Tongs

The Tongs

The tongs reach into the fire and pull out the glowing workpiece. Tongs are the fieldbus bridges of the ForgeIEC platform — they reach into the industrial periphery and bring process data safely to the PLC core.

Supported Protocols

Architecture: One Process per Segment

Each bridge runs as an independent process. anvild starts, monitors, and restarts bridges automatically. A bridge crash affects neither the PLC core nor other bridges.

anvild
  |-- tongs-modbustcp --config config.toml --segment mb1
  |-- tongs-modbustcp --config config.toml --segment mb2
  |-- tongs-ethercat  --config config.toml --segment ec1
  +-- tongs-profibus  --config config.toml --segment pb1

Communication between anvild and the bridges uses Anvil Technology (Zero-Copy Shared Memory). Each segment receives its own IPC channel.

Segment Hierarchy

Tongs organizes industrial communication in a hierarchy familiar from established PLC tools:

Bus Systems
+-- Modbus TCP: Hall 1 (eth0) [active]
|   +-- 192.168.1.100 -- Temperature Module (Slave 1)
|   |   +-- Temperature : INT (%IW0)   [Subscribe]
|   |   +-- Setpoint : INT (%QW10)     [Publish]
|   +-- 192.168.1.101 -- Pump (Slave 2)
+-- Modbus RTU: Lab (/dev/ttyUSB0)
+-- Unassigned (Scanner Pool)
    +-- 192.168.2.55 -- Unknown

Device Discovery

The integrated network scanner discovers field devices automatically:

• ICMP ping scan — determine reachable hosts in the subnet
• Port scan — check Modbus port (502) and other services
• Register scan — read Modbus registers and identify device type
• FDD device catalog — match known devices by their register signatures

Discovered devices land in the scanner pool and can be assigned to a segment via drag-and-drop.

Automatic Address Assignment

IEC addresses (%IX, %QW, %MD, etc.) are assigned globally and without collisions. Existing addresses in global variable lists are taken into account. The corresponding VAR_ANVIL transport blocks are generated automatically.

Direction Model

Each variable has a clear direction:

• in (Subscribe/Read) — bridge reads from field device, PLC receives
• out (Publish/Write) — PLC sends, bridge writes to field device

There is no “inout”. The bridge filters: only “in” variables are read (Modbus FC3), only “out” variables are written (Modbus FC5/FC6/FC16).

Configuration

Segments and devices are configured in config.toml:

[[bus_segments]]
id = "mb1"
protocol = "modbus_tcp"
enabled = true

[bus_segments.settings]
interface = "eth0"
port = 502

[[bus_segments.devices]]
name = "Temperature Module"
host = "192.168.1.100"
slave_id = 1

Technical Details