/**
 * @file fhss.h
 * @brief FHSS channel sequencer based on AES-128-ECB.
 *
 * Both link endpoints derive the same hopping sequence independently from a
 * shared 128-bit key and a monotonically increasing slot counter.  No
 * synchronisation traffic is required as long as both sides start from the
 * same slot.
 */
#pragma once
#include <stdint.h>

/** Dwell time per channel in milliseconds. */
#define FHSS_DWELL_MS 2u

/** Number of channels in the hopping sequence. */
#define FHSS_CHANNELS 40u

/** @brief Reset the slot counter to zero. */
void fhss_init(void);

/**
 * @brief Return the next channel in the hopping sequence and advance the slot.
 * @return Channel index in [0, 39].
 */
uint8_t fhss_next_channel(void);

/** @brief Advance the slot counter by one (receiver side, no packet received). */
void fhss_sync_tick(void);

/**
 * @brief Force the slot counter to a specific value for RX synchronisation.
 * @param s New slot value.
 */
void fhss_set_slot(uint32_t s);

/** @brief Return the current slot counter value. */
uint32_t fhss_get_slot(void);