ZCOM System Header |
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The ZCOM System Header contains fixed information such as
the location and number of all the tables in the ZCOM sub-system,
and also the size of the buffer pool. For more detail, see the data
structure zheader_type in /opt/acc/include/zcom/zcomsys.h.
Node Entries |
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The Node Entries table contain information about the remote
ZCOM sub-systems that communicate with the local ZCOM sub-system.
Each entry contains statistics and control information for a node
and TCP/IP addressing information for the links to that node. For
more detail, see the data structure znode_type in /opt/acc/include/zcom/zcomsys.h.
ZLU Tables |
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The ZLU entries consist of information for the physical terminal
ZLUs plus the dynamically assignable ZLUs. The ZLU tables provide references
to various objects that can exist in the ZCOM subsystem, similar
to how file descriptors are used in HP-UX. ZLUs can refer to a network
communication endpoint or device such as an HDLC link or X.25 virtual
circuit (Terminal ZLU), or they can refer to an application (Program
ZLU). Each ZLU entries contains information about its owner, type,
and other operational information.
For more detail, see the data structure zlu_type in /opt/acc/include/zcom/zcomsys.h.
Logical Terminal Tables |
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The logical terminal tables contain information such as the
terminal type and location, and its owning ZLU number. A large area
of this table is reserved for use by the application programs. A
number of logical terminals may be linked to a single physical terminal;
for example, it may be used in any instance where a remote concentrator
handles a number of terminals. This means that there may be more
logical terminal tables than physical terminals. For more detail,
see the data structure zltt_type in /opt/acc/include/zcom/zcomsys.h.
Physical Terminal Tables |
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The physical terminal tables (one per terminal) include the
owning terminal ZLU number, and the high, low, and unacknowledged
queues, as well as the terminal status, transmit and receive buffer
counters, and terminal poll and select codes. For more detail, see
the data structure zptt_type in /opt/acc/include/zcom/zcomsys.h.
Interface Tables |
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There is one interface table per ACC interface card, containing information
such as the ACC interface number, scheduler event flags, interface
terminal count, the current backplane command, and data transfer
command, the high priority queue header and the low priority queue
header, and port configuration information. For more detail, see the
data structure zift_type in /opt/acc/include/zcom/zcomsys.h.
Response Records |
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A response record is assigned to each application request
that specifies the send-with-wait option (mode 8), for example,
zsend or zcntl. It is used as a temporary storage for the return
status when such request is completed. When the request originator
picks up the return status, the assigned record is returned to the
free pool and may be re-used. For more detail, see the data structure zrsp_type (response record) in /opt/acc/include/zcom/zcomsys.h.
Queues |
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The queue section of memory contains information on the free
buffers in the system, and also maintains pointers to the first
and last buffers attached to any queue, as well as a count of the
number of those buffers. For more detail, see the data structures zqhd_type (queue header) and zfqh_type (free queue header) in /opt/acc/include/zcom/zcomsys.h.
Buffer Pool |
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The buffer pool is a piece of fixed-size, contiguous memory.
Its total size is specified in the TTGEN configuration file. The
system allocates memory from this pool for ZCOM requests that require
buffering (for example, zsend),
and returns memory to this pool on completion. The memory allocated
is always large enough to hold the whole request in one contiguous
memory block. The first four words of each allocated buffer contains
pointer and linkage information, the data area contains the message
header and message data. The message header contains information
that relates to the messages, such as the message type, the destination
and source nodes and ZLUs. The buffers are chained together to form
a First-In-First-Out queue. Queue headers are used to keep track of
and manipulate the buffers. For more detail, see the data structures zbhd_type (buffer header) and zfbh_type (free buffer header) in /opt/acc/include/zcom/zcomsys.h.
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