Add General Motors TPMS

conf/rtl_433.example.conf

@@ -504,6 +504,7 @@ convert si
   protocol 272 # Landis & Gyr Gridstream Power Meters 19.2k
   protocol 273 # Landis & Gyr Gridstream Power Meters 38.4k
   protocol 274 # Revolt ZX-7717 power meter
+  protocol 275 # GM TPMS
 
 ## Flex devices (command line option "-X")
 

include/rtl_433_devices.h

@@ -282,6 +282,7 @@
     DECL(gridstream192) \
     DECL(gridstream384) \
     DECL(revolt_zx7717) \
+    DECL(tpms_gm) \
 
     /* Add new decoders here. */
 

src/CMakeLists.txt

@@ -254,6 +254,7 @@ add_library(r_433 STATIC
     devices/tpms_eezrv.c
     devices/tpms_elantra2012.c
     devices/tpms_ford.c
+    devices/tpms_gm.c
     devices/tpms_hyundai_vdo.c
     devices/tpms_jansite.c
     devices/tpms_jansite_solar.c

src/devices/tpms_gm.c

@@ -0,0 +1,161 @@
+/** @file
+    General Motors Aftermarket TPMS
+
+    Copyright (C) 2025 Eric Blevins
+
+    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.
+*/
+
+#include "decoder.h"
+#include "r_util.h"
+#include <stdio.h>
+#include <inttypes.h>  // Needed for PRIX64
+
+static uint8_t const preamble_pattern[6] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+
+/**
+Data was detected an initially captured using:
+
+  rtl_433 -X 'n=name,m=OOK_MC_ZEROBIT,s=120,l=0,r=15600'
+
+These sensors react to a signal from an EL-50448 relearn tool.
+They enter into learn mode upon receiving the signal and transmit.
+If they remain at 0PSI they will not transmit unless receiving signal
+from the relearn tool.
+If they have pressure they transmit every 2 minutes and will exit
+the learn mode after one cycle.
+Any sudden changes in pressure triggers immediate signal.
+These do not seem capable of detection motion.
+
+
+
+130 bits
+AAAAAAAAAAAASSSSDDDDIIIIIIPPTTCCX
+0000000000004c90007849176600536d0
+ Data layout:
+
+   AAAAAAAAAAAASSSSDDDDIIIIIIPPTTCCX
+
+- A: preamble 0x000000000000
+- S: Status
+- D: Device type or prefix
+- I: Device uniquie identifier
+- P: Pressure
+- T: Temperature
+- C: CheckSum, modulo 256
+
+The only status data detected is learn mode and low battery.
+Bit 5 of status indicates low battery when set to 1
+Bits 0,1,8 are set to 0 to indicate learn mode and 1 for operational mode.
+The sensors drop to learn mode when detecting a large pressure drop
+or when activated with the learning tool
+
+In learn mode with zero pressure they only transmit when activated by
+the learning tool.
+Once presurized they will transmit in learn mode and within a couple
+minutes switch to sending in operatioinal mode every teo minutes.
+
+*/
+
+static int tpms_gm_decode(r_device *decoder, bitbuffer_t *bitbuffer)
+{
+    if (bitbuffer->num_rows != 1) {
+        return DECODE_ABORT_EARLY;
+    }
+
+    if (bitbuffer->bits_per_row[0] != 130) {
+        return DECODE_ABORT_LENGTH;
+    }
+
+    int pos = bitbuffer_search(bitbuffer, 0, 0, preamble_pattern, sizeof(preamble_pattern) * 8);
+    if (pos < 0) {
+        return DECODE_ABORT_EARLY;
+    }
+
+    // Buffer for extracted bytes
+    uint8_t b[17] = {0};
+    bitbuffer_extract_bytes(bitbuffer, 0, 0, b, 130);
+
+    // Checksum skips preamble
+    uint8_t computed_checksum = 0;
+    for (int i = 6; i < 15; i++) {
+        computed_checksum += b[i];
+    }
+    if ((computed_checksum % 256) != b[15]) {
+        return DECODE_FAIL_MIC;
+    }
+
+    // Convert ID to an integer
+    uint64_t sensor_id = ((uint64_t)b[8] << 32) | ((uint64_t)b[9] << 24) | (b[10] << 16) | (b[11] << 8) | b[12];
+    uint16_t status = (b[6] << 8) | b[7];
+
+    uint8_t pressure_raw = b[13];
+    uint8_t temperature_raw = b[14];
+
+    // Adding 3.75 made my sensors accurate accurate
+    // But I think it might be best to allow the user to
+    // to add their own offset when consuming the data
+    float pressure_kpa = (pressure_raw * 2.75);
+    float pressure_psi = kpa2psi(pressure_kpa);
+    float temperature_c = temperature_raw - 60;
+
+    // Extract bits correctly based on little-endian order
+    int bit8 = (status >> 8) & 1;
+    int bit1 = (status >> 1) & 1;
+    int bit0 = (status >> 0) & 1;
+
+    // Status bits
+    int learn_mode = ((bit8 == 0) && (bit1 == 0) && (bit0 == 0)) ? 1 : 0;
+    int battery_ok = !((status >> 5) & 1);
+
+    char status_hex[7];  // 6 chars + null terminator for "0xFFFF"
+    snprintf(status_hex, sizeof(status_hex), "0x%04X", status);
+
+    /* clang-format off */
+    data_t *data = data_make(
+        "model",           "",            DATA_STRING,  "GM Aftermarket TPMS",
+        "type",            "",            DATA_STRING,  "TPMS",
+        "id",              "",            DATA_INT,     sensor_id,
+        "status",          "",            DATA_STRING,  status_hex,
+        "learn_mode",      "",            DATA_INT,     learn_mode,
+        "battery_ok",      "",            DATA_INT,     battery_ok,
+        "pressure_kPa",    "",            DATA_DOUBLE,  pressure_kpa,
+        "pressure_PSI",    "",            DATA_DOUBLE,  pressure_psi,
+        "temperature_C",   "",            DATA_DOUBLE,  temperature_c,
+        "mic",             "Integrity",   DATA_STRING,  "CHECKSUM",
+        NULL);
+
+    /* clang-format on */
+
+    decoder_output_data(decoder, data);
+    return 1;
+}
+
+/** Output fields for rtl_433 */
+static char const *const output_fields[] = {
+    "model",
+    "type",
+    "id",
+    "status",
+    "learn_mode",
+    "battery_ok",
+    "pressure_kPa",
+    "pressure_PSI",
+    "temperature_C",
+    "mic",
+    NULL,
+};
+
+r_device const tpms_gm = {
+    .name        = "GM Aftermarket TPMS",
+    .modulation  = OOK_PULSE_MANCHESTER_ZEROBIT,
+    .short_width = 120,
+    .long_width  = 0,
+    .reset_limit = 15600,
+    .decode_fn   = &tpms_gm_decode,
+    .fields      = output_fields,
+};
+