Loopback

The loopback node-type loops back every sample which has been sent to it. Internally it is implemented by a FIFO queue.

It can be used to chain multiple paths together by using the same loopback node as an output node in the first path and as a source in the second path.

Prerequisites

This node-type does not have any special library dependencies. It is always available.

Implementation

The source code of the node-type is available here: https://github.com/VILLASframework/node/blob/master/lib/nodes/loopback.cpp

Configuration

queuelen	integer >= 0 The queue length of the internal queue which buffers the samples.
samplelen	integer >= 0 The number of values each buffered sample can store.
mode	string Default: "auto" Enum: "pthread" "polling" "pipe" "eventfd" "auto" Specify the synchronization mode of the internal queue.
	object (Input configuration (received by VILLASnode))
vectorize	integer Default: 1 This setting allows to send multiple samples in a single message to the destination nodes. The value of this setting determines how many samples will be combined into one packet.
	Array of Hook Object (object) or Hook Name (string) (hook_list)
builtin	boolean (Builtin hook functions) Default: true By default, each node and paths has a couple of default hooks attached to them. With this setting the attachment of built-in hooks can be disabled.
	object (Output configuration (sent out by VILLASnode))

{

• "queuelen": 0,
• "samplelen": 0,
• "mode": "pthread",
• "in": {

  • "signals": [

    • {

      • "name": "tap_position",
      • "type": "integer",
      • "init": 0

      },
    • {

      • "name": "voltage",
      • "type": "float",
      • "unit": "V",
      • "init": 230

      }

    ],
  • "vectorize": 1,
  • "hooks": [

    • "print",
    • {

      • "type": "limit_rate",
      • "rate": 1000

      }

    ]

  },
• "vectorize": 1,
• "hooks": [

  • "print",
  • {

    • "type": "limit_rate",
    • "rate": 1000

    }

  ],
• "builtin": true,
• "out": {

  • "vectorize": 0,
  • "hooks": [

    • "print",
    • {

      • "type": "limit_rate",
      • "rate": 1000

      }

    ]

  }

}

Example

node/etc/examples/nodes/loopback.conf

nodes = {
    loopback_node = {
        # A loopback node will receive exactly the same data which has been sent to it
        type = "loopback"

        # The internal implementation is based on queue
        # The queue length of the internal queue which buffers the samples
        queuelen = 1024

        # Use busy polling for synchronization of the read and write side of the queue
        mode = "polling"
    }
}