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DCS-BIOS Integration

Most cockpit controls talk to DCS through DCS-BIOS. This page covers how that path is wired in firmware: the compact command IDs that cross the CAN bus, the generated headers, and the output addresses that drive LEDs and gauges. PanelBridge is the only tier that runs the DCS-BIOS library — see Firmware Tiers.

The controlId range

A control routes by its controlId. DCS-BIOS controls live in 0x8000–0x86FF; PanelBridge looks the ID up in its input map and calls sendDcsBiosMessage(). (Values below 0x8000 are HID — handled by SimGateway. See HID Controls.)

DCSIN_* — compact command IDs

A CAN frame carries only 8 data bytes — far too little for a DCS-BIOS ASCII command like "ARM_MASTER 1\n". So inputs send a compact DCSIN_* constant instead, generated sequentially from 0x8001. PanelBridge maps it back to the real command string.

// PanelGroup sketch — fire a compact ID, not a string:
OpenSkyhawk::Switch2Pos masterArm(DCSIN_ARM_MASTER, PinRef(PB5));

DCSIN_* constants are transport aliases, not device IDs. Multiple controls may share one DCSIN_* if they trigger the same DCS command — PanelBridge doesn't track which node sent it.

Output addresses — A_4E_C_*

Outputs (LEDs, gauges) go the other way: DCS-BIOS streams a state word, PanelBridge broadcasts it, and output objects pick out their value by address + bitmask from the generated headers:

  • A_4E_C_<NAME> — the 16-bit DCS-BIOS output address
  • A_4E_C_<NAME>_AM — the bitmask for the relevant bits
OpenSkyhawk::LED masterCaution(A_4E_C_MASTER_CAUTION, A_4E_C_MASTER_CAUTION_AM, PinRef(PB0));

No _A suffix

DCS-BIOS's own Addresses.h uses an _A suffix for these. The generated A4EC headers deliberately drop it and add the _AM mask companion. Always use A_4E_C_* / A_4E_C_*_AM — never the old _A form.

Input DCSIN_* IDs and output A_4E_C_* addresses are separate namespaces — an output address is never used as an input controlId.

Generated A4EC headers

The A4EC generator parses the A-4E-C DCS-BIOS JSON and emits committed headers under Firmware/Libraries/A4EC/ (currently 150 DCSIN_* constants):

Header Included by Contents
A4EC_CmdIds.h PanelGroup sketches DCSIN_* command-ID #defines
A4EC_InputMap.h PanelBridge only Sorted DcsBiosInputEntry[] lookup table
A4EC_OutputIds.h Output objects A_4E_C_* addresses + _AM masks

PanelBridge looks up each incoming DCSIN_* in A4EC_InputMap.h by binary search, then calls sendDcsBiosMessage() with the matched command name and the right argument for the control type (switch → "0"/"1", encoder → "DEC"/"INC", multipos → the integer, etc.).

The generator is maintainer tooling

The generated headers are committed — contributors do not run the generator. Refreshing them when a new A-4E-C release ships is a maintainer task (tools/gen_a4ec/). There is no DCS-BIOS version pinning today; refresh is manual.