ZCOM Tables and Data Structures

Physical Terminal Tables

This queue contains the high priority transmit requests waiting to be sent. It also contains the terminal configuration (zcntl) requests. The data on this queue is processed only after all express transmit data has been processed. When a message has been transferred to the card, the buffers are moved to the unacknowledged transmit buffer queue. Once the buffer has been acknowledged as sent or flushed by the card it is removed from the unacknowledged queue and returned to the sending program (if requested by the program). Note that requests on this queue are subject to the unacknowledged and port transmit limits.

PTTXLB - Pointer to next PTT on low priority list linkage

As for PTTXLA above, except that the linkage pertains to the low priority transmit queue.

PTTXQB - Low priority transmit buffer queue

The low priority queue is operated in a similar manner to the high priority queue. Data on this queue is processed only after all express and high priority data has been processed. Note that requests on this queue are subject to the unacknowledged and port transmit limits.

PTTXQC - Unacknowledged transmit buffer queue

This queue contains the buffers from PTTXQA/B after they have been transferred to the interface card, and until they have been acknowledged as sent (or aborted) by the Mux interface card.

PENDG_TXREQ - Next request of $DATA in unack’d transmit queue

This field is used internally by the ZCOM subsystem.

PTPZLK - ZLU of next PTT on this port

Contains the ZLU number of the next terminal which is on the same Mux interface and port as this terminal. These ZLU numbers form a circular list of terminals on the same port. Field PTLIST forms the same circular list, but contains the physical terminal table memory address.

PTDRST - Terminal status

The terminal status is maintained by the driver in this field. The status change requests from application programs are updated in this field after they are successfully passed to the interface card. The driver uses this value to reset the terminal status on the Mux interface after a powerfail or reset.

Chapter 3

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