If the CRW indicates that a subchannel caused the machine check, the operating system examines the error recovery code in the CRW. If the CRW indicates that the subchannel is available, the channel subsystem has recovered from a previous malfunction. I/O functions in progress and presentation of status by the device have not been affected. No program action is required.
If the CRW indicates that the subchannel is installed parameter initialized, the operating system determines if the device associated with the subchannel is still valid. If it is, the operating system enables the subchannel again. If, however, the device related to the subchannel is not valid, the operating system marks the device as unusable and issues message IOS151I.