Enhance Kedsum with MIC, model changed to "Kedsum-TH"

src/devices/kedsum.c

@@ -1,31 +1,53 @@
-/* Kedsum temperature and humidity sensor (http://amzn.to/25IXeng)
-   My models transmit at a bit lower freq. Around ~433.71 Mhz
-
-   Copyright (C) 2016 John Lifsey
-
-   This program is free software; you can redistribute it and/or modify
-   it under the terms of the GNU General Public License version 3 as
-   published by the Free Software Foundation.
-
-   Largely based on prologue, esperanza_ews, s3318p
-   Frame appears to be a differently-endianed version of the esperanza
-
-   Frame structure:
-   IIIIIIII????CC++++ttttTTTThhhhHHHH?????? PP
-
-   IIIIIIII unique id. changes on powercycle
-   CC channel, 00 = ch1, 10=ch3
-   ++++ low temp nibble
-   tttt med temp nibble
-   TTTT high temp nibble
-   hhhh humidity low nibble
-   HHHH humidity high nibble
+/** @file
+    Kedsum temperature and humidity sensor (http://amzn.to/25IXeng).
+    My models transmit at a bit lower freq. of around 433.71 Mhz.
+    Also NC-7415 from Pearl.
+
+    Copyright (C) 2016 John Lifsey
+    Enhanced (C) 2019 Christian W. Zuckschwerdt <zany@triq.net>
+
+    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.
+*/
+/**
+Largely based on prologue, esperanza_ews, s3318p.
+Frame appears to be a differently-endianed version of the esperanza.
+
+Frame structure:
+
+        00 IIIIIIII BBCC++++ ttttTTTT hhhhHHHH FFFFXXXX
+
+- IIIIIIII: unique id. changes on powercycle
+- BB: Battery state 10 = Ok, 01 = weak, 00 = bad
+- CC: channel, 00 = ch1, 10=ch3
+- ++++: low temp nibble
+- tttt: med temp nibble
+- TTTT: high temp nibble
+- hhhh: humidity low nibble
+- HHHH: humidity high nibble
+- FFFF: flags
+- XXXX: LFSR-4 (simple, not digest), static key 0x3
 */
 
 #include "decoder.h"
 
+static uint8_t lfsr4(uint8_t const message[], unsigned nBits, uint8_t key)
+{
+    int sum = 0;
+    for (unsigned i = 0; i < nBits; i++) {
+        if (i % 8 == 0)
+            sum |= *message++;
+        sum <<= 1;
+        if (sum & 0x1000)
+            sum ^= key << 8;
+    }
+    return (sum & 0xf00) >> 8;
+}
+
 static int kedsum_callback(r_device *decoder, bitbuffer_t *bitbuffer) {
-    bitrow_t *bb = bitbuffer->bb;
+    uint8_t b[5];
     data_t *data;
 
     // the signal should start with 15 sync pulses (empty rows)
@@ -41,44 +63,32 @@ static int kedsum_callback(r_device *decoder, bitbuffer_t *bitbuffer) {
     // the signal should have 6 repeats with a sync pulse between
     // require at least 4 received repeats
     int r = bitbuffer_find_repeated_row(bitbuffer, 4, 42);
-    if (r<0 || bitbuffer->bits_per_row[r] != 42)
+    if (r < 0 || bitbuffer->bits_per_row[r] != 42)
         return 0;
 
-    uint8_t *b = bb[r];
-
-    uint8_t humidity;
-    uint8_t channel;
-    uint16_t temperature_with_offset;
-    float temperature_f;
-
-    channel  = (uint8_t)(((b[1] & 0x0C) >> 2) + 1);
-    humidity = (uint8_t)((b[3] & 0x03) << 6) | ((b[4] & 0xC0) >> 2) | ((b[3] & 0x3C) >> 2);
-
-    uint8_t tnH, tnM, tnL;
-    tnL = ((b[1] & 0x03) << 2) | ((b[2] & 0xC0) >> 6); // Low temp nibble
-    tnM = ((b[2] & 0x3C) >> 2);                        // Med temp nibble
-    tnH = ((b[2] & 0x03) << 2) | ((b[3] & 0xC0) >> 6); // high temp nibble
-
-    temperature_with_offset =  (tnH<<8) | (tnM<<4) | tnL;
-    temperature_f = (temperature_with_offset - 900) / 10.0;
-
-    if (decoder->verbose) {
-      fprintf(stdout, "Bitstream HEX        = ");
-      bitrow_print(b, 48);
-      fprintf(stdout, "Humidity HEX         = %02x\n", b[3]);
-      fprintf(stdout, "Humidity DEC         = %u\n",   humidity);
-      fprintf(stdout, "Channel HEX          = %02x\n", b[1]);
-      fprintf(stdout, "Channel              = %u\n",   channel);
-      fprintf(stdout, "temp_with_offset HEX = %02x\n", temperature_with_offset);
-      fprintf(stdout, "temp_with_offset     = %d\n",   temperature_with_offset);
-      fprintf(stdout, "TemperatureF         = %.1f\n", temperature_f);
-    }
+    // remove the two leading 0-bits and align the data
+    bitbuffer_extract_bytes(bitbuffer, r, 2, b, 40);
+    int chk = lfsr4(b, 36, 0x3);
+    if (chk != (b[4] & 0xf))
+        return 0;
+
+    int id       = b[0];
+    int battery  = b[1] >> 6;
+    int channel  = ((b[1] & 0x30) >> 4) + 1;
+    int humidity = ((b[3] & 0xf0) >> 4) | ((b[3] & 0x0f) << 4);
+    int temp_raw = ((b[1] & 0x0f) << 0) | ((b[2] & 0xf0) << 0) | ((b[2] & 0x0f) << 8);
+    float temp_f = (temp_raw - 900) * 0.1;
+
+    char *battery_str = battery == 2 ? "OK" : battery == 1 ? "WEAK" : "LOW";
 
     data = data_make(
-            "model",         "",            DATA_STRING, "Kedsum Temperature & Humidity Sensor",
-            "channel",       "Channel",     DATA_INT, channel,
-            "temperature_F", "Temperature", DATA_FORMAT, "%.02f F", DATA_DOUBLE, temperature_f,
-            "humidity",      "Humidity",    DATA_FORMAT, "%u %%", DATA_INT, humidity,
+            "model",            "",             DATA_STRING, "Kedsum-TH",
+            "id",               "ID",           DATA_INT, id,
+            "channel",          "Channel",      DATA_INT, channel,
+            "battery",          "Battery",      DATA_STRING, battery_str,
+            "temperature_F",    "Temperature",  DATA_FORMAT, "%.02f F", DATA_DOUBLE, temp_f,
+            "humidity",         "Humidity",     DATA_FORMAT, "%u %%", DATA_INT, humidity,
+            "mic",              "Integrity",    DATA_STRING, "CRC",
             NULL);
 
     decoder_output_data(decoder, data);
@@ -87,14 +97,17 @@ static int kedsum_callback(r_device *decoder, bitbuffer_t *bitbuffer) {
 
 static char *output_fields[] = {
     "model",
+    "id",
     "channel",
+    "battery",
     "temperature_F",
     "humidity",
+    "mic",
     NULL
 };
 
 r_device kedsum = {
-    .name           = "Kedsum Temperature & Humidity Sensor",
+    .name           = "Kedsum Temperature & Humidity Sensor, Pearl NC-7415",
     .modulation     = OOK_PULSE_PPM,
     .short_width    = 2000,
     .long_width     = 4000,