Timeout considerations

Some control units and I/O devices have valid operational conditions that exceed the 30-second I/O interface timeout function limit. If timeout is active when such a condition occurs, the channel terminates the I/O request and generates an interface-control-check interruption, even though no malfunction exists. For example:

• A timeout might occur during a read operation to a magnetic tape unit if the tape being read is blank. While the magnetic tape unit searches for a data byte or the end-of-tape mark, it might exceed the 30-second timeout function limit.
• A channel-to-channel adapter between two CPCs might time out if one system attempts to communicate with the other system while the other CPC is in a stopped state.

When timeout is active, the channel might terminate an I/O request and generate an interface-control-check interruption even though no control unit or I/O device malfunction has occurred.