Finalize C <=> C++ interface

src/avclan/hal/board.h

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+// Copyright (C) 2026 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Clock setup + GPIO/pin configuration. Call once, first thing at startup
+// (before any peripheral init).
+void board_init(void);
+
+// Globally enable interrupts. Call after all peripherals are initialized.
+void board_enable_interrupts(void);
+
+#ifdef __cplusplus
+}
+#endif

src/avclan/hal/cd_timer.h

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+// Copyright (C) 2026 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// CDChanger periodic-timer HAL: the ~1 Hz tick that drives the CD changer's
+// status updates. The timer hardware is target-specific; the CD changer owns
+// what a tick means (see cdchanger.cc). The device polls cdtimer_pending() and
+// clears the tick with cdtimer_clear().
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// One-time hardware bring-up. Leaves the tick disabled.
+void cdtimer_init(void *ptr, void(clbk)(void *), bool(isplay)(void *));
+
+// Reset the count so the next tick is ~1 s out, and enable the tick.
+void cdtimer_reset(void);
+
+// Restore / disable the ~1 Hz tick.
+void cdtimer_restore(void);
+void cdtimer_disable(void);
+
+extern volatile bool cdtimer_pending_flag;
+
+static inline bool cdtimer_pending() { return cdtimer_pending_flag; }
+static inline void cdtimer_clear() { cdtimer_pending_flag = false; }
+
+#ifdef __cplusplus
+}
+#endif

src/avclan/hal/media.h

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+// Copyright (C) 2026 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// Media-control HAL: emulate head-unit button presses to the audio source. This
+// is device functionality (see CDChanger), so this contract is consumed only by
+// the device implementation, not the app.
+
+#pragma once
+
+#include "avclan.h"
+
+#ifdef __cplusplus
+using MediaAction = avclan::MediaAction;
+extern "C" {
+#else
+typedef enum MediaAction MediaAction;
+#endif
+
+// One-time hardware bring-up for the media driver.
+void media_init(void);
+
+// Emulate a media function (button press) on the source device.
+void media_action(MediaAction fn);
+
+#ifndef NDEBUG
+bool media_mic_toggle(void);
+bool media_busy(void);
+#endif
+
+#ifdef __cplusplus
+}
+#endif

src/avclan/hal/phy.h

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+// copyright (C) 2006 Marcin Slonicki <marcin@softservice.com.pl>
+// copyright (C) 2007 Louis Frigon
+// Copyright (C) 2015 Allen Hill <allenofthehills@gmail.com>
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#pragma once
+
+#include <stdint.h>
+
+#include "avclan.h"
+
+#ifdef __cplusplus
+using Read = avclan::detail::Error::Read;
+using Bit = avclan::detail::Bit;
+extern "C" {
+#else
+typedef enum Read Read;
+typedef enum Bit Bit;
+#endif
+
+// One-time bring-up of the bus hardware. Leaves the bus idle and TX unmuted.
+void phy_init(void);
+
+// Mute/unmute device TX. "Muted" means we still listen, we just don't ACK or
+// transmit.
+void phy_mute(bool mute);
+bool phy_is_muted(void);
+
+// True when there is activity on the bus (something is driving it).
+bool phy_active(void);
+
+// Bus-transaction guard: quiesce the target's other async sources around a bus
+// read/send so framing isn't disturbed, then restore them. May be a no-op on a
+// target without such contention.
+void phy_guard_enter(void);
+void phy_guard_leave(void);
+
+// Start-bit handling, factored out of read/sendframe so the framing layer holds
+// no bus-timing or hardware-recovery logic.
+// - phy_read_startbit waits for and validates an incoming start bit, doing
+//   any target-specific bus recovery; see avclan::detail::Error::Read.
+// - phy_send_startbit acquires the bus and emits a start bit; returns false
+//   if the bus was busy.
+Read phy_read_startbit(void);
+bool phy_send_startbit(void);
+
+// Per-symbol I/O. The send* helpers return the even parity of the bits sent;
+// the read* helpers return the even parity of the bits read. The _u8/_u16
+// suffixes name the source-operand width; `len` is how many bits (<= width).
+void phy_send_bit(Bit bit);
+void phy_send_ack(void);
+uint8_t phy_read_ack(void);
+
+Bit phy_send_bits_u8(const uint8_t *bits, int8_t len);
+Bit phy_send_bits_u16(const uint16_t *bits, int8_t len);
+Bit phy_send_byte(const uint8_t *byte);
+
+uint8_t phy_read_bits_u8(uint8_t *bits, uint8_t len);
+uint8_t phy_read_bits_u16(uint16_t *bits, int8_t len);
+uint8_t phy_read_byte(uint8_t *byte);
+
+#ifndef NDEBUG
+// Sample and dump bus bit timing over the serial link (REPL `M`).
+void phy_measure(void);
+#endif
+
+#ifdef __cplusplus
+}
+#endif