Momentum-Apps/protocols/keeloq.c

/* Microchip HCS200/HCS300/HSC301 KeeLoq, rolling code remotes.
 *
 * Usually 443.92 Mhz OOK, ~200us or ~400us pulse len, depending
 * on the configuration.
 *
 * Preamble: 12 pairs of alternating pulse/gap.
 * Sync: long gap of around 10 times the duration of the short-pulse.
 * Data: pulse width encoded data. Each bit takes three cycles:
 *
 * 0 = 110
 * 1 = 100
 *
 * There are a total of 66 bits transmitted.
 *  0..31: 32 bits of encrypted rolling code.
 * 32..59: Remote ID, 28 bits
 * 60..63: Buttons pressed
 * 64..64: Low battery if set
 * 65..65: Always set to 1
 *
 * Bits in bytes are inverted: least significant bit is first.
 * For some reason there is no checksum whatsoever, so we only decode
 * if we find everything well formed.
 */

#include "../app.h"

static bool decode(uint8_t *bits, uint32_t numbytes, uint32_t numbits, ProtoViewMsgInfo *info) {

    /* In the sync pattern, we require the 12 high/low pulses and at least
     * half the gap we expect (5 pulses times, one is the final zero in the
     * 24 symbols high/low sequence, then other 4). */
    const char *sync_pattern = "101010101010101010101010" "0000";
    uint8_t sync_len = 24+4;
    if (numbits-sync_len+sync_len < 3*66) return false;
    uint32_t off = bitmap_seek_bits(bits,numbytes,0,numbits,sync_pattern);
    if (off == BITMAP_SEEK_NOT_FOUND) return false;

    info->start_off = off;
    off += sync_len; // Seek start of message.

    /* Now there is half the gap left, but we allow from 3 to 7, instead of 5
     * symbols of gap, to avoid missing the signal for a matter of wrong
     * timing. */
    uint8_t gap_len = 0;
    while(gap_len <= 7 && bitmap_get(bits,numbytes,off+gap_len) == 0)
        gap_len++;
    if (gap_len < 3 || gap_len > 7) return false;

    off += gap_len;
    FURI_LOG_E(TAG, "Keeloq preamble+sync found");

    uint8_t raw[9] = {0};
    uint32_t decoded =
        convert_from_line_code(raw,sizeof(raw),bits,numbytes,off,
            "110","100"); /* Pulse width modulation. */
    FURI_LOG_E(TAG, "Keeloq decoded bits: %lu", decoded);
    if (decoded < 66) return false; /* Require the full 66 bits. */

    info->pulses_count = (off+66*3) - info->start_off;

    bitmap_reverse_bytes(raw,sizeof(raw)); /* Keeloq is LSB first. */

    int buttons = raw[7]>>4;
    int remote_id = ((raw[7]&0x0f) << 24) |
                     (raw[6] << 16) |
                     (raw[5] << 8) |
                     (raw[4] << 0);
    int lowbat = (raw[8]&0x80) != 0;

    fieldset_add_bytes(info->fieldset,"raw",raw,9*2);
    fieldset_add_bytes(info->fieldset,"encr",raw,4*2);
    fieldset_add_hex(info->fieldset,"id",remote_id,28);
    fieldset_add_bin(info->fieldset,"s2 s1 s0 s3",buttons,4);
    fieldset_add_bin(info->fieldset,"low battery",lowbat,1);
    return true;
}

ProtoViewDecoder KeeloqDecoder = {
    .name = "Keeloq",
    .decode = decode,
    .get_fields = NULL,
    .build_message = NULL
};