Fix NimBLEEddystoneTLM byte-order mismatch between getters and setters (#431)

* Fix NimBLEEddystoneTLM byte-order mismatch between getters and setters

m_eddystoneData must always hold Eddystone-TLM wire-format (big-endian)
bytes, since getData() returns it directly for the caller to memcpy
straight into the BLE advertisement payload (see the
BLE_EddystoneTLM_Beacon example), and setData()/getData() already treat
it as raw wire bytes.

The getters (getVolt/getTemp) correctly un-swap on read, but the
setters (setVolt/setTemp/setCount/setTime) stored their host-order
input directly with no swap, and the BeaconData default member
initializers were host-order values instead of pre-swapped wire-format
values. This breaks the setter/getter round trip for any value set
locally (as opposed to arriving over the air via setData()), and means
a freshly constructed object reports a garbage battery voltage.

toString() also failed to un-swap the temperature field at all, and
used unsigned division/modulo on a signed 8.8 fixed-point value,
producing garbage output for negative temperatures.

This mirrors the existing, correct pattern already used by the sibling
NimBLEBeacon class, which swaps in its setters (setMajor/setMinor/
setManufacturerId).

Fix:
- setVolt/setTemp/setCount/setTime now apply ENDIAN_CHANGE_U16/U32 to
  their input before storing, matching what the getters already
  assume.
- BeaconData's default volt/temp member initializers are now the
  wire-format (byte-swapped) encoding of the intended defaults (3300
  mV, 23.0C), so a freshly constructed object reports correct values
  without calling a setter first.
- toString() now swaps the temperature field the same way it already
  swaps voltage, and computes the displayed magnitude from a signed
  value with explicit sign handling instead of unsigned arithmetic on
  the raw field.

Author: 94xhn

src/NimBLEEddystoneTLM.cpp

@@ -101,10 +101,12 @@ std::string NimBLEEddystoneTLM::toString() {
     out += val;
     out += " mV\n";
 
-    out             += "Temperature ";
-    uint8_t intTemp  = m_eddystoneData.temp / 256;
-    uint8_t frac     = m_eddystoneData.temp % 256 * 100 / 256;
-    snprintf(val, sizeof(val), "%d.%d", intTemp, frac);
+    out              += "Temperature ";
+    int16_t  temp     = ENDIAN_CHANGE_U16(m_eddystoneData.temp);
+    uint32_t absTemp  = temp < 0 ? -static_cast<int32_t>(temp) : temp;
+    uint8_t  intTemp  = absTemp / 256;
+    uint8_t  frac     = absTemp % 256 * 100 / 256;
+    snprintf(val, sizeof(val), "%s%d.%02d", (temp < 0 ? "-" : ""), intTemp, frac);
     out += val;
     out += " C\n";
 
@@ -188,31 +190,31 @@ void NimBLEEddystoneTLM::setVersion(uint8_t version) {
  * @param [in] volt The voltage in millivolts.
  */
 void NimBLEEddystoneTLM::setVolt(uint16_t volt) {
-    m_eddystoneData.volt = volt;
+    m_eddystoneData.volt = ENDIAN_CHANGE_U16(volt);
 } // setVolt
 
 /**
  * @brief Set the temperature to advertise.
  * @param [in] temp The temperature value in 8.8 fixed point format.
  */
 void NimBLEEddystoneTLM::setTemp(int16_t temp) {
-    m_eddystoneData.temp = temp;
+    m_eddystoneData.temp = ENDIAN_CHANGE_U16(temp);
 } // setTemp
 
 /**
  * @brief Set the advertisement count.
  * @param [in] advCount The advertisement number.
  */
 void NimBLEEddystoneTLM::setCount(uint32_t advCount) {
-    m_eddystoneData.advCount = advCount;
+    m_eddystoneData.advCount = ENDIAN_CHANGE_U32(advCount);
 } // setCount
 
 /**
  * @brief Set the advertisement time.
  * @param [in] tmil The advertisement time in milliseconds.
  */
 void NimBLEEddystoneTLM::setTime(uint32_t tmil) {
-    m_eddystoneData.tmil = tmil;
+    m_eddystoneData.tmil = ENDIAN_CHANGE_U32(tmil);
 } // setTime
 
 #endif // CONFIG_BT_NIMBLE_ENABLED && MYNEWT_VAL(BLE_ROLE_BROADCASTER)

src/NimBLEEddystoneTLM.h

@@ -37,8 +37,8 @@ class NimBLEEddystoneTLM {
     struct BeaconData {
         uint8_t  frameType{EDDYSTONE_TLM_FRAME_TYPE};
         uint8_t  version{0};
-        uint16_t volt{3300};
-        uint16_t temp{23 * 256};
+        uint16_t volt{0xE40C}; // Big-endian (wire format) encoding of 3300 mV; getVolt() swaps back to host order.
+        uint16_t temp{0x0017}; // Big-endian (wire format) encoding of 23.0C (23 * 256); getTemp() swaps back to host order.
         uint32_t advCount{0};
         uint32_t tmil{0};
     } __attribute__((packed));