src/rp2_common/hardware_clocks/scripts/vcocalc.py

#!/usr/bin/env python3

import argparse

parser = argparse.ArgumentParser(description="PLL parameter calculator")
parser.add_argument("--input", "-i", default=12, help="Input (reference) frequency. Default 12 MHz", type=float)
parser.add_argument("--ref-min", default=5, help="Override minimum reference frequency. Default 5 MHz", type=float)
parser.add_argument("--vco-max", default=1600, help="Override maximum VCO frequency. Default 1600 MHz", type=float)
parser.add_argument("--vco-min", default=750, help="Override minimum VCO frequency. Default 750 MHz", type=float)
parser.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")
parser.add_argument("output", help="Output frequency in MHz.", type=float)
args = parser.parse_args()

# Fixed hardware parameters
fbdiv_range = range(16, 320 + 1)
postdiv_range = range(1, 7 + 1)
ref_min = 5
refdiv_min = 1
refdiv_max = 63

refdiv_range = range(refdiv_min, max(refdiv_min, min(refdiv_max, int(args.input / args.ref_min))) + 1)

best = (0, 0, 0, 0, 0)
best_margin = args.output

for refdiv in refdiv_range:
	for fbdiv in (fbdiv_range if args.low_vco else reversed(fbdiv_range)):
		vco = args.input / refdiv * fbdiv
		if vco < args.vco_min or vco > args.vco_max:
			continue
		# pd1 is inner loop so that we prefer higher ratios of pd1:pd2
		for pd2 in postdiv_range:
			for pd1 in postdiv_range:
				out = vco / pd1 / pd2
				margin = abs(out - args.output)
				if margin < best_margin:
					best = (out, fbdiv, pd1, pd2, refdiv)
					best_margin = margin

print("Requested: {} MHz".format(args.output))
print("Achieved: {} MHz".format(best[0]))
print("REFDIV: {}".format(best[4]))
print("FBDIV: {} (VCO = {} MHz)".format(best[1], args.input / best[4] * best[1]))
print("PD1: {}".format(best[2]))
print("PD2: {}".format(best[3]))