ACC Programmer's Reference Guide

48 Chapter3
ZCOM Tables and Data Structures
ZCOM Header Structure
HUNACK - M aximum number of unacknowledged Tx buffers pending
onaterminalZLU
Upper limit of the total size (in bytes) of all unacknowledged transmit
messages to a terminal ZLU. If this limit has been reached, any further
write requests to the terminal ZLU will be queued up in the terminal
table, but will not processed by the driver immediately. The driver will
resume processing of queued transmit requests when the Mux card
acknowledges the completion of a previously issued transmit request for
this terminal ZLU. This mechanism is used to prevent a few (or only one)
terminal from consuming all of the transmit bufferson the Mux interface
card. This field is initialized from the Unack-Limit parameter in the
TTGEN configuration file. The unacknowledged queue limit may be
changed dynamically by calling the zsetql() routine.
HMAXTX - Maximum number of Tx buffers pending on a terminal ZLU
Limit of transmit buffers pending on a t erminal. W hen this limit is
reached, the program doing write requests to the terminal will be
suspended until some of the pending transmit requests are sent.
Together with the limit imposed by HUNACK, this protects the ZCOM
system buffers from excessive usage due to dead terminals (or other kind
of device).
HIPLIM - Default IFT port TX limit (bytes)
This field contains the limit (in bytes) of all unacknowledged transmit
messages to terminal ZLUs belonging to the same port of a 2/8-port Mux
card. Each port on the card has approximately 24,480 bytes of buffer
space available for both internal use and transmit requests. If the DAM
issues a tra nsmit request to the Mux card and the Mux card does not
have enough free buffers to hold the request data, the Mux will reject the
requestwithan“out of buffers” error. The DAM will retry t he request
after an unacknowledged transmit request completes. This field is used
to minimize the number of retries (and thereby increase overall
performance) by imposing a limit on the size of unacknowledged
transmit requests. This value is configured through the Port-Limit
parameter in the TTGEN configuration file and i s used to initialize the
individual port limits iplimit[] kept in the interface table (zift_type).