OpenSFF Management Module Specification

7. KVM Signal Routing

The Management Module (MM) is responsible for selecting and controlling console access (keyboard, video, and mouse) across all installed compute nodes in an enclosure.

Enclosures provide passive routing infrastructure: one USB 2.0 uplink and one DisplayPort output from each node are multiplexed to the MM slot. The enclosure does not interpret or emulate signals; it only forwards the active path selected by the MM.

7.1 Signal Multiplexing Interface

The MM interfaces with the enclosure’s multiplexer subsystem, which accepts one USB 2.0 and one DisplayPort signal from each node.

The MM MUST:

• Drive the multiplexer select lines to determine which node’s console is active.
• Ensure that only one node is selected at a time.
• Prevent invalid or conflicting signal states.
• Maintain full compatibility with USB 2.0 and DisplayPort 1.4 electrical standards.

The MM SHALL assume that the enclosure preserves full signal integrity and prevents interference from non-selected nodes.

7.2 Slot Selection Control

Slot selection is always under MM control. Enclosures SHALL NOT implement independent slot selection or override mechanisms.

The MM MUST provide a reliable method for users to select or change the active slot, through either:

• Hardware interface: Local buttons or switches driving the multiplexer directly.
• Software interface: Anchor Linux services exposing slot selection via the Rust backend and Flutter frontend.

Regardless of implementation, the MM drives the multiplexer select lines and owns slot selection logic.

7.3 Visual Slot Identification

The Management Module (MM) MUST provide a means of indicating the currently selected compute node for KVM redirection.

• Pass-through MMs:

  • MUST provide a physical visual indicator on the module itself.
  • Acceptable display methods include:
    • A numeric 7-segment display (e.g., Slot 1–9 or hexadecimal 0–F).
    • A segmented alphanumeric or OLED display.
    • A user-configurable LED matrix.
  • The physical indicator MUST directly reflect the slot index selected by the multiplexer control signals.

• Full-featured MMs:

  • MUST provide this indication in software, as part of the Anchor Linux IP-KVM user interface.
  • If a physical indicator is provided, it MUST also accurately reflect the multiplexer selection state.

Note: In configurations where the MM performs blind slot selection (i.e., without reading slot presence data), the indication, whether physical or software, reflects only the current selection state. It does not guarantee that a node is present or operational in the selected slot.

7.4 Implementation Notes

The Management Module specification recognizes two implementation classes:

• Pass-through MM
  • Relies on a hardware control element (e.g., momentary push-button switch, stepped rotary switch)
  • Directly forwards the active USB 2.0 and DisplayPort signals after multiplexing
  • No interpretation, buffering, or format conversion is performed
• Full-featured MM
  • Includes a CPU and software stack (Anchor Linux) for remote KVM functionality.
  • Video signals must be made available to the CPU as a standard USB video device (UVC).
  • Conversion of DisplayPort signals into a format consumable by UVC capture is REQUIRED, but the method is left to vendor implementation.
  • USB 2.0 signals are forwarded and managed through software.

General requirements:

• The specification does not mandate a specific conversion architecture for video capture. Vendors MAY use any standards-compliant method (e.g., bridging or protocol translation) that results in a valid UVC stream.
• Multiplexer control MUST remain deterministic and synchronized across both USB and DisplayPort paths.
• Enclosures and MMs MUST preserve full compliance with DisplayPort 1.4 and USB 2.0 electrical specifications, regardless of implementation details.