Functions

The TCU exposes gRPC services enabling external systems to:

• Enable and disable heaters
• Configure thermal control modes
• Update temperature setpoints
• Configure control loop parameters

Command acknowledgements shall be returned through the same gRPC communication channel.

The TCU provides thermal telemetry through gRPC services, including:

• Temperature measurements
• Heater states
• Control loop status
• Fault and warning information

Telemetry shall be available via:

• On-demand requests
• Continuous server-side or bi-directional streaming services

Fault Reporting

The TCU shall expose fault and event reporting services allowing:

• Retrieval of current fault status
• Notification of newly detected faults
• Support for diagnostic and maintenance activities

Interface Definition Language

All gRPC services, messages, and data structures shall be defined using Protocol Buffer (.proto) files.

The .proto definitions shall:

• Serve as the authoritative interface specification
• Be subject to configuration management
• Be used for automatic generation of client and server code

Version Control

Interface versions shall be managed to ensure:

• Backward compatibility where applicable
• Controlled evolution of services
• Traceability between interface versions and subsystem releases

Performance Considerations

The gRPC interface is intended for:

• Supervisory control
• Configuration management
• Telemetry and health monitoring

Time-critical and hard real-time thermal control functions shall be executed internally within the TCU and shall not rely on the gRPC interface.

The gRPC interface supports:

• Transport Layer Security (TLS)
• Client and server authentication mechanisms
• Access control to prevent unauthorised commanding

Security mechanisms shall be configurable in accordance with mission-level security requirements.

Assembly, Integration, and Test

The gRPC over Ethernet interface facilitates:

• Subsystem-level functional testing
• Thermal verification and validation
• Use of standard IP-based test equipment and software tools

This interface reduces the need for dedicated test interfaces during AIT.

Application Package

The delivered application package includes the networking services and middleware required for communication between the TCU and the host platform. The following services are supported:

• HTTP service interface over TCP
• HTTP/2 transport layer
• gRPC communication framework with Proto3 payload handling
• NTP time synchronization (UDP port 123)
• TFTP file transfer service (UDP port 69)

Ethernet and Hardware Interface

• PHY interface: RMII
• Ethernet link rates: 10 / 100 Mbps
• Typical TCP throughput on a 100 Mbps link: approximately 60–95 Mbps depending on traffic profile and packet size

Networking Stack and Capacity:

The networking architecture is implemented using an RTOS-based environment:

• Operating system: FreeRTOS
• TCP/IP stack: lwIP

Supported network profile:

• IPv4 communication
• DHCP client support

Current network capacity configuration:

• Concurrent TCP sessions: up to 8 active TCP PCBs
• Listening server sockets: up to 4 TCP listening PCBs
• UDP sockets: 4 UDP PCBs

These parameters can be tuned depending on the final application requirements and memory allocation.

HTTP/2 and gRPC Profile:

The current implementation supports the following operational characteristics:

• HTTP/2 concurrent streams: up to 8 streams per connection
• HTTP/2 header block size: 512 bytes
• Per-stream request payload budget: 512 bytes
• Per-stream pending response buffer: 320 bytes

The gRPC implementation supports:

• Unary RPC calls
• Streaming RPC
• Bidirectional streaming