1#!/usr/bin/env python3
2
3import argparse
4
5parser = argparse.ArgumentParser(description="PLL parameter calculator")
6parser.add_argument("--input", "-i", default=12, help="Input (reference) frequency. Default 12 MHz", type=float)
7parser.add_argument("--ref-min", default=5, help="Override minimum reference frequency. Default 5 MHz", type=float)
8parser.add_argument("--vco-max", default=1600, help="Override maximum VCO frequency. Default 1600 MHz", type=float)
9parser.add_argument("--vco-min", default=750, help="Override minimum VCO frequency. Default 750 MHz", type=float)
10parser.add_argument("--low-vco", "-l", action="store_true", help="Use a lower VCO frequency when possible. This reduces power consumption, at the cost of increased jitter")
11parser.add_argument("output", help="Output frequency in MHz.", type=float)
12args = parser.parse_args()
13
14# Fixed hardware parameters
15fbdiv_range = range(16, 320 + 1)
16postdiv_range = range(1, 7 + 1)
17ref_min = 5
18refdiv_min = 1
19refdiv_max = 63
20
21refdiv_range = range(refdiv_min, max(refdiv_min, min(refdiv_max, int(args.input / args.ref_min))) + 1)
22
23best = (0, 0, 0, 0, 0)
24best_margin = args.output
25
26for refdiv in refdiv_range:
27	for fbdiv in (fbdiv_range if args.low_vco else reversed(fbdiv_range)):
28		vco = args.input / refdiv * fbdiv
29		if vco < args.vco_min or vco > args.vco_max:
30			continue
31		# pd1 is inner loop so that we prefer higher ratios of pd1:pd2
32		for pd2 in postdiv_range:
33			for pd1 in postdiv_range:
34				out = vco / pd1 / pd2
35				margin = abs(out - args.output)
36				if margin < best_margin:
37					best = (out, fbdiv, pd1, pd2, refdiv)
38					best_margin = margin
39
40print("Requested: {} MHz".format(args.output))
41print("Achieved: {} MHz".format(best[0]))
42print("REFDIV: {}".format(best[4]))
43print("FBDIV: {} (VCO = {} MHz)".format(best[1], args.input / best[4] * best[1]))
44print("PD1: {}".format(best[2]))
45print("PD2: {}".format(best[3]))
46