NonStop S-Series Server Description Manual (G06.24+)

Input/Output Operations

HP NonStop S-Series Server Description Manual—520331-003

10-20

Application of Communications Queues

Figure 10-10 illustrates the typical application of communications work queues. Note

that the direction of the arrows indicates which entity (controller or communications

monitor) writes to a given queue, and which entity reads from that queue. In the

following discussion, the terms “out” and “in” refer to the perspective of the processor—

command information going out from the processor or coming in to the processor.

Three groupings of queues are shown. The first group is a single pair (out and in). The

out-direction queue provides a means for a communications monitor to transfer

command information to a particular controller (for example to provide addressing

information to the controller regarding all the other queues available to that controller).

The in-direction queue provides a means for the controller to signify to the monitor

such things as completion of an earlier request, or to supply new information (such as

ServerNet addresses allocated in the controller).

The next two groups (one of which is shown detailed) are representative of what could

be numerous other groupings of queues. Typically, these queues are allocated on the

basis of two pairs for each resource (a resource being typically one communications

line or one ATM virtual circuit). One pair of the group (out and in) is used for

transmission (TX) operations, usually commands in the out direction and completion

information in the in direction. The other pair of the group (out and in) is used for

receiving (RX) operations, usually to provide buffer addresses to the controller in the

out direction and indication of new controller actions in the in direction.

The figure paraphrases typical exchanges that occur between the monitor and the

controller. A TX command typically informs the controller that a message exists in a

data buffer at a certain ServerNet address in the processor and that it needs to go to a

certain communications line. After the controller has read the command and acted

upon it, it sends a TX completion message to the monitor that essentially says that the

controller has pulled the message from the data buffer and successfully transferred it

to the specified communications line.

An RX buffer command from the monitor typically gives the controller a selection of

data buffer addresses to use whenever it needs to send a message to the monitor.

When the controller actually does need to send a message to the monitor, it first goes

ahead and sends the message with ServerNet DMA transfers and then, after the

message has been sent, informs the monitor which buffer it used by supplying the

ServerNet address in an RX indication command.