Momentum-Apps/protocols/tpms/ford.c

/* Ford tires TPMS. Usually 443.92 Mhz FSK (in Europe).
 *
 * 52 us short pules
 * Preamble: 0101010101010101010101010101
 * Sync: 0110 (that is 52 us gap + 104 us pulse + 52 us gap)
 * Data: 8 bytes Manchester encoded
 * 01 = zero
 * 10 = one
 */

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

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

    const char *sync_pattern = "010101010101" "0110";
    uint8_t sync_len = 12+4; /* We just use 12 preamble symbols + sync. */
    if (numbits-sync_len < 8*8) 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, "Fort TPMS preamble+sync found");

    info->start_off = off;
    off += sync_len; /* Skip preamble and sync. */

    uint8_t raw[8];
    uint32_t decoded =
        convert_from_line_code(raw,sizeof(raw),bits,numbytes,off,
            "01","10"); /* Manchester. */
    FURI_LOG_E(TAG, "Ford TPMS decoded bits: %lu", decoded);

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

    /* CRC is just the sum of the first 7 bytes MOD 256. */
    uint8_t crc = 0;
    for (int j = 0; j < 7; j++) crc += raw[j];
    if (crc != raw[7]) return false; /* Require sane CRC. */

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

    float psi = 0.25 * (((raw[6]&0x20)<<3)|raw[4]);

    /* Temperature apperas to be valid only if the most significant
     * bit of the value is not set. Otherwise its meaning is unknown.
     * Likely useful to alternatively send temperature or other info. */
    int temp = raw[5] & 0x80 ? 0 : raw[5]-56;
    int flags = raw[5] & 0x7f;
    int car_moving = (raw[6] & 0x44) == 0x44;

#if 0
    snprintf(info->name,sizeof(info->name),"%s","Ford TPMS");
    snprintf(info->raw,sizeof(info->raw),"%02X%02X%02X%02X%02X%02X%02X%02X",
        raw[0],raw[1],raw[2],raw[3],raw[4],raw[5],
        raw[6],raw[7]);
    snprintf(info->info1,sizeof(info->info1),"Tire ID %02X%02X%02X%02X",
        raw[0],raw[1],raw[2],raw[3]);
    snprintf(info->info2,sizeof(info->info2),"Pressure %.2f psi", (double)psi);
    if (temp)
        snprintf(info->info3,sizeof(info->info3),"Temperature %d C", temp);
    else
        snprintf(info->info3,sizeof(info->info3),"Flags %d", flags);
    snprintf(info->info4,sizeof(info->info4),"Moving %s", car_moving ? "yes" : "no");
#endif
    return true;
}

ProtoViewDecoder FordTPMSDecoder = {
    .name = "Ford TPMS",
    .decode = decode,
    .get_fields = NULL,
    .build_message = NULL
};