7/The Tango Pipe specification¶
This specification describes the Tango Pipe feature of a Device.
Copyright (c) 2019 Tango Controls
This Specification is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version. This Specification is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, see http://www.gnu.org/licenses.
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.
Tango Pipe is an Attribute [RFC-4] with custom data structure - the pipe name and pipe description. But in contrary of Commands or Attributes, a pipe does not have a pre-defined data type: it may be of any basic Tango data type (or array of) and this may change every time a pipe is read or written.
To pass big pieces of data structure at a time
To define complex data structures to act as a single Attribute
Device MAY define zero, one or more Pipes.
Pipe MUST have static metadata:
name = TangoName description = DevString [link to RFC-9 Data Types] label = DevString [link to RFC-9 Data Types] level = "OPERATOR"/"USER" writeType = "PIPE_READ"/"PIPE_WRITE" writable = DevBoolean
Pipe name MUST follow Tango naming conventions.
Pipe with writeType=”PIPE_READ” MUST be read only.
Pipe data structure MUST be:
Key(s) -> Value(s)
Key = DevString [link to RFC-9 Data Types] Value = Scalar or Array of Any Tango compliant type or Pipe [link to RFC-9 Data Types]
In Tango 9 “DevPipeBlob” is used to describe Value (see image below).
V10 NOTE: Attribute being a corner case of a Pipe can be considered as a derivative of a Pipe.
Pipe MUST NOT be polled.
Pipe MAY emit an event via Server API call.
Server API MUST provide a set of methods for a Server Client code to define a Pipe.
Server API MUST provide a way to fill the Pipe with data.
Client API MAY provide a way to obtain Pipe schema.
Client API MUST provide methods for a client to fetch Pipe data from a Device.
Client API MUST provide methods to traverse Pipe structure.