IBM 4300 Manual page 239

signaled to conclude the operation the next time it
requests or offers a byte of data. Program check
causes command chaining to be suppressed.
Protection Check
Protection check occurs when the channel attempts
a storage access that is prohibited by key-controlled
storage protection. Protection applies to the
fetching of CCWs and output data, and to the
storing of input data. Storage accesses associated
with each channel program are performed using the
sub channel key provided in the CAW associated
with that channel program. For details, see the
section "Key-Controlled Protection" in Chapter 3,
"Storage."
Protection check also occurs when it is detected
that the channel has attempted to access a CCW or
data from a page that is in the disconnected state.
For details, see the section "Page States" in
Chapter 3, "Storage."
When protection check occurs during the
fetching of a CCW that specifies the initiation of
an I/O operation, the operation is not initiated.
When protection check is detected after the device
has been started, the device is signaled to conclude
the operation the next time it requests or offers a
byte of data. Protection check causes command
chaining to be suppressed:
Channel-Data Check
Channel-data check indicates that a machine error
has been detected in the information transferred to
or from storage during an I/O operation, or that a
parity error has been detected on the data on
bus-in during an input operation. This information
includes the data read or written, as well as the
information transferred as data during a sense or
control operation. The error may have been
detected in the channel, in storage, or on the path
between the two. Channel-data check may be
indicated for data with an invalid checking-block
code in storage when the data is referred. to by the
channel but the data does not participate in the
operation.
Whenever a parity error on I/O input data is
indicated by means of channel-data check, the
channel forces correct parity on all data received
from the I/O device, and all data placed in storage
has valid checking-block code. When, on an input
operation, the channel attempts to store less than a
complete checking block, and when invalid
checking-block code is detected on the checking
block in storage, the contents of the location
remain unchanged with invalid checking-block
12-54 IBM 4300 Processors Principles of Operation
code. On an output operation, whenever a
channel-data check is indicated, all bytes that came
from a checking block with invalid checking-block
code have been transmitted with parity errors.
Channel-data check causes command chaining to
be suppressed but does not affect the execution of
the current operation. Data transfer proceeds to
normal completion, if possible, and an interruption
condition is generated when the device presents
channel end. A logout may be performed,
depending on the channel. Accordingly, the
detection of the error may affect the state of the
channel and the device.
Channel-Control Check
Channel-control check is caused by machine
malfunction affecting channel controls. It may be
caused by invalid checking-block code on CCW
and data addresses and invalid checking-block code
on the contents of the CCW. Channel-control
check may also include those channel-detected
errors associated with data transfer that are not
indicated as channel-data check, as well as those
I/O interface errors detected by the channel that
are not indicated as interface-control check. Errors
responsible for channel-control check may cause
the contents of the CSW to be invalid and
conflicting. The CSW as generated by the channel
has valid checking-block code.
Detection of channel-control check causes the
current operation, if any, to be immediately
concluded.
Channel-control check is set whenever CSW bit
5, logout pending, is set to one.
In some situations, machine malfunctions
affecting channel control may instead be reported
as an external-damage or system-damage
machine-check condition.
Interface-Control Check
Interface-control check indicates that an invalid
signal has been received by the channel when
communicating with a control unit or device. This
check is detected by the channel and usually
indicates malfunctioning of an I/O device. It can
be due to the following:
1. The address or status byte received from a
device has invalid parity.
2. A device responded with an address other than
the address specified by the channel during
initiation of an operation.
3. During command chaining the device appeared
not operational.
4. A signal from a device occurred at an invalid
time or had invalid duration.