Device Communication

Overview

FieldLine Industries’ devices use a full-duplex asynchronous serial protocol for data streaming and control. The device TX -> host RX link supports multiple simultaneous data streams at a configurable samplerate as well as register values upon request. The Host TX -> device RX link is used for stream configuration and register access requests.

Device URI

The concept of a device URI is introduced to abstract the connection transport used to communicate with the device and support current and future methods of connection via a consistent interface. It is a : delimited string describing the transport and transport specific arguments required to connect to a device.

UART Transport

Devices may be connected directly to a host serial port using RS-232, RS-422, or USB converters which may be built-in or external to the device. These are all available through host drivers as a serial port and use the ‘uart’ transport:

URI Format: uart:<device>[:<baudrate>]

  • <device>: serial port device (mandatory), e.g. /dev/ttyACM0 on Linux or COM1 on Windows

  • <baudrate>: serial port baud rate (optional, defaults to 921600)

RFC2217 Transport

Devices connected to a host serial port as described above may be exposed to the network via a service which supports the RFC2217 protocol such as ser2net. The primary advantage of this approach over the raw TCP transport described below is dynamic control of the serial baudrate. The following ser2net.yaml can be used as an example:

connection: &serial0
  accepter: telnet(rfc2217),tcp(nodelay=true),7000
  connector: serialdev,/dev/ttyACM0,921600n81,local

This can be used as depicted below:

+-----------------+            +---------+
|     Host A      |   TCP/IP   | Host B  |   Serial   +-------+
|-----------------| <--------> |---------| <--------> | SMx00 |
| pyflind RFC2217 |            | ser2net |            +-------+
+-----------------+            +---------+

URI Format: rfc2217:<host>[:<port>[:<baudrate>]]

  • <host>: hostname or IP address of Host B (mandatory)

  • <port>: TCP port on which Host B is listening (optional, defaults to 7000, mandatory if baudrate supplied)

  • <baudrate>: serial port baud rate (optional, defaults to 921600)

TCP Transport

Devices may also be connected across a TCP/IP network by using a raw TCP-Serial redirector application on a host which is physically connected to the device serial port. The pyserial tcp_serial_redirect.py example or socat program can be used to expose the serial device to the network at a single pre-determined baudrate. For example, socat cat be run as follows assuming the serial device is already running at the specified baudrate:

$ socat TCP-LISTEN:7777,reuseaddr,fork,keepalive,nodelay FILE:/dev/ttyACM0,raw,echo=0,b921600

This can be used as depicted below:

+-------------+            +-----------------------+
|   Host A    |   TCP/IP   |        Host B         |   Serial   +-------+
|-------------| <--------> |-----------------------| <--------> | SMx00 |
| pyflind TCP |            | TCP-serial redirector |            +-------+
+-------------+            +-----------------------+

URI Format: tcp:<host>[:<port>]

  • <host>: hostname or IP address of Host B (mandatory)

  • <port>: TCP port on which Host B is listening (optional, defaults to 7777)