DDS and u-stepper calclations

ustep_calc.py

import bigfloat
import numpy

dds_clk=1.0e9
ftw_length = pow(2,48)
IF = 100e6/1024.0 # 97656.25

def ftw_dds(f_hz):
    return numpy.round(f_hz*ftw_length/dds_clk,0)

def hz_dds(ftw):
    return dds_clk*ftw/ftw_length

def y_out(ftw1, ftw2):
    """ fractional frequency of microstepper
        F_out / F_REF
    """
    with bigfloat.precision(200):
        F1term = bigfloat.BigFloat.exact(ftw1 )
        F2term = bigfloat.BigFloat.exact(ftw2/1024.0)
        Fsum = F1term+F2term
        y = 4.0*ftw_length* bigfloat.pow( 10.0*(Fsum), -1.0)-1
        return y

F1 = ftw_dds(400e6-4*IF)    # DDS1
F2 = ftw_dds(400e6)         # DDS2

y1 = y_out(F1,F2)
y2 = y_out(F1,F2+1)

print "uStep output fractional frequency y"
print "FTW1 = %d (constant)" % F1
print "FTW2\t\tdFTW2\ty"


for delta in [-5,-4,-3,-2,-1,0,1,2,3,4,5]:
    F2x = F2+delta-205
    y1 = y_out(F1,F2x) 
    print "%d\t%d\t%.3g" % ( F2x, delta, y1)

""" OUTPUT:
uStep output fractional frequency y
FTW1 = 112480039521485 (constant)
FTW2		dFTW2	y
112589990684052	-5	4.86e-17
112589990684053	-4	3.99e-17
112589990684054	-3	3.12e-17
112589990684055	-2	2.26e-17
112589990684056	-1	1.39e-17
112589990684057	0	5.2e-18
112589990684058	1	-3.47e-18
112589990684059	2	-1.21e-17
112589990684060	3	-2.08e-17
112589990684061	4	-2.95e-17
112589990684062	5	-3.82e-17

"""