I obtain magnetometer trim register as get NSData() that looks as follows:
<00001a1a 4f56f202 00000000 1dfd421b>
s8 dig_x1;/**< trim x1 data */
s8 dig_y1;/**< trim y1 data */
s8 dig_x2;/**< trim x2 data */
s8 dig_y2;/**< trim y2 data */
u16 dig_z1;/**< trim z1 data */
s16 dig_z2;/**< trim z2 data */
s16 dig_z3;/**< trim z3 data */
s16 dig_z4;/**< trim z4 data */
u8 dig_xy1;/**< trim xy1 data */
s8 dig_xy2;/**< trim xy2 data */
u16 dig_xyz1;/**< trim xyz1 data *
You can convert data.bytes + offset
to a pointer of the
appropriate type and then dereference the pointer:
let dig_x1 = UnsafePointer<Int8>(data.bytes).memory
let dig_y1 = UnsafePointer<Int8>(data.bytes + 1).memory
// ...
let dig_z1 = UnsafePointer<UInt16>(data.bytes + 4).memory
let dig_z2 = UnsafePointer<Int16>(data.bytes + 6).memory
// ...
The data is in little-endian byte order, which is also what all current iOS platforms use. To be on the safe side, convert the data to host byte order explicitly:
let dig_z1 = UInt16(littleEndian: UnsafePointer(data.bytes + 4).memory)
let dig_z2 = Int16(littleEndian: UnsafePointer(data.bytes + 6).memory)
// ...
An alternative is to define a C structure in the bridging header file
struct MagnetometerData {
int8_t dig_x1;
int8_t dig_y1;
int8_t dig_x2;
int8_t dig_y2;
uint16_t dig_z1;
int16_t dig_z2;
int16_t dig_z3;
int16_t dig_z4;
uint8_t dig_xy1;
int8_t dig_xy2;
uint16_t dig_xyz1;
} ;
and extract the data in one step:
var mdata = MagnetometerData()
data.getBytes(&mdata, length: sizeofValue(mdata))
This works (if there is no padding between the struct members) because Swift preserves the layout of structures imported from C.