rtl_433/src/devices/radiohead_ask.c

/** @file
    RadioHead ASK (generic) protocol.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
*/
/** @fn int radiohead_ask_callback(r_device *decoder, bitbuffer_t *bitbuffer)
RadioHead ASK (generic) protocol.

Default transmitter speed is 2000 bits per second, i.e. 500 us per bit.
The symbol encoding ensures a maximum run (gap) of 4x bit-width.
Sensible Living uses a speed of 1000, i.e. 1000 us per bit.
*/

#include "decoder.h"

// Maximum message length (including the headers, byte count and FCS) we are willing to support
// This is pretty arbitrary
#define RH_ASK_MAX_PAYLOAD_LEN 67
#define RH_ASK_HEADER_LEN 4
#define RH_ASK_MAX_MESSAGE_LEN (RH_ASK_MAX_PAYLOAD_LEN - RH_ASK_HEADER_LEN - 3)

// Note: all the "4to6 code" came from RadioHead source code.
// see: http://www.airspayce.com/mikem/arduino/RadioHead/index.html

// 4 bit to 6 bit symbol converter table
// Used to convert the high and low nybbles of the transmitted data
// into 6 bit symbols for transmission. Each 6-bit symbol has 3 1s and 3 0s
// with at most 3 consecutive identical bits.
// Concatenated symbols have runs of at most 4 identical bits.
static uint8_t const symbols[] = {
        0x0d, 0x0e, 0x13, 0x15, 0x16, 0x19, 0x1a, 0x1c,
        0x23, 0x25, 0x26, 0x29, 0x2a, 0x2c, 0x32, 0x34
};

// Convert a 6 bit encoded symbol into its 4 bit decoded equivalent
static uint8_t symbol_6to4(uint8_t symbol)
{
    uint8_t i;
    // Linear search :-( Could have a 64 byte reverse lookup table?
    // There is a little speedup here courtesy Ralph Doncaster:
    // The shortcut works because bit 5 of the symbol is 1 for the last 8
    // symbols, and it is 0 for the first 8.
    // So we only have to search half the table
    for (i = (symbol >> 2) & 8; i < 16; i++) {
        if (symbol == symbols[i])
            return i;
    }
    return 0xFF; // Not found
}

/**
Radiohead ASK parser.
*/
static int radiohead_ask_extract(r_device *decoder, bitbuffer_t *bitbuffer, uint8_t row, /*OUT*/ uint8_t *payload)
{
    int len = bitbuffer->bits_per_row[row];
    int msg_len = RH_ASK_MAX_MESSAGE_LEN;
    int pos, nb_bytes;
    uint8_t rxBits[2] = {0};

    uint16_t crc, crc_recompute;

    // Looking for preamble
    uint8_t const init_pattern[] = {
            0x55, // 8
            0x55, // 16
            0x55, // 24
            0x51, // 32
            0xcd, // 40
    };
    // The first 0 is ignored by the decoder, so we look only for 28 bits of "01"
    // and not 32. Also "0x1CD" is 0xb38 (RH_ASK_START_SYMBOL) with LSBit first.
    int init_pattern_len = 40;

    pos = bitbuffer_search(bitbuffer, row, 0, init_pattern, init_pattern_len);
    if (pos == len) {
        decoder_log(decoder, 2, __func__, "preamble not found");
        return DECODE_ABORT_EARLY;
    }

    // read "bytes" of 12 bit
    nb_bytes = 0;
    pos += init_pattern_len;
    for (; pos < len && nb_bytes < msg_len; pos += 12) {
        bitbuffer_extract_bytes(bitbuffer, row, pos, rxBits, /*len=*/16);
        // ^ we should read 16 bits and not 12, elsewhere last 4bits are ignored
        rxBits[0] = reverse8(rxBits[0]);
        rxBits[1] = reverse8(rxBits[1]);
        rxBits[1] = ((rxBits[1] & 0x0F) << 2) + (rxBits[0] >> 6);
        rxBits[0] &= 0x3F;
        uint8_t hi_nibble = symbol_6to4(rxBits[0]);
        if (hi_nibble > 0xF) {
            decoder_logf(decoder, 1, __func__, "Error on 6to4 decoding high nibble: %X", rxBits[0]);
            return DECODE_FAIL_SANITY;
        }
        uint8_t lo_nibble = symbol_6to4(rxBits[1]);
        if (lo_nibble > 0xF) {
            decoder_logf(decoder, 1, __func__, "Error on 6to4 decoding low nibble: %X", rxBits[1]);
            return DECODE_FAIL_SANITY;
        }
        uint8_t byte = hi_nibble << 4 | lo_nibble;
        payload[nb_bytes] = byte;
        if (nb_bytes == 0) {
            msg_len = byte;
            // abort on invalid message length byte
            if (msg_len < 2 || msg_len > RH_ASK_MAX_MESSAGE_LEN) {
                break;
            }
        }
        nb_bytes++;
    }

    // Prevent buffer underflow when calculating CRC
    if (msg_len < 2) {
        decoder_log(decoder, 2, __func__, "message too short to contain crc");
        return DECODE_ABORT_LENGTH;
    }
    // Sanity check on excessive msg len
    if (msg_len > RH_ASK_MAX_MESSAGE_LEN) {
        decoder_logf(decoder, 2, __func__, "message too long: %d", msg_len);
        return DECODE_ABORT_LENGTH;
    }

    // Check CRC
    crc = (payload[msg_len - 1] << 8) | payload[msg_len - 2];
    crc_recompute = ~crc16lsb(payload, msg_len - 2, 0x8408, 0xFFFF);
    if (crc_recompute != crc) {
        decoder_logf(decoder, 1, __func__, "CRC error: %04X != %04X", crc_recompute, crc);
        return DECODE_FAIL_MIC;
    }

    return msg_len;
}

static int radiohead_ask_callback(r_device *decoder, bitbuffer_t *bitbuffer)
{
    data_t *data;
    uint8_t row = 0; // we are considering only first row
    int msg_len, data_len, header_to, header_from, header_id, header_flags;

    uint8_t rh_payload[RH_ASK_MAX_PAYLOAD_LEN] = {0};
    int rh_data_payload[RH_ASK_MAX_MESSAGE_LEN];

    msg_len = radiohead_ask_extract(decoder, bitbuffer, row, rh_payload);
    if (msg_len <= 0) {
        return msg_len; // pass error code on
    }
    data_len = msg_len - RH_ASK_HEADER_LEN - 3;
    if (data_len <= 0)
        return DECODE_FAIL_SANITY;

    header_to    = rh_payload[1];
    header_from  = rh_payload[2];
    header_id    = rh_payload[3];
    header_flags = rh_payload[4];

    // Format data
    for (int j = 0; j < data_len; j++) {
        rh_data_payload[j] = (int)rh_payload[5 + j];
    }
    /* clang-format off */
    data = data_make(
            "model",        "",             DATA_STRING, "RadioHead-ASK",
            "len",          "Data len",     DATA_INT, data_len,
            "to",           "To",           DATA_INT, header_to,
            "from",         "From",         DATA_INT, header_from,
            "id",           "Id",           DATA_INT, header_id,
            "flags",        "Flags",        DATA_INT, header_flags,
            "payload",      "Payload",      DATA_ARRAY, data_array(data_len, DATA_INT, rh_data_payload),
            "mic",          "Integrity",    DATA_STRING, "CRC",
            NULL);
    /* clang-format on */

    decoder_output_data(decoder, data);
    return 1;
}

/**
Sensible Living Mini-Plant Moisture Sensor.

@todo Documentation needed.
*/
static int sensible_living_callback(r_device *decoder, bitbuffer_t *bitbuffer)
{
    data_t *data;
    uint8_t row = 0; // we are considering only first row
    int msg_len, house_id, sensor_type, sensor_count, alarms;
    int module_id, sensor_value, battery_voltage;

    uint8_t rh_payload[RH_ASK_MAX_PAYLOAD_LEN] = {0};

    msg_len = radiohead_ask_extract(decoder, bitbuffer, row, rh_payload);
    if (msg_len <= 0) {
        return msg_len; // pass error code on
    }

    house_id        = rh_payload[1];
    module_id       = (rh_payload[2] << 8) | rh_payload[3];
    sensor_type     = rh_payload[4];
    sensor_count    = rh_payload[5];
    alarms          = rh_payload[6];
    sensor_value    = (rh_payload[7] << 8) | rh_payload[8];
    battery_voltage = (rh_payload[9] << 8) | rh_payload[10];

    /* clang-format off */
    data = data_make(
            "model",            "",                 DATA_STRING,  "SensibleLiving-Moisture",
            "house_id",         "House ID",         DATA_INT,     house_id,
            "module_id",        "Module ID",        DATA_INT,     module_id,
            "sensor_type",      "Sensor Type",      DATA_INT,     sensor_type,
            "sensor_count",     "Sensor Count",     DATA_INT,     sensor_count,
            "alarms",           "Alarms",           DATA_INT,     alarms,
            "sensor_value",     "Sensor Value",     DATA_INT,     sensor_value,
            "battery_mV",       "Battery Voltage",  DATA_INT,     battery_voltage * 10,
            "mic",              "Integrity",        DATA_STRING,  "CRC",
            NULL);
    /* clang-format on */

    decoder_output_data(decoder, data);
    return 1;
}

static char const *const radiohead_ask_output_fields[] = {
        "model",
        "len",
        "to",
        "from",
        "id",
        "flags",
        "payload",
        "mic",
        NULL,
};

static char const *const sensible_living_output_fields[] = {
        "model",
        "house_id",
        "module_id",
        "sensor_type",
        "sensor_count",
        "alarms",
        "sensor_value",
        "battery_mV",
        "mic",
        NULL,
};

r_device const radiohead_ask = {
        .name        = "Radiohead ASK",
        .modulation  = OOK_PULSE_PCM,
        .short_width = 500,
        .long_width  = 500,
        .reset_limit = 5 * 500,
        .decode_fn   = &radiohead_ask_callback,
        .fields      = radiohead_ask_output_fields,
};

r_device const sensible_living = {
        .name        = "Sensible Living Mini-Plant Moisture Sensor",
        .modulation  = OOK_PULSE_PCM,
        .short_width = 1000,
        .long_width  = 1000,
        .reset_limit = 5 * 1000,
        .decode_fn   = &sensible_living_callback,
        .fields      = sensible_living_output_fields,
};