Fix Steelmate pressure formula

src/devices/steelmate.c

@@ -3,6 +3,7 @@
 
     Copyright (C) 2016 Benjamin Larsson
     Copyright (C) 2016 John Jore
+    Copyright (C) 2025 Bruno OCTAU (ProfBoc75)
 
     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
@@ -12,7 +13,23 @@
 /**
 Steelmate TPMS FSK protocol.
 
-Packet payload: 9 bytes.
+Reference:
+
+- model TP-S15
+
+Brand:
+
+- Steelmate
+- R-Lake
+
+S.a. issue #3200 Pressure issue :
+
+- The originally guessed formula was : Pressure in PSI scale 2, but more the pressure is important more the value diverged between the TPMS display and rtl_433.
+- New analysis : Based on data collected by \@e100 + the technical specification ( 0~7.9Bar ) + analysis by \@e100 and refined by \@ProfBoc75, the pressure is given in Bar at scale 32.
+
+Packet payload:
+
+- 9 bytes.
 
 Bytes 2 to 9 are inverted Manchester with swapped MSB/LSB:
 
@@ -24,9 +41,12 @@ Bytes 2 to 9 are inverted Manchester with swapped MSB/LSB:
 - S = sync, (0x00)
 - A = preamble, (0x01)
 - I = id, 0xc3f0
-- P = Pressure as double the PSI, 0x14 = 10 PSI
-- T = Temperature in Fahrenheit, 0x4a = 74 'F
-- B = Battery as half the millivolt, 0x8e = 2.84 V
+- P = Pressure in Bar, scale 32, 0xA0 / 32 = 5 Bar, or 0xA0 * 3.125 = 500 kPA, see issue #3200
+- T = Temperature in Celcius + 50, 0x4a = 24 'C
+- B = Battery, where mV = 3900-(value*10). E.g 0x8e becomes 3900-(1420) = 2480mV.
+-     This calculation is approximate fit from sample data, any improvements are welcome.
+-   > If this field is set to 0xFF, a "fast leak" alarm is triggered.
+-   > If this field is set to 0xFE, a "slow leak" alarm is triggered.
 - C = Checksum, adding bytes 2 to 7 modulo 256 = byte 8,(0x01+0xc3+0xf0+0x14+0x4a+0x8e) modulus 256 = 0xa0
 
 */
@@ -35,58 +55,61 @@ Bytes 2 to 9 are inverted Manchester with swapped MSB/LSB:
 
 static int steelmate_callback(r_device *decoder, bitbuffer_t *bitbuffer)
 {
+    uint8_t const preamble_pattern[] = {0x00, 0x00, 0x7f}; // inverted, raw value is 0x5a
     //Loop through each row of data
-    for (int row = 0; row < bitbuffer->num_rows; row++)
-    {
+    for (int row = 0; row < bitbuffer->num_rows; row++) {
         //Payload is inverted Manchester encoded, and reversed MSB/LSB order
-        uint8_t *b = bitbuffer->bb[row];
+        unsigned row_len = bitbuffer->bits_per_row[row];
 
-        //Length must be 72 bits to be considered a valid packet
-        if (bitbuffer->bits_per_row[row] != 72)
+        //Length must be 72, 73, 208 or 209 bits to be considered a valid packet
+        if (row_len != 72 && row_len != 73 && row_len != 209 && row_len != 208)
             continue; // DECODE_ABORT_LENGTH
 
         //Valid preamble? (Note, the data is still wrong order at this point. Correct pre-amble: 0x00 0x00 0x01)
-        if (b[0] != 0x00 || b[1] != 0x00 || b[2] != 0x7f)
+        unsigned bitpos = bitbuffer_search(bitbuffer, row, 0, preamble_pattern, 24);
+        if (bitpos > row_len - 72)
             continue; // DECODE_ABORT_EARLY
+        bitbuffer_invert(bitbuffer);
+        uint8_t b[9];
+        bitbuffer_extract_bytes(bitbuffer, row, bitpos, b, 72);
 
-        //Preamble
-        uint8_t preamble = ~reverse8(b[2]);
+        reflect_bytes(b, 9);
 
-        //Sensor ID
-        uint8_t id1 = ~reverse8(b[3]);
-        uint8_t id2 = ~reverse8(b[4]);
+        //Checksum is a sum of all the other values
+        if ((add_bytes(&b[2], 6) & 0xFF) != b[8])
+            continue; // DECODE_FAIL_MIC
 
-        //Pressure is stored as twice the PSI
-        uint8_t p1 = ~reverse8(b[5]);
+        //Sensor ID
+        uint8_t id1 = b[3];
+        uint8_t id2 = b[4];
 
-        //Temperature is stored in Fahrenheit. Note that the datasheet claims operational to -40'C, but can only express values from -17.8'C
-        uint8_t tempFahrenheit = ~reverse8(b[6]);
+        //Pressure is stored as 32 * the Bar
+        uint8_t p1 = b[5];
 
-        //Battery voltage is stored as half the mV
-        uint8_t tmpbattery_mV = ~reverse8(b[7]);
+        //Temperature is sent as degrees Celcius + 50.
+        int temp_c = b[6] - 50;
 
-        //Checksum is a sum of all the other values
-        uint8_t payload_checksum = ~reverse8(b[8]);
-        uint8_t calculated_checksum = preamble + id1 + id2 + p1 + tempFahrenheit + tmpbattery_mV;
-        if (payload_checksum != calculated_checksum)
-            continue; // DECODE_FAIL_MIC
+        //Battery voltage is stored as 100*(3.9v-<volt>).
+        uint8_t b1     = b[7];
+        int battery_mv = 3900 - b1 * 10;
 
         int sensor_id      = (id1 << 8) | id2;
-        float pressure_psi = p1 * 0.5f;
-        int battery_mV     = tmpbattery_mV * 2;
+        float pressure_kpa = p1 * 3.125f;                         // as guessed in #3200
 
         char sensor_idhex[7];
         snprintf(sensor_idhex, sizeof(sensor_idhex), "0x%04x", sensor_id);
 
         /* clang-format off */
         data_t *data = data_make(
-                "type",             "",             DATA_STRING, "TPMS",
-                "model",            "",             DATA_STRING, "Steelmate",
-                "id",               "",             DATA_STRING, sensor_idhex,
-                "pressure_PSI",     "",             DATA_DOUBLE, pressure_psi,
-                "temperature_F",    "",             DATA_DOUBLE, (float)tempFahrenheit,
-                "battery_mV",       "",             DATA_INT,    battery_mV,
-                "mic",              "Integrity",    DATA_STRING, "CHECKSUM",
+                "type",             "",             DATA_STRING,  "TPMS",
+                "model",            "",             DATA_STRING,  "Steelmate",
+                "id",               "",             DATA_STRING,  sensor_idhex,
+                "pressure_kPa",     "",             DATA_FORMAT,  "%.0f kPa", DATA_DOUBLE,  pressure_kpa,
+                "temperature_C",    "",             DATA_FORMAT,  "%d C",     DATA_INT,     temp_c,
+                "battery_mV",       "",             DATA_COND,    b1 < 0xFE,  DATA_INT,     battery_mv,
+                "alarm",            "",             DATA_COND,    b1 == 0xFF, DATA_STRING, "fast leak",
+                "alarm",            "",             DATA_COND,    b1 == 0xFE, DATA_STRING, "slow leak",
+                "mic",              "Integrity",    DATA_STRING,  "CHECKSUM",
                 NULL);
         /* clang-format on */
 
@@ -103,19 +126,20 @@ static char const *const output_fields[] = {
         "type",
         "model",
         "id",
-        "pressure_PSI",
-        "temperature_F",
+        "pressure_kPa",
+        "temperature_C",
         "battery_mV",
+        "alarm",
         "mic",
         NULL,
 };
 
 r_device const steelmate = {
         .name        = "Steelmate TPMS",
         .modulation  = FSK_PULSE_MANCHESTER_ZEROBIT,
-        .short_width = 12 * 4,
-        .long_width  = 0,
-        .reset_limit = 27 * 4,
+        .short_width = 50,
+        .long_width  = 50,
+        .reset_limit = 120,
         .decode_fn   = &steelmate_callback,
         .fields      = output_fields,
 };