HP Advanced Communications Controllers (ACC) manual Zcom Concepts

ZCOM Subsystem

ZCOM Concepts

level of priority. The Express Queue is used for extremely high-priority protocol dependent requests. The High-Priority Queue is used for high priority data and the Low-Priority Queue is used for low priority data.

When a message is generated by an application, the buffers involved are queued to the selected transmit queue and the ZCOM driver is notified. The driver is then responsible for handling the message. Messages on the express queue are sent before those on the high priority queue which are sent before those on the low priority queue.

Because the ZCOM Subsystem itself takes responsibility for the delivery of messages, the sending program is able to specify a number of options when it passes the message to the system. These options include:

•Continue execution whether the message is sent successfully or not.

•Continue execution but report any error status (status messages are queued to the ZLU of the calling program).

•Continue execution; a definite response will be queued to the program ZLU when the send has completed.

•Suspend execution until the send has completed (i.e., acknowledgment that the message was transmitted).

On completion, the message buffer may also be passed back to the sending application program if required.

Each message on the ZLU has a ‘type’ attribute so that the program reading the ZLU is able to differentiate between status messages, timeout messages and data messages from terminals or other programs.

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