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has been transferred to or from the storage area
designated by the CCW. No interruption
conditions are generated at the subchannel, and
the subchannel is available for a new I/O
operation. If device end is not indicated, the
device remains busy, and a subsequent
device-end condition is generated.
4. The I/O device is interruption-pending, or the
control unit is interruption-pending for the
addressed device. The CSW unit-status field
contains one in the busy-bit position, identifies
the interruption condition, and may contain
other bits provided by the device or control
unit. The interruption condition is cleared.
The I/O operation is not initiated. The
channel-status field indicates any errors
detected by the channel, and the PCI bit is one
if PCI was specified in the first CCW.
5. The I/O device or the control unit is executing
a previously initiated operation, or the control
unit is interruption-pending for a device other
than the one addressed. The CSW unit-status
field contains one in the busy-bit position or, if
the control unit is busy, the busy and
status-modifier bits are ones. The I/O
operation is not initiated. The channel-status
field indicates any errors detected by the
channel, and the PCI bit is one if specified in
the first CCW.
6. The I/O device or control unit detected an
equipment or programming error during the
initiation, or the addressed device is not ready.
The CSW identifies the error. The channel-end
and busy bits are zeros, unless the device was
busy, in which case the busy bit, as well as any
bits causing interruption conditions, are ones.
The interruption conditions indicated in the
CSW have been cleared at the device. The I/O
operation is not initiated. No interruption
conditions are generated at the I/O device or
sub channel. The PCI bit in the CSW is one if
PCI was specified in the first CCW.
When the SIO or SIOF function cannot be
executed because of a pending logout which affects
the operational capability of the channel or
subchannel, a full CSW is stored. The fields in the
CSW are all set to zeros, with the exception of the
12-22
IBM 4300 Processors Principles of Operation
logout-pending bit and the channel""control-check
bit, which are set to ones. No channel logout
occurs in this case.
When the SIOF function causes condition code 0
to be set and subsequently a situation is
encountered which would have caused a condition
code 1 to be set had the function been SIO, a
deferred -condition -code-l I/O-interruption
condition is generated. When the SIOF function
causes condition code 0 to be set and,
subsequently, it is determined that the device is not
operational, a deferred-condition-code-3 1/0-
interruption condition is generated. In both of the
above cases, in the resulting I/O interruption, a full
CSW is stored, and the deferred condition code
appears in the CSW.
On the byte-multiplexer channel, both the SIO
and SIOF functions cause the addressed device to
be selected and the operation to be initiated only
after the channel has serviced all outstanding
requests for data transfer for previously initiated
operations.
Program Exceptions:
Privileged Operation
Resulting Condition Code:
o
I/O operation initiated and channel
proceeding with its execution
1
CSW stored
2
Channel or subchannel busy
3
Not operational
The condition code set by START I/O and
START I/O FAST RELEASE for all possible
states of the I/O system is shown in the figure
"Condition Codes Set by START I/O and START
I/O FAST RELEASE." See the section "States of
the Input/Output System" in this chapter for a
detailed definition of the A, I, W, and N states.
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