Anvil

The Anvil

In every forge, the anvil is the central piece — this is where metal is shaped, hardened, and refined. Anvil is the runtime environment of the ForgeIEC platform: the place where source code meets real-time execution.

Anvil manages the PLC scan cycle, the process images, and the data exchange between the PLC program and the fieldbus bridges. The runtime daemon anvild is the heartbeat of every ForgeIEC installation.

Architecture

+--------------+         +------------+         +------------------+
|              |         |            |         |                  |
| PLC Program  |<------->|  anvild    |<------->|  Modbus Bridge   |--> Field devices
|  (IEC Code)  |  gRPC   |  (Daemon)  |  Anvil  |  EtherCAT Bridge |--> Drives
|              |         |            |  SHM    |  Profibus Bridge  |--> Sensors
+--------------+         +------------+         |  OPC UA Bridge   |--> SCADA
                                                +------------------+

                         <-- Anvil -->
                         Zero-Copy IPC
                         Shared Memory

Real-Time Scan Cycle

The PLC core operates in a deterministic scan cycle:

1. Read inputs — acquire process image from the fieldbus bridges
2. Execute program — process the IEC code
3. Write outputs — distribute results to the bridges

The cycle runs with a configurable cycle time. Anvil guarantees deterministic behavior without dynamic memory allocation in the hot path.

Anvil Technology – Zero-Copy IPC

The data exchange between anvild and the protocol bridges uses Anvil Technology — a high-performance IPC channel based on zero-copy shared memory:

• Sub-microsecond latency — no serialization, no copies
• Lock-free algorithms — no blocking, no deadlocks
• Publish/Subscribe model — loose coupling between producer and consumer
• One channel per segment — isolation between bus systems

PUBLISH/SUBSCRIBE in the IEC Program

Anvil Technology integrates seamlessly into IEC 61131-3 programming:

VAR_GLOBAL PUBLISH 'Motors'
    K1_Mains    AT %QX0.0 : BOOL;
    K1_Speed    AT %QW10  : INT;
END_VAR

VAR_GLOBAL SUBSCRIBE 'Sensors'
    Temperature AT %IW0   : INT;
    Pressure    AT %IW2   : INT;
END_VAR

The PUBLISH/SUBSCRIBE keywords are a ForgeIEC extension of the IEC 61131-3 standard. The compiler automatically generates the Anvil bindings. In the editor, the corresponding VAR_ANVIL blocks are automatically generated and synchronized.

Bridge Management

anvild starts, monitors, and manages all fieldbus bridges as subprocesses:

• One process per segment — isolation and independent operation
• Automatic restart — crashed bridges are detected and restarted
• Configuration via TOML — config.toml defines segments, devices, and connection parameters
• gRPC interface — Forge Studio controls the daemon remotely

Compilation

The compilation follows a two-stage model:

1. Workstation: Forge Studio runs iec2c (IEC 61131-3 to C)
2. Target system: anvild generates a platform-specific Makefile and calls make (g++)

The IEC compiler (iec2c) only runs on the workstation. The target system requires make, g++, libstdc++ and librt to compile the generated C code at deployment time.

Technical Details