Siemens SM2 monitoring system Manual Do Utilizador
U3585-J-Z125-8-76
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Glossary
channels
Channels are used for data interchange between the CPU, main memory and the
peripheral devices.
peripheral devices.
Multiplexer channel (generic term):
can handle several I/O operations simultaneously.
can handle several I/O operations simultaneously.
Byte multiplexer channel (BYMUX):
data is transferred in byte-interleaved fashion between main memory and several simul-
taneously active I/O devices. This type of channel is used to connect slow devices.
data is transferred in byte-interleaved fashion between main memory and several simul-
taneously active I/O devices. This type of channel is used to connect slow devices.
Block multiplexer channel (BLMUX):
data is transferred in block-interleaved fashion between main memory and several
simultaneously active I/O devices. This type of channel is used to connect fast devices
such as disk controllers.
data is transferred in block-interleaved fashion between main memory and several
simultaneously active I/O devices. This type of channel is used to connect fast devices
such as disk controllers.
counting of I/O operations and their duration
For SM2, an I/O operation is
–
any version of EXCP (EXCP, EXCPW, $EXCP, $EXCPW) or
–
an I/O request from the memory management system for paging (no SVC call)
addressed to the I/O control module. The I/O control module is the central system
component for handling physical I/O operations.
component for handling physical I/O operations.
The I/O control module normally processes the I/O request with one privileged
instruction (Start Device or Start Subchannel). For each instruction a termination
message is issued, upon which the I/O operation is counted.
instruction (Start Device or Start Subchannel). For each instruction a termination
message is issued, upon which the I/O operation is counted.
In rare cases (e.g. disk connected to a channel operated in selector mode), two SDV
instructions are issued. This is called "offline seek". The first SDV prepares the I/O
device and the second initiates the I/O operation proper. Only one I/O operation is
counted in this case too.
instructions are issued. This is called "offline seek". The first SDV prepares the I/O
device and the second initiates the I/O operation proper. Only one I/O operation is
counted in this case too.
The following particularities should be noted:
I/O requests which could not be started properly (SDV with condition code differing from
0) are ignored.
0) are ignored.
So-called SENSE SDVs, which are generally issued after an I/O request that resulted
in an error and serve to fetch additional diagnostic information, are only included in
report 100.
in an error and serve to fetch additional diagnostic information, are only included in
report 100.
In SDV fast release mode supported in some systems, a properly initiated I/O operation
can be rejected at a later time by a channel. The rejected SDVs are not counted.
can be rejected at a later time by a channel. The rejected SDVs are not counted.
In determining the duration of the I/O operation, the time between the SDV and the
termination message is always counted.
termination message is always counted.
An SDV rejected because of an error is ignored; this results in an increase in waiting
time for the device.
time for the device.