Real-Time IEC 61850 Fast Message Services Implementation in VxWorks

Table of Contents

Real-Time IEC 61850 Fast Message Services Implementation in VxWorks

This paper presents the design and realization of IEC 61850 Fast Message Transmission Services (FMTS) — specifically Sampled Value Messages (SV/SMM) and GOOSE messages — on the VxWorks real-time operating system. A Fast Communication Interface (FCI) is implemented to bypass the standard TCP/IP stack, enabling deterministic, low-latency communication directly over Ethernet.

⚡ Introduction
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IEC 61850 defines high-performance communication for substation automation systems. SMM/SV and GOOSE messages demand sub-millisecond latency, which the standard VxWorks TCP/IP stack cannot satisfy. The FMTS implementation requires:

Direct mapping from application/presentation layers to Ethernet data link.
Efficient real-time task scheduling.
Minimal processing overhead to meet <3 ms transmission requirements.

This work focuses on designing a Fast Communication Interface (FCI), implementing subscriber/publisher tasks, and optimizing real-time performance.

🛠 Analysis of Fast Message Transmission Services (FMTS)
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1.1 Abstract Communication Service Interface (ACSI)
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ACSI provides protocol-independent service definitions. FMTS messages use a publisher/subscriber model:

SMM (SV): Periodic, fixed datasets, high-frequency sampled values.
GOOSE (SGM): Event-driven with richer control parameters, fast retransmission upon events.

1.2 Specific Communication Service Mapping (SCSM)
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FMTS maps messages directly to Ethernet frames:

Uses dedicated multicast addresses and VLAN priority tagging.
APDUs/ASDUs encoded via ASN.1 BER.
Supports IEC 61850-9-1 simplified or 9-2 full sampled values.
GOOSE messages include control block references (GoCBRef), sequence numbers (StNum, SqNum), and Time Allowed to Live (TAL).

🖥 VxWorks Implementation
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2.1 Network Stack and MUX Layer
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VxWorks uses MUX/END driver model.
Standard applications access TCP/IP via sockets.
FMTS bypasses TCP/IP using a high-priority MUX protocol for deterministic delivery.

2.2 Fast Communication Interface (FCI)
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FCI provides direct Ethernet access for SMM/GOOSE:

fciOpen() / muxBind() — Registers interface in MUX with MUX_PROTO_SNARF.
fciMCastAddrSet() — Configures multicast addresses.
fciSend() — Builds and sends Ethernet frames (EtherType 0x88B8/0x88BA).
fciRcvRtn() — Receive callback for APDU validation and shared memory updates.
High task priorities and minimal FCI processing ensure low-latency delivery.

2.3 Application Tasks
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SRT (tSavReceiveTask) — SV subscriber decoding APDUs, updating shared memory.
GRT (tGooseReceiveTask) — GOOSE subscriber managing sequence numbers, TAL timeouts, and retransmissions.
GST / GSF (tGooseSendTask + fGooseSend) — GOOSE publisher with periodic and fast retransmission strategies.

Example pseudocode (GOOSE receive):

void GRT_Task() {
    while(1) {
        wait_for_signal();  
        decode_GoCBRef_TAL_StNum_SqNum(...);
        if (isValidNewEvent()) {
            decode_AllData();
            write_to_shared_memory();
            release_semaphore_to_protection_app();
        } else if (isRetransmission_or_Test()) {
            update_SqNum_and_timing();
        } else {
            handle_counter_error();
        }
    }
}