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+#ifndef THROTTLE_QUADRANT_PROTOCOL_HPP
+#define THROTTLE_QUADRANT_PROTOCOL_HPP
+
+#include "utilities.hpp"
+
+#include <Arduino.h>
+
+//! All our custom code lives in its own name space to avoid collisions.
+namespace tq::protocol {
+
+//! A message as received from the throttle quadrant.
+struct [[gnu::packed]] message {
+  //! The current throttle value (unit TBD).
+  byte throttle;
+  //! The current propeller speed value (unit TBD).
+  byte propeller_speed;
+  //! The current mixture value (unit TBD).
+  byte mixture;
+
+  //! The state (pressed/released) of the first trigger.
+  byte trigger_1 : 1;
+  //! The state (pressed/released) of the second trigger.
+  byte trigger_2 : 1;
+  //! The state (pressed/released) of the third trigger.
+  byte trigger_3 : 1;
+  //! The state (pressed/released) of the fourth trigger.
+  byte trigger_4 : 1;
+  //! The state (pressed/released) of the fifth trigger.
+  byte trigger_5 : 1;
+  //! The state (pressed/released) of the sixth trigger.
+  byte trigger_6 : 1;
+
+  //! Whether the throttle is idle or not.
+  byte throttle_idle : 1;
+
+  //! Whether the throttle is feathered or not (?).
+  byte propeller_feather : 1;
+
+  //! Whether the mixture is cut off or not.
+  byte mixture_cutoff : 1;
+
+  //! Reserved bits.
+  byte : 7;
+};
+
+//! Initialize the protocol handling subsystem.
+auto init() -> void;
+
+//! Start a run of the protocol handling subsystem.
+//!
+//! A new run is only started if there is not current run ongoing.
+//!
+//! @return true iff. a new run was started, false otherwise.
+auto start() -> bool;
+
+//! Perform the synchronous SPI transfer, if one is pending.
+//!
+//! Perform the final synchronous transfer from the throttle quadrant. If no
+//! new data is available, an empty optional is returned.
+//!
+//! @return An optional object containing a new message if one is available.
+auto perform_transfer() -> optional<message>;
+
+//! @internal
+//! Process the "data ready" signal coming from the throttle quadrant.
+//!
+//! When the throttle quadrant pulls the "data ready" line low, we know that
+//! there is new data available to be read out. We must adhere to a somewhat
+//! strict timing protocol, as detailed in the implemenation of this function.
+auto on_data_ready() -> void;
+
+//! @internal
+//! Process the "start delay" signal coming from the throttle quadrant.
+//!
+//! After notifying us about the data being ready, the "data ready" line will
+//! be deasserted. However, we must wait an additional 1.2ms before we start
+//! the transfer.
+auto on_start_delay() -> void;
+
+//! @internal
+//! Process the end of the start delay.
+//!
+//! The data is of the throttle quadrant is now ready to be read.
+auto on_start_delay_passed() -> void;
+
+}
+
+#endif
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