From 29b14b4dc6fcd0980cf0adf8bac8bebd55b6bbab Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Robert=20H=C3=B6gberg?= <robert.hogberg@gmail.com>
Date: Mon, 24 Jan 2022 05:15:52 +0100
Subject: [PATCH] Change wt0124 to use additional checksum (#1959)

---
 src/devices/wt0124.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/src/devices/wt0124.c b/src/devices/wt0124.c
index 062b75af..2efd3481 100644
--- a/src/devices/wt0124.c
+++ b/src/devices/wt0124.c
@@ -12,9 +12,9 @@
 /**
 WT0124 Pool Thermometer decoder.
 
-    5e       ba       9a       9f       e1       34
-    01011110 10111010 10011010 10011111 11100001 00110100
-    5555RRRR RRRRTTTT TTTTTTTT UUCCFFFF XXXXXXXX ????????
+    5e       ba       9a       9f       e1       34       1
+    01011110 10111010 10011010 10011111 11100001 00110100 1
+    5555RRRR RRRRTTTT TTTTTTTT UUCCFFFF XXXXXXXX SSSSSSSS 1
 
 - 5 = constant 5
 - R = random power on id
@@ -23,8 +23,8 @@ WT0124 Pool Thermometer decoder.
 - C = channel
 - F = constant F
 - X = xor checksum
-- ? = unknown
-
+- S = sum checksum
+- 1 = constant 1
 */
 
 #include "decoder.h"
@@ -33,8 +33,8 @@ static int wt1024_callback(r_device *decoder, bitbuffer_t *bitbuffer)
 {
     data_t *data;
     uint8_t *b; // bits of a row
+    uint16_t sum;
     uint16_t sensor_rid;
-    int16_t value;
     float temp_c;
     uint8_t channel;
 
@@ -49,10 +49,20 @@ static int wt1024_callback(r_device *decoder, bitbuffer_t *bitbuffer)
         return DECODE_ABORT_EARLY;
     }
 
-    /* Validate checksum */
+    /* Validate xor checksum */
     if (xor_bytes(b, 4) != b[4])
         return DECODE_FAIL_MIC;
 
+    /* Validate sum checksum */
+    sum = add_bytes(b, 4);
+    /* Carry bits are added to the sum .. */
+    sum += sum >> 8;
+    /* .. but no carry bit is added to the sum from the last addition */
+    sum += b[4];
+    sum &= 0xFF;
+    if (sum != b[5])
+        return DECODE_FAIL_MIC;
+
     /* Get rid */
     sensor_rid = (b[0] & 0x0F) << 4 | (b[1] & 0x0F);
 
@@ -62,9 +72,6 @@ static int wt1024_callback(r_device *decoder, bitbuffer_t *bitbuffer)
     /* Get channel */
     channel = (b[3] >> 4) & 0x3;
 
-    /* unk */
-    value = b[5];
-
     if (decoder->verbose) {
         fprintf(stderr, "wt1024_callback:");
         bitbuffer_print(bitbuffer);
@@ -76,7 +83,6 @@ static int wt1024_callback(r_device *decoder, bitbuffer_t *bitbuffer)
             "id",               "Random ID",    DATA_INT,    sensor_rid,
             "channel",          "Channel",      DATA_INT,    channel,
             "temperature_C",    "Temperature",  DATA_FORMAT, "%.1f C", DATA_DOUBLE, temp_c,
-            "data",             "Data",         DATA_INT,    value,
             "mic",              "Integrity",    DATA_STRING, "CHECKSUM",
             NULL);
     /* clang-format on */
@@ -99,7 +105,6 @@ static char *output_fields[] = {
         "id",
         "channel",
         "temperature_C",
-        "data",
         "mic",
         NULL,
 };