Reading BLE Characteristics in iOS

Question

Hi - I am trying to send a signed 16bit Integer from nRF52 to iOS. Using the following characteristic reader from Nordic in the nRF Toolbox on Github (here).

        static func readSInt16Value(ptr aPointer : inout UnsafeMutablePointer<UInt8>) -> Int16 {
    let anInt16Pointer = UnsafeMutablePointer<Int16>(OpaquePointer(aPointer))
    let val = CFSwapInt16LittleToHost(UnsafeMutablePointer<UInt16>(OpaquePointer(anInt16Pointer)).pointee)
    aPointer = aPointer.advanced(by: 2)
    return Int16(val)
   }

On the nRF52 side, packaging as follows:

'#define UINT16_TO_BSTREAM(p,n) {*(p)++ = (uint8_t)(n); *(p)++ = (uint8_t)((n)>>8);}

Any guidance on what I might be doing wrong would be greatly appreciated. Thanks!

dkwill · Accepted Answer

Finally found the solution. There is no "packaging" necessary on the nRF side. One of the main issues was not being able to handle a negative 16bit number. Anyway, here is the Swift code in the "didUpdateValueForCharacteristic function: 
 func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {

 if characteristic.uuid == CHAR1_UUID {
 
 let data = characteristic.value
 var pointer = UnsafeMutablePointer<UInt8>(mutating: (data! as NSData).bytes.bindMemory(to: UInt8.self, capacity: data!.count))
 
 let char1Data = NORCharacteristicReader.readUInt16Value(ptr: &pointer)
 let s: Int16 = Int16(bitPattern: UInt16(char1Data))
}
}
 
 The only real change from the Nordic Toolbox code was to add the last line for the bitPattern. Anyway, hope it might help someone else with the same issue. Surprising how long it took for only one line of code!

Reading BLE Characteristics in iOS

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