National Instruments NI-VXI

Chapter 3 Software Overview

NI-VXI User Manual 3-22 © National Instruments Corporation

WSSnoResp ()

WSSnoResp sets the WR bit so that it is ready to accept any further

Word Serial commands. The WSScmd interrupt handler should call

WSSnoResp after processing a Word Serial command (it calls

WSSsendResp for a Word Serial query, which requires a response).

WSSrd (buf, count, modevalue)

WSSrd is the buffer read function. WSSrd receives a specified number

of bytes from a VXI message-based Commander device and places the

bytes into a memory buffer, using the VXIbus Byte Transfer Protocol.

The process involves setting the DIR and WR bits on the local CPU

Response register and building a buffer out of data bytes received via a

series of Byte Available (BAV) Word Serial commands. When WSSrd

reaches the specified count or an END bit, or an error occurs, it calls

the WSSrd interrupt handler with the status of the call. It clears the DIR

bit before setting the WR on the last byte of transfer.

WSSsendResp (response)

WSSsendResp responds to a Word Serial Protocol query from a VXI

message-based Commander device. The WSScmd interrupt handler calls

this function to respond to a Word Serial query. If a previous response

has not been read yet, a WSSsendResp call generates a Multiple Query

Error (MQE). Otherwise, it writes a response value to the Data Low

to accept any further Word Serial commands.

WSSwrt (buf, count, modevalue)

WSSwrt sends a specified number of bytes to a VXI message-based

Commander device, using the VXIbus Byte Transfer Protocol. The

process involves setting the DOR and WR bits in the local Response

Serial commands. When the data output completes or an error occurs,

WSSwrt calls its interrupt handler with the status of the call. Before

responding to the last byte of the write, it clears DOR to prevent

another BREQ from being sent before the application is able to handle

the BREQ properly.