Embedded Software and Motor Control Libraries for PXR40xx

4.35.1 Declaration
tFrac16 GFLIB_AtanYX_F16(tFrac16 f16InY, tFrac16 f16InX);
4.35.2 Arguments
Table 4-45. GFLIB_AtanYX_F16 arguments
Type Name Direction Description
tFrac16 f16InY input The ordinate of the input vector (y coordinate).
tFrac16 f16InX input The abscissa of the input vector (x coordinate).
4.35.3 Return
The function returns the angle between the positive x-axis of a plane and the direction of
the vector given by the x and y coordinates provided as parameters.
4.35.4 Description
The function returns the angle between the positive x-axis of a plane and the direction of
the vector given by the x and y coordinates provided as parameters. The first parameter,
f16InY, is the ordinate (the y coordinate) and the second one, f16InX, is the abscissa (the
x coordinate).
Both the input parameters are assumed to be in the fractional range of [-1, 1). The
computed angle is limited by the fractional range of [-1, 1), which corresponds to the real
range of [- π, π). The counter-clockwise direction is assumed to be positive and thus a
positive angle will be computed if the provided ordinate (f16InY) is positive. Similarly, a
negative angle will be computed for the negative ordinate.
The calculations are performed in a few steps.
Chapter 4 API References
In the first step, the angle is positioned within the correct half-quarter of the
circumference of a circle by dividing the angle into two parts: the integral multiple of 45
deg (half-quarter) and the remaining offset within the 45 deg range. Simple geometric
properties of the Cartesian coordinate system are used to calculate the coordinates of the
vector with the calculated angle offset.
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
Freescale Semiconductor, Inc. 249