Bus segments | ForgeIEC

Affects: ForgeIEC Studio tongs-* Anvil server (anvild)

What is a segment?

A bus segment is one physical network on one interface of the PLC target — Ethernet port (eth0, enp3s0) for Modbus TCP / EtherCAT / EtherNet-IP, serial port (/dev/ttyUSB0) for Modbus RTU / Profibus DP.

For each segment, anvild starts exactly one bridge daemon (tongs-modbustcp, tongs-ethercat, …). It handles traffic to all devices in the segment.

A project can hold any number of segments — each with its own protocol, interface and polling rate. A fast EtherCAT axis control (eth1, 1 ms) + a slow Modbus TCP sensor acquisition (eth0, 100 ms) run in parallel in the same project.

Segment fields

The struct definition lives in editor/include/model/FBusSegmentConfig.h. A segment is persisted in the .forge project as <fi:segment> under <fi:busConfig> (see bus configuration).

Identity + protocol

Field	Type	Meaning
`segmentId`	UUID	Stable primary key — generated on creation, not editable. Survives rename, protocol switch, IP change.
`protocol`	Enum	`modbustcp` / `modbusrtu` / `ethercat` / `profibus` / `ethernetip`. Determines which bridge daemon starts.
`name`	String	User label (e.g. `"Halle1"`). Free choice, visible in tree + logs, is part of the IEC namespace (`anvil.Halle1.<Device>.<Var>`).
`enabled`	Bool	On/off switch. `false` = bridge is not started, devices stay offline. Default: `true`.

Interface + routing

Field	Type	Meaning
`interface`	String	Network interface (`eth0`, `/dev/ttyUSB0`). Bridge passes it to the socket / serial API.
`bindAddress`	String (IP/CIDR)	Source IP for outbound TCP connections, e.g. `192.168.24.100/24`. Empty = OS picks automatically.
`gateway`	String (IP)	Default gateway for packets leaving the local subnet. Empty = no gateway.
`pollIntervalMs`	Int (ms)	Polling interval of the bridge. `0` = as fast as possible. Typical: `100` for Modbus TCP, `0` for EtherCAT.

Network settings (advanced)

For cases where OS defaults are not enough — typically: many parallel TCP connections per slave, long-running sessions across NAT, multiple subnets on one NIC.

Field	Type	Meaning
`subnetCidr`	String (CIDR)	Local subnet of the segment. Allows per-device gateway overrides when the NIC carries multiple networks.
`sourcePortRange`	String `"min-max"`	TCP source-port pool, e.g. `30000-39999`. Empty = ephemeral OS range. Important when many parallel connections go to the same slave.
`keepAliveIdleSec`	Int (s)	Idle seconds before the first TCP keep-alive. `0` = OS default.
`keepAliveIntervalSec`	Int (s)	Distance between probes. `0` = OS default.
`keepAliveCount`	Int	Number of failed probes before a connection is declared dead. `0` = OS default.
`maxConnections`	Int	Connection-pool cap. `0` = unlimited. Protection against slaves with a hard connection limit.
`vlanId`	Int (1..4094)	802.1Q VLAN tag. `0` = untagged.

Protocol-specific settings

The settings map (key/value) carries values that only make sense for a specific protocol:

Protocol	Typical settings
`modbustcp`	`port`, `timeout_ms`
`modbusrtu`	`serial_port`, `baud_rate`, `parity`, `stop_bits`
`ethercat`	`dc_sync_shift_ns`, `cycle_time_us`
`profibus`	`master_address`, `baud_rate`

Plus protocol-independent: log_level, log_file.

Edit path in ForgeIEC Studio

Both paths in the bus tree panel are equivalent:

Action	Effect
Single click on a segment node	`FPropertiesPanel` (right) shows all fields as inline editors. Changes are written into the project on `editingFinished` + the dirty flag is set.
Double click	Modal dialog `FSegmentDialog` with the same field set, grouped into General / Protocol / Advanced Network / Logging. OK applies, Cancel discards.

Bridge lifecycle

When you create a segment with enabled=true and save:

anvild notices the new segment on the next project push
anvild’s subprocess manager spawns the matching bridge daemon (tongs-<protocol>) with the segment ID as an argument
Bridge opens the configured interface + connects to each device
Live status flows via Anvil zero-copy IPC between bridge and PLC runtime — no TCP loopback latency
If the bridge crashes, anvild restarts the daemon automatically; the PLC logic continues uninterrupted

Bridge status per segment is reachable via MCP bellows.protocol_status, or directly as a colour indicator in the bus panel (green/yellow/red/grey).

Example: Modbus TCP segment

[[bus_segments]]
segment_id     = "a3f7c2e1-7c4f-4e1a-9f9c-1a2b3c4d5e6f"
protocol       = "modbustcp"
name           = "Halle1"
enabled        = true
interface      = "eth0"
bind_address   = "192.168.24.100/24"
gateway        = ""
poll_interval  = 100

[bus_segments.settings]
port           = "502"
timeout_ms     = "2000"
log_level      = "info"
log_file       = "/var/log/forgeiec/halle1.log"

Effect:

tongs-modbustcp starts on eth0 with source IP 192.168.24.100
Polls all devices at 100 ms
Allows up to 2000 ms per request before timeout
Logs to /var/log/forgeiec/halle1.log
IEC variables reachable as anvil.Halle1.<Device>.<...>