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Fractional divider for LPSS PWM
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#!/usr/bin/python -tt | |
# -*- coding: UTF-8 -*- | |
# vim: ts=4 sw=4 et ai si | |
import sys | |
import os | |
import operator | |
import math | |
import fractions | |
__author__ = "Andy Shevchenko" | |
__license__ = "GPL v2" | |
PROG = os.path.basename(sys.argv[0]) | |
FSYS = 19200000 | |
# Test date (pertiod, duty cycle) | |
TABLE = [ | |
[100, 50], | |
[300, 250], | |
[1000, 250], | |
[50000, 10000], | |
[100000, 75000], | |
[300000, 50000], | |
[500000, 250000], | |
[20000000, 10000000], | |
[1, 1], | |
[53, 1], | |
[104, 1], | |
[256, 1], | |
[FSYS - 2, 1], | |
[FSYS - 1, FSYS - 2], | |
[FSYS, 1], | |
[FSYS, FSYS - 1], | |
] | |
def go(fref, period, duty): | |
freq = 10**9 / period | |
# | |
# The equation is: | |
# base_unit = round(base_unit_range * freq / c) | |
# | |
bur = 2**22 | |
freq *= bur; | |
bu = freq / fref; | |
if duty > 0: | |
d = duty | |
else: | |
d = 1 | |
otd = 255 * d | |
otd /= period | |
otd = 255 - otd | |
bul = bu & (bur - 1) | |
r = (bul << 8) + otd | |
pf = fref * bul * 1.0 / bur | |
dp = otd * 100.0 / 256 | |
print "%d %d(%d): div: %d bu: %#x(%#x) -> %#x out freq: %.1f duty: %.2f(%.2f)%%" % ( | |
period, duty, d, otd, bu, bul, r, pf, dp, duty * 100.0 / period | |
) | |
def usage(): | |
sys.stdout.write("Usage %s [period [duty]]\n" % PROG) | |
def toint(value): | |
try: | |
return int(value) | |
except ValueError: | |
usage() | |
raise SystemExit("Invalid argument") | |
def main(argv): | |
fref = FSYS | |
if len(argv) > 1: | |
period = toint(argv[1]) | |
if len(argv) > 2: | |
duty = toint(argv[2]) | |
else: | |
duty = period / 2 | |
go(fref, period, duty) | |
else: | |
for item in TABLE: | |
go(fref, operator.itemgetter(0)(item), operator.itemgetter(1)(item)) | |
if __name__ == "__main__": | |
sys.exit(main(sys.argv)) |
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