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DCS-BIOS vs HID Controls

Every control you add to a panel takes one of two paths to DCS: the DCS-BIOS path or the HID path. Choosing correctly is the single most important decision when implementing a panel — it determines whether the control "just works" or whether every builder has to bind it by hand. Read this page before you wire up a new control.

The decision rule

Default to DCS-BIOS for everything. Use HID only for momentary controls that have no DCS-BIOS address, or for flight-control axes. HID controls require manual binding in DCS input settings or a provided profile — that's friction for every builder and kit buyer, so don't reach for it unless you have to.

The two paths

Everything travels the CAN bus in the same ControlPacket format. The controlId decides the path, and the routing happens at different tiers:

Path controlId range Routed by What DCS needs from the user
DCS-BIOS 0x8000–0x86FF PanelBridge Nothing beyond running DCS-BIOS export
HID < 0x8000 SimGateway Manual input binding or a provided .lua profile

DCS-BIOS path

For any control that has a DCS-BIOS address. The state is managed by DCS-BIOS itself, and the control syncs automatically — flip a switch in the pit and it moves in the sim, change it in the sim and your LED or gauge follows. Zero DCS setup beyond running the DCS-BIOS export.

A PanelGroup node fires a compact DCSIN_* command ID in the 0x8000–0x86FF range. PanelBridge looks it up in its generated input map and calls sendDcsBiosMessage() with the real DCS-BIOS command string. The node never knows the command name — only the compact ID.

This is why the entire A-4E-C control set works without any per-control declarations in a sketch: the generated input map already covers it.

HID path

For controls with no DCS-BIOS address — purely stateless momentary controls, and flight controls. These are handled entirely at the SimGateway layer as standard joystick axes and buttons; PanelBridge never sees them. A node fires a controlId below 0x8000, PanelBridge wraps it in a HID frame, and SimGateway applies it to the USB HID report.

Why HID adds friction

A DCS-BIOS control is bound by name inside the module — it works the moment DCS-BIOS is running. A HID control is just an anonymous joystick axis or button as far as Windows and DCS are concerned, which means:

  • Manual binding. Someone has to open DCS input settings and map each axis and button, or import a provided .lua profile.
  • Profile maintenance. That profile has to be kept in step with the firmware's button and axis assignments.
  • Platform limits. DirectInput exposes 8 axes, 128 buttons, and 4 POV hats per device — generous, but finite, and shared across the whole cockpit's HID surface.

Multiply that across a cockpit's worth of panels and the DCS-BIOS path is clearly the one you want by default.

When HID is the right choice

HID is correct in exactly two situations:

  1. Flight-control axes. The A-4E-C exposes no axis exports through DCS-BIOS — stick, throttle, and rudder are HID-only inputs. HID is mandatory here. This is the main reason the HID path exists, and it's primarily for the planned replica HOTAS.
  2. Momentary controls with no DCS-BIOS address. A purely stateless button (trigger, pickle) that the A-4E-C only accepts as a raw input, with no DCS-BIOS command behind it.

The seven planned HID axes are Roll, Pitch, Throttle, Rudder, Left Brake, Right Brake, and Zoom — 7 of the 8 DirectInput axis slots. The speed brake is not an axis — it's a DCS-BIOS on/off switch.

The controlId ranges

Range Type Path Handler
0x0010–0x001F HID axes HID SimGateway → HIDAxis
0x0020–0x002F HID hat switches HID SimGateway → HIDHatSwitch
0x0030–0x00AF HID buttons HID SimGateway → HIDButton
0x00B0–0x00FF Reserved HID expansion — not exposed by the current USB report
0x8000–0x86FF DCS-BIOS compact IDs (DCSIN_*) DCS-BIOS PanelBridge → sendDcsBiosMessage()
0xFFFF Reserved / invalid sentinel — dropped

Practical examples — the Armament Group

The Center Console Armament Group is almost entirely DCS-BIOS, because nearly every armament control has a DCS-BIOS address:

  • Armament panel switches (e.g. the master arm switch) — DCS-BIOS path. A two-position switch fires its DCSIN_* ID with value 0 or 1; PanelBridge sends the matching DCS-BIOS command. No binding needed.
  • AWRS panel rotary and selector controls, Misc Switch panel switches — DCS-BIOS path, same pattern, multi-position controls send a position index.
  • A bomb-release / pickle button would use the HID path only if the A-4E-C had no DCS-BIOS command for it; if a DCS-BIOS address exists, use it.

The flight stick that eventually mounts in front of this console is the opposite case — its axes and trigger go through HID, because that's the only path DCS offers for them.

Output addresses are a different namespace

Don't confuse input controlIds with output addresses. Output objects (LEDs, gauges) use A_4E_C_* address constants and A_4E_C_*_AM bitmasks from the generated headers — a separate namespace that is never used as an input controlId. (And note the generated headers omit the old _A suffix.)