# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1695412554 -7200
# Node ID 80a1c6ce717bab95609da453810ce3530c11b760
# Parent  e4d286a20f68dc483a201680f461ae7efc0dd72d
Added a tool to model various clock dividers.

diff -r e4d286a20f68 -r 80a1c6ce717b tools/dividers.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tools/dividers.py	Fri Sep 22 21:55:54 2023 +0200
@@ -0,0 +1,97 @@
+#!/usr/bin/env python2
+
+from math import ceil, floor
+import sys
+
+def method2(f, s):
+    r = f / s
+    scale = getscale(r)
+    return scale * r, scale
+
+def is_integer(x):
+    target = round(x) * 1000
+    #print x, target - 100, floor(x * 1000), target + 100
+    return target - 100 < floor(x * 1000) < target + 100
+
+def getscale(x):
+    scale = getscale_part(x)
+    if is_integer(scale):
+        return scale
+    return scale * getscale(scale)
+
+def getscale_part(x):
+    part = x - int(x)
+    if not part:
+        return 1
+    elif part > 0.5:
+        return 1 / (1 - part)
+    else:
+        return 1 / part
+
+def reduce(m, n, m_limit, n_limit):
+    while m > m_limit and n > n_limit and m > 1 and n > 1:
+        m /= 2
+        n /= 2
+    return m, n
+
+def show(s, m, n, f_label="f"):
+    print "m =", m
+    print "n =", n
+    print "%s' =" % f_label, s * m / n
+    print "%s' ~=" % f_label, s * round(m) / round(n)
+
+if len(sys.argv) < 4:
+    f, s = map(float, sys.argv[1:3])
+    m, n = method2(f, s)
+    m, n = reduce(m, n, 0x200, 0x100000)
+    show(s, m, n)
+
+else:
+    f, s, i_min, i_max = map(float, sys.argv[1:5])
+
+    # Constraints:
+    #
+    # i_min < s * m' / di < i_max
+    # i_min / s < m' / di < i_max / s
+    #
+    # f = s * m' / (di * do)
+    # f = (s * m' / di) / do
+    # f * do = s * m' / di
+    #
+    # i_min < f * do < i_max
+    # i_min / f < do < i_max / f
+    #
+    # f = s * m / n
+    #
+    # s * m' / (di * do) = s * m / n
+    # m' / (di * do) = m / n
+    # m' = (m / n) * (di * do)
+    # m' / di = (m / n) * do
+
+    do_min = ceil(i_min / f)
+    do_max = floor(i_max / f)
+
+    do = do_min
+
+    print do_min, "<= do <=", do_max
+
+    while do <= do_max:
+        do0 = int(do ** 0.5) 
+        do1 = int(do / do0)
+        if do0 * do1 == int(do):
+            i = do * f
+            m, n = method2(i, s)
+            m, n = reduce(m, n, 0x3f, 0x3f)
+            if m <= 0x3f and n <= 0x3f:
+                show(i, m, n, "i")
+                print "do =", do
+                print "do0 =", do0
+                print "do1 =", do1
+                print "f' =", s * m / (n * do)
+                print "f' ~=", s * round(m) / (round(n) * round(do))
+                break
+            else:
+                print "Ignored: m =", m, "n =", n, "do0 =", do0, "do1 =", do1
+        do += 1
+
+# vim: tabstop=4 expandtab shiftwidth=4