1 Readdata 10 Bytes
2 TIC to10 3 Unused 4 Search on 9 + 2
5 Etc.
6ISAK vord
7I I 8 Unused I I I 9 Data Area for Readdata 10 Seek Head on 9
11 TIC to4 The interruption return address in the IOBLOK is set to D!KUNTIS. D!KUNTIS restores the CCWs to their original format fro. the seven
doublevord extensions,moves the 10 bytes of data fro. 8+7 into virtual
storage (at C+7), and releases the block. Nor.alI/O handling is resu.ed by DMKVIO and DMKUNT. I/O COMPONENT STATES The I/O components represented by the control blocks described in "Real I/O Control Blocks" are in one of four states and the state is indicated by the flag bits in the block status byte. If the component is not
disabled, it is either busy, scheduled, or available.
If the disabled bit is on, the component has been taken offlineby the operator or the system and is at least te.porarily unavailable. A request to use a disabled component causes the IOBLOK to be stacked with an indication of condition code 3 on the 510 and the real 510 is not performed. An I/O unit is busy if it is transferring data (in the case of a
channel or control unit), or if it is in physical aotion (in the case of
a device). If anI/O unit is busy, the IOBLOK for the request is queued
fro. the control block representing thatI/O unit. An I/O unit is scheduled if it is not busy but viII become busy after
a higher-level component in the subchannel pathbecomes available and an
operation is started. For example, if a request is .ade to read fro. a
tape drive and the drive and control unit are available, but the channel
is busy, theIOBLOI for that request is queued fro. the RCHBLOK for the
busy channel and theRCUBLOK and RDEVBLOK of the drive and control unit
are .arked as scheduled. Future requests to that drive are queued fro.
theBDEVBLOK for the scheduled dp.vice. When the channel co.pletes the
operation, the next pending operation is dequeued and started; the
scheduled control unit and device are then .arked as busy.
TheIOBLOKs for various I/O requests indicate the status of that
requestby a co.bination of the status bits in the IOBLOK and the queue CP Introduction 1-89
2 TIC to
5 Etc.
6
7
11 TIC to
doublevord extensions,
storage (at C+7), and releases the block. Nor.al
disabled, it is either busy, scheduled, or available.
If the disabled bit is on, the component has been taken offline
channel or control unit), or if it is in physical aotion (in the case of
a device). If an
fro. the control block representing that
a higher-level component in the subchannel path
operation is started. For example, if a request is .ade to read fro. a
tape drive and the drive and control unit are available, but the channel
is busy, the
busy channel and the
are .arked as scheduled. Future requests to that drive are queued fro.
the
operation, the next pending operation is dequeued and started; the
scheduled control unit and device are then .arked as busy.
The
request