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/**
* HDLC frame helpers — flags, bit-stuff, FCS-CCITT (AX.25).
* SPDX-License-Identifier: GPL-3.0-or-later
*/
#ifndef S1224_HDLC_H
#define S1224_HDLC_H
#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>
#define HDLC_FLAG 0x7Eu
#define HDLC_FCS_INIT 0xFFFFu
#define HDLC_FCS_GOOD 0xF0B8u
#define HDLC_MAX_INFO 512
uint16_t hdlc_fcs_update(uint16_t fcs, uint8_t byte);
uint16_t hdlc_fcs_final(uint16_t fcs);
/**
* Build on-wire bit stream (NRZI already applied by caller after this):
* FLAG + stuffed(info + FCS_lo + FCS_hi) + FLAG(+optional trailing flags).
* Returns bit count written to bits[] (MSB-first within each stuffed byte stream
* is not used — output is a raw bit array, LSB-first per AX.25 bit order).
*
* bits_cap is capacity in bits. Returns 0 on overflow / bad args.
*/
size_t hdlc_encode_bits(const uint8_t *info, size_t info_len,
uint8_t *bits, size_t bits_cap,
unsigned trailing_flags);
/**
* Feed one NRZ bit (after NRZI decode). Returns true when a complete good
* frame is available in out[] (info only, FCS stripped).
*/
typedef struct {
uint8_t buf[HDLC_MAX_INFO + 2];
size_t len;
uint8_t ones;
bool in_frame;
bool stuffing;
uint8_t byte_acc;
uint8_t bit_count;
} hdlc_rx_t;
void hdlc_rx_init(hdlc_rx_t *rx);
bool hdlc_rx_bit(hdlc_rx_t *rx, bool bit, uint8_t *out, size_t *out_len);
#endif /* S1224_HDLC_H */
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