is a permanent error. The I/O request is terminated with the permanent error. This code indicates that the device is in a permanent error state, boxed, or not connected. The code can indicate also that a missing interrupt was detected and that the I/O operation was terminated as a result of recovery operations by the missing interrupt handler.

This completion code appears only in the IEDB, if one was provided. It is translated to a 41 completion code prior to updating the ECB and IOBECBCC.

74
Simulated error status. This code is set as a result of attempting to start an I/O operation to a device that is in a permanent error state, boxed, or not connected. This code is also set if a missing interrupt was detected and the I/O operation was terminated as a result of recovery operations by the missing interrupt handler. The system has set this code temporarily in IOBECBCC and IEDB to invoke the ERP, if allowed to execute, and the appendages to determine if the error is permanent or correctable. If the error is determined to be permanent the system will change the value to 51. The system does not set the 74 code in the ECB.
7F
Normal I/O completion, but does not appear in the ECB.
Reason code byte
Reason code for the completion code.
Code
Meaning
0E
A zHPF channel program was specified but the device does not support zHPF. This reason code appears with completion code 41.
10
A zHPF channel program was specified, but the I/O request was terminated because a capability needed by the I/O request is not supported by the processor, device, or software. This reason code is presented if an EXCPVR request is issued when the processor and device do not support the zHPF incorrect length facility. This reason code appears with completion code 41.

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