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Fractional divider calculator
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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 | |
# See also: https://gist.github.com/endolith/114336 | |
__author__ = "Andy Shevchenko" | |
__license__ = "GPL v2" | |
PROG = os.path.basename(sys.argv[0]) | |
BAUDRATES = [ | |
# Group 0 | |
110, | |
134, | |
# Group 1 | |
50, | |
75, | |
150, | |
200, | |
300, | |
600, | |
1200, | |
1800, | |
2400, | |
4800, | |
9600, | |
19200, | |
38400, | |
57600, | |
115200, | |
230400, | |
460800, | |
921600, | |
1843200, | |
# Group 2 | |
576000, | |
1152000, | |
# Group 3 | |
500000, | |
1000000, | |
1500000, | |
2000000, | |
2500000, | |
3000000, | |
3500000, | |
4000000, | |
] | |
XTAL = 38400000 | |
PS = 16 | |
RW = 14 | |
ALGO = 1 | |
# | |
# Fref = XTAL * m / n | |
# uartclk = Fuart * 16 / ps | |
# baud = uartclk / (ps * DLAB) | |
# | |
def go(xtal, baud, rw, ps, algo): | |
# | |
# Iterative | |
# | |
# while True: | |
# fuart = baud * ps | |
# if fuart < xtal: | |
# break | |
# ps -= 1 | |
# if (ps == 1): | |
# break; | |
# i = 1 | |
# while True: | |
# if (xtal - fuart * i) < fuart: | |
# break | |
# i += 1 | |
# fuart *= i | |
# | |
# Fast | |
# | |
fuart = baud * ps | |
if xtal < fuart: | |
if xtal >= baud: | |
ps = xtal / baud | |
else: | |
ps = 1 | |
fuart = baud * ps | |
elif algo & 1 == 0: | |
# in C we use fls() | |
scale = int(math.ceil(math.log(xtal / fuart, 2))) | |
if scale > rw: | |
fuart <<= scale - rw | |
else: | |
fuart <<= int(math.log(xtal / fuart, 2)) | |
# | |
# Fast: consider to replace while-loop by fls(n >> rw) | |
# | |
# div = fractions.gcd(xtal, fuart) | |
# n = xtal / div | |
# while n > (2 ** rw - 1): | |
# div <<= 1 | |
# n >>= 1 | |
# m = fuart / div | |
# return m, n, ps, fuart * 16 / ps | |
# | |
# Precise: rational best approximation | |
# | |
f = fractions.Fraction(fuart, xtal).limit_denominator(2 ** rw - 1) | |
return f.numerator, f.denominator, ps, fuart * 16 / ps | |
def usage(): | |
sys.stdout.write("Usage %s [XTAL [PS [RW [ALGO]]]]\n" % PROG) | |
def toint(value): | |
try: | |
return int(value) | |
except ValueError: | |
usage() | |
raise SystemExit("Invalid argument") | |
def main(argv): | |
if len(argv) > 1: | |
xtal = toint(argv[1]) | |
else: | |
xtal = XTAL | |
if len(argv) > 2: | |
presc = toint(argv[2]) | |
else: | |
presc = PS | |
if len(argv) > 3: | |
rw = toint(argv[3]) | |
else: | |
rw = RW | |
if len(argv) > 4: | |
algo = toint(argv[4]) | |
else: | |
algo = ALGO | |
bauds = dict() | |
for b in sorted(BAUDRATES): | |
m, n, ps, uartclk = go(xtal, b, rw, presc, algo) | |
if (m, n, ps, uartclk) not in bauds: | |
bauds[(m, n, ps, uartclk)] = list() | |
bauds[(m, n, ps, uartclk)].append(b) | |
for m, n, ps, uartclk in sorted(bauds, key=operator.itemgetter(2, 1, 0)): | |
fref = xtal * m / n | |
fuart = uartclk * ps / 16 | |
dev = (abs(1.0 - fref * 1.0 / fuart) * 100) | |
brs = ["%d(%d)" % (b, uartclk / 16 / b) for b in bauds[(m, n, ps, uartclk)]] | |
dm = (fref - fuart) and '*' or ' ' | |
#print "%-8d %-8d %-2d %-10d %-10d %s%.2f %s" % (m, n, ps, fref, uartclk, dm, dev, ','.join(brs)) | |
print "%-8d %-8d %-2d %-10d %-10d %s" % (m, n, ps, fref, uartclk, ','.join(brs)) | |
if __name__ == "__main__": | |
sys.exit(main(sys.argv)) |
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