Overview

To show OpenVMS V9.2 X86_64 processing in an edge environment, a multi-threaded ‘C’ application was developed. The program uses serial connected RFID readers to identify and track model railroad cars (rolling stock) on a G-scale model railroad loop. The railroad loop is divided into five sections (blocks). The same program uses GPIO output signals to control track signals for those blocks and maintain train (consist) separation. RabbitMQ message broker is employed to distribute (publish) block and consist information and to accept commands for loop operation.

Rolling Stock Detection and Identification

RFID readers are used to detect movement and identify rolling stock on the model railroad loop. Each block has an RFID reader mounted beneath the track at the start of that block. The readers are each connected to the OpenVMS serial ports provided by SYS$YPDRIVER (devices TTA through TTE). A dedicated process thread is created, one for each reader device (train block). Each of these block threads assigns a channel to the reader port, initializes the reader and prepares the reader to read/detect an RFID tag. The RFID readers used initialize and communicate at 115,200 baud.

Each piece of model railroad rolling stock has an RFID tag mounted on its underside. As each piece of rolling stock enters a train block, the RFID tag passes over that block’s RFID reader and the tag’s value is read. An in memory database of tag values is queried and the rolling stock identified. The rolling stock database contains a description for each piece of rolling stock as well as other attributes (locomotive, car type, end of train car, etc.).

RFID reader mounted under track at block entrances.		RFID tags mounted on rolling stock undersides.

When an RFID tag is read for the first time, an inventory operation is begun. The first, and successive, tags are read and assembled into a running set of train cars (rolling stock) called a consist. Once completed, the consist is tracked as it travels from block to block and the RFID tags are scanned.

RFID tags being read as consist enters a train block and each rolling stock RFID tag passes over RFID reader.

Train Block Control

Two blocks on the train layout have block signals. One block also has an entry and approach signal. When a block’s block signal is set to STOP, a consist entering that block will pause. When a block’s block signal is set to PROCEED, a consist entering that block will continue through that block or resume forward movement is paused. A block’s signal state (STOP or PROCEED) is set based on whether or not the next block in the model railroad loop is occupied or vacant.

The signals on this layout are controlled using Direct Current (DC) pulses. Using an Alternating Current (AC) voltage source, an AC relay board and diodes, a block’s control voltage can be selected using GPIO output signals.

Publishing Block Status and Train (Consist) Position using RabbitMQ

Two publishing threads are created by the loop control application. Each thread uses a RabbitMQ Exchange to dynamically distribute loop information. The Exchange names are based on the name of name of the railroad loop being controlled, South Main1. The first exchange is named South Main1 Blocks and distributes running state and occupancy information for the loop. The second exchange is named South Main1 Consists and publishes consist position information. The name of a consist, taken from the lead locomotive description, is used as a RabbitMQ exchange routing key. This allows individual consist updates to be subscribed to.

Receiving Loop Commands using RabbitMQ

Also included in the application is a command processing thread. That thread subscribes to the RabbitMQ queue South Main1 Commands. Publishing a text string command to this queue wakes up the command processing thread which receives, parses and processes the sent command. The commands PROCEED, HOLD and STOP can be used to set individual loop blocks to a proceed, manual pause or momentary pause (one cycle pause), respectively. A SHUTDOWN command is also recognized to perform an orderly shutdown of the train loop.