V4 DB Record Instance Syntax

The syntax used for record instances has to change in EPICS V4, since we now have to support structured data. While it would have been possible to modify the V3 syntax to allow for this, a complete redesign of the syntax has been done to help improve parsing, and to provide commonality between the syntax of a DB file and the string representation of structured data values passed through Channel Access.

Record Instances

A record instance loaded from a DB file has the following syntax:

# comment
recordType recordName = {
    fieldName = fieldValue;
    structFieldName = { fieldName = fieldValue; .. }
    structFieldName = { fieldValue, fieldValue, .. }
    structFieldName = { structFieldName = { .. } }
    arrayFieldName = { arrayValue, arrayValue, .. }
    arrayFieldName = type { arrayValue, arrayValue, .. }
    arrayFieldName = [size, ..] { { arrayValue, arrayValue, .. }, { .. } .. }
    arrayFieldName = type [size, ..] { arrayValue, arrayValue, .. }
    linkFieldName = linkName { linkValue }
    deviceFieldName = deviceName { deviceValue }
    info infoName = "infoString";
    add varFieldName = {
                 {fieldName,interfaceName,choiceName,{dataStructValue}},
                 ...
    }
    ...
}

where

recordType

The name of the record type

recordName

The name of the record instance.

Q: What restrictions will we place on record instance name? Can this contain non-ascii characters? That is will UTF-8 instance names be supported?

info name

provide info for field

fieldName

The field name.

type

One of the types bool,...,string. This is only specified if the record definition did not specify a type.

capacities

The capacities for an array. This can only be specified if the record definition did not define the number of dimensions or the capacities. It has the format:

capacity,...

The number of dimensions must agree with what record defined. For example if the record defined that array as array(<type>[]) then only one capacity can be specified. If a record defined array(<type>) than the record instance determines the number of dimensions and the capacities.

choiceName

This is for struct, link, and device fields. choiceName is a choice defined in a struct, link, or device definition.

fieldValue

The syntax depends on the field type. The details are described next..