Ivi_SetAttrWriteCallbackViSession
Usage
ViStatus Ivi_SetAttrWriteCallbackViSession(ViSession vi, ViAttr attributeID, WriteAttrViSession_CallbackPtr writeCallback);
Purpose
This function sets the write callback function for a ViSession attribute. The IVI engine calls the write callback function when you specify a new value for the attribute and the cache value is invalid or is not equal to the new value.
If you do not want the IVI engine to invoke a write callback, specify VI_NULL for the Write Callback parameter.
You can set the write callback function when you create the attribute with Ivi_AddAttributeViSession.
Parameters
| Name | Type | Description | ||
|---|---|---|---|---|
| vi | ViSession |
The ViSession handle that you obtain from Ivi_SpecificDriverNew. The handle identifies a particular IVI session. |
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| attributeID | ViAttr |
Pass the ID of an attribute for this parameter. The include file for a specific instrument driver defines constant names for all of the user-accessible attributes that apply to the driver. This includes attributes that the IVI engine defines, attributes that the instrument class defines, and attributes that are specific to the particular instrument. Each defined constant name begins with PREFIX_ATTR_, where PREFIX is the specific instrument prefix. For each IVI engine attribute, the specific driver include file uses the same constant name that appears in ivi.h, except that the specific instrument prefix replaces the IVI prefix. For example, ivi.h defines IVI_ATTR_CACHE, and the Fluke 45 include file, fl45.h, defines the following constant name: #define FL45_ATTR_CACHE IVI_ATTR_CACHE For each instrument class attribute, the specific driver include file uses the same constant name that appears in the instrument class include file, except that the specific instrument prefix replaces the class prefix. For example, the DMM class include file, ividmm.h, defines IVIDMM_ATTR_RANGE, and fl45.h defines the following constant name: #define FL45_ATTR_RANGE IVIDMM_ATTR_RANGE For each specific instrument attribute, the specific driver include file defines a constant name and assigns a value that is an offset from IVI_SPECIFIC_PUBLIC_ATTR_BASE. For example, fl45.h defines the following constant name: #define FL45_ATTR_HOLD_THRESHOLD \ (IVI_SPECIFIC_PUBLIC_ATTR_BASE + 3L) For each attribute that is private to an instrument driver, the instrument driver source file defines a constant name and assigns a value that is an offset from IVI_SPECIFIC_PRIVATE_ATTR_BASE. For example, hp34401a.c defines the following constant name: #define HP34401A_ATTR_TRIGGER_TYPE \ (IVI_SPECIFIC_PRIVATE_ATTR_BASE + 1L) |
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| writeCallback | WriteAttrViSession_CallbackPtr |
Specify the write callback function you want the IVI engine to invoke when you set the attribute to a new value. You must define the write callback function in the source code for the specific instrument driver. The function must have the following prototype: ViStatus _VI_FUNC Callback(ViSession vi,ViSession io,
If you do not want to use a write callback function, pass VI_NULL. |
Return Value
Contains the status code that the function call returns. IVI engine functions can return error and warning values from several sets of status codes. Some status codes are unique to the IVI engine. Other status codes are the same codes that VISA Library functions return. Still others are error or warning values that functions in specific instrument drivers return. Each set of status codes has its own numeric range.
Regardless of the source of the status code, 0 always indicates success, a positive value indicates a warning, and a negative value indicates an error.