Momentum-Apps/protocols/tpms/schrader_eg53ma4.c

/* Schrader variant EG53MA4 TPMS.
 * Usually 443.92 Mhz OOK, 100us pulse len.
 *
 * Preamble: alternating pulse/gap, 100us.
 * Sync (as pulses and gaps): "01100101", already part of the data stream
 * (first nibble) corresponding to 0x4
 *
 * A total of 10 bytes payload, Manchester encoded.
 *
 * 0 = 01
 * 1 = 10
 *
 * Used in certain Open cars and others.
 */

#include "../../app.h"

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

    const char *sync_pattern = "010101010101" "01100101";
    uint8_t sync_len = 12+8; /* We just use 12 preamble symbols + sync. */
    if (numbits-sync_len+8 < 8*10) return false;

    uint64_t off = bitmap_seek_bits(bits,numbytes,0,numbits,sync_pattern);
    if (off == BITMAP_SEEK_NOT_FOUND) return false;
    FURI_LOG_E(TAG, "Schrader EG53MA4 TPMS preamble+sync found");

    info->start_off = off;
    off += sync_len-8; /* Skip preamble, not sync that is part of the data. */

    uint8_t raw[10];
    uint32_t decoded =
        convert_from_line_code(raw,sizeof(raw),bits,numbytes,off,
            "01","10"); /* Manchester code. */
    FURI_LOG_E(TAG, "Schrader EG53MA4 TPMS decoded bits: %lu", decoded);

    if (decoded < 10*8) return false; /* Require the full 10 bytes. */

    /* CRC is just all bytes added mod 256. */
    uint8_t crc = 0;
    for (int j = 0; j < 9; j++) crc += raw[j];
    if (crc != raw[9]) return false; /* Require sane CRC. */

    info->pulses_count = (off+10*8*2) - info->start_off;

    /* To convert the raw pressure to kPa, RTL433 uses 2.5, but is likely
     * wrong. Searching on Google for users experimenting with the value
     * reported, the value appears to be 2.75. */
    float kpa = (float)raw[7]*2.75;
    int temp_f = raw[8];
    int temp_c = (temp_f-32)*5/9; /* Convert Fahrenheit to Celsius. */

    fieldset_add_bytes(info->fieldset,"Tire ID",raw+4,3*2);
    fieldset_add_float(info->fieldset,"Pressure kpa",kpa,2);
    fieldset_add_int(info->fieldset,"Temperature C",temp_c,8);
    return true;
}

ProtoViewDecoder SchraderEG53MA4TPMSDecoder = {
    .name = "Schrader EG53MA4 TPMS",
    .decode = decode,
    .get_fields = NULL,
    .build_message = NULL
};