ACC Utilities Reference Guide

Chapter 2 33
TTGEN - ZCOM System Table Generator
Memory Image File Overview
Queues
The queue section o f 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
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), a nd 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 buffersarechained together
to form a First-In-First-Out queue. Queue headers are used to k eep track
of a nd 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.