The permissive record is for communication between a server and a client. An example would be a sequence program server and an operator interface client. By using multiple permissive records a sequence program can communicate its current state to the client.
Note this record is deprecated and may be removed in a future EPICS release.
The record-specific fields are described below, grouped by functionality.
The permissive record has the standard fields for specifying under what circumstances the record will be processed. These fields are listed in "Scan Fields". In addition, "Scanning Specification" explains how these fields are used. Since the permissive record supports no direct interfaces to hardware, its SCAN field cannot be
The client and server communicate through the VAL and watchdog flag (WFLG) fields. At initialization, both fields are set equal to 0, which means OFF. The server sets WFLG equal to ON when it is ready to accept a request. The client monitors WFLG and when WFLG equals 1, the client-server action is performed (a private matter between server and client).
When WFLG is off--when the server is busy--the client program may turn the VAL field from OFF to ON. After the server finishes its task, it will notice that VAL is ON and will turn both WFLG and VAL OFF and performs the requested service.
Note that when WFLG is ON, the client program ''must not'' turn VAL to on.
Field Summary Type DCT Default Read Write CA PP VAL Status USHORT Yes Yes Yes Yes WFLG Wait Flag USHORT No Yes Yes Yes
The label field (LABL) contains a string given to it that should describe the record in further detail. In addition to the DESC field. See "Fields Common to All Record Types" for more on the record name (NAME) and description (DESC) fields.
Field Summary Type DCT Default Read Write CA PP LABL Button Label STRING  Yes Yes Yes Yes NAME Record Name STRING  No Yes No No DESC Descriptor STRING  Yes Yes Yes No
The Permissive record has the alarm parameters common to all record types. "Alarm Fields" lists other fields related to a alarms that are common to all record types.
These fields are used to trigger monitors for each field. Monitors for the VAL field are triggered when OVAL, the old value field, does not equal VAL. Likewise, OFLG causes monitors to be invoked for WFLG when WFLG does not equal OLFG.
Field Summary Type DCT Default Read Write CA PP OVAL Old Status USHORT No Yes No No OFLG Old Flag USHORT No Yes No No
long (*process)(struct dbCommon *precord)
process() sets UDF to FALSE, triggers monitors on VAL and WFLG when they change, and scans the forward link if necessary.