ZCOM Tables and Data Structures

ZCOM Header Structure

file. The default limit may be overridden during a zopen() by specifying a non-zero value in the limit parameter. The program ZLU queue limit may be changed dynamically by calling the zsetql() routine.

HUNACK - Maximum number of unacknowledged Tx buffers pending on a terminal ZLU

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 buffers on the Mux interface card. This field is initialized from the Unack-Limitparameter 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 terminal. When 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 transmit 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 request with an “out of buffers” error. The DAM will retry the 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-Limitparameter in the TTGEN configuration file and is used to initialize the individual port limits iplimit[] kept in the interface table (zift_type).

Chapter 3

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