Merge pull request 'TMP1075 two's complement bugfix' (#681) from tmp-sign-bugfix into main

Reviewed-on: #681
Reviewed-by: Marius Eggert <eggertm@irs.uni-stuttgart.de>

CHANGELOG.md

@@ -18,6 +18,13 @@ will consitute of a breaking change warranting a new major release:
 
 # [v4.0.0] to be released
 
+# [v3.1.1] 2023-06-14
+
+## Fixed
+
+- TMP1075 bugfix where negative temperatures could not be measured because of a two's-complement
+  conversion bug.
+
 # [v3.1.0] 2023-06-14
 
 - `eive-tmtc` version v4.1.0

mission/tcs/Tmp1075Handler.cpp

@@ -86,8 +86,11 @@ ReturnValue_t Tmp1075Handler::scanForReply(const uint8_t *start, size_t remainin
 ReturnValue_t Tmp1075Handler::interpretDeviceReply(DeviceCommandId_t id, const uint8_t *packet) {
   switch (id) {
     case TMP1075::GET_TEMP: {
-      int16_t tempValueRaw = 0;
-      tempValueRaw = packet[0] << 4 | packet[1] >> 4;
+      // Convert 12 bit MSB first raw temperature to 16 bit first.
+      int16_t tempValueRaw = static_cast<uint16_t>((packet[0] << 8) | packet[1]) >> 4;
+      // Sign extension to 16 bits: If the sign bit is set, fill up with ones on the left.
+      tempValueRaw = (packet[0] & 0x80) ? (tempValueRaw | 0xF000) : tempValueRaw;
+      // 0.0625 is the sensor sensitivity.
       float tempValue = ((static_cast<float>(tempValueRaw)) * 0.0625);
 #if OBSW_DEBUG_TMP1075 == 1
       sif::info << "Tmp1075 with object id: 0x" << std::hex << getObjectId()