How to display float number in MCP App?

Question

Hi there! 
 I want to send a float from nRF51822 to MCP App. I use this code: 
 float m_temperature = 26.3f;
uint8_array_t temperature_data_array;
temperature_data_array.p_data = (uint8_t*)(&m_temperature);
temperature_data_array.size = sizeof(m_temperature);

ble_advdata_service_data_t service_data[1] = {{APP_TEMPERATURE_UUID, temperature_data_array},
 };

sradvdata.p_service_data_array = service_data; // Pointer to Service Data structure.
sradvdata.service_data_count = 1;
ble_advdata_set(&advdata, &sradvdata);
 
 But in MCP App, It display "-Infinity" error when I select data format Float32. 
 Thanks.

MartinBL · Accepted Answer

Hi 
 I believe this is an issue regarding endianness and floating point formats. Bluetooth and our SDKs are using the IEEE-11073 format while the app is using IEEE-754 format . Here is an overveiw of what the IEEE-11073 is all about. 
 IEEE-11073 standard (from PDF): 
 
 IEEE-754 standard: 
 
 The endianness issue is discussed here . 
 It seems like there is an easy fix on the Android side (I have not tried it), but it is not implemented in the app. If you look in the ble_app_hts example in the SDK you can see how the temperature value's exponent and mantissa is stored in a struct: 
 typedef struct
{
 int8_t exponent; /**< Base 10 exponent */
 int32_t mantissa; /**< Mantissa, should be using only 24 bits */
} ieee_float32_t;
 
 Before transmission the exponent and mantissa are encoded into a four bytes long buffer and the bytes are reversed (it happens in hts_measurement_encode() in the SDK example). Finally the float is treated as a 11073 format float on the other side.

How to display float number in MCP App?

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