Confused why solutions do not satisfy constraints...

[opsound]

from __future__ import print_function
from Numberjack import *

# find PLLN, PLLM, PLLP, PLLQ
# constraints
# f_VCO = f_PLL_input * PLLN / PLLM ... 100 MHz <= f_VCO <= 432 MHz ... 50 <= PLLN <= 432 ... 2 <= PLLM <= 63
# f_PLL = f_VCO / PLLP ... PLLP = 2,4,6,8 .. f_PLL = 180 MHz
# f_USB = f_VCO / PLLQ ... 2 <= PLLQ <= 15 ... f_USB = 48 MHz

f_input = 8
f_pll = 180
f_usb = 48

n = Variable(50,432)
m = Variable(2,63)
p = Variable([2,4,6,8])
q = Variable(2,15)
f_vco = Variable(100,432)

model = Model(
    f_vco == f_input * n / m,
    f_pll == f_vco / p,
    f_usb == f_vco / q,
)

solver = model.load("Mistral")
solver.solve()
for x in solver.solutions():
    print("n = {}, m = {}, p = {}, q = {}, f_vco = {}".format(n.get_value(), m.get_value(), p.get_value(), q.get_value(), f_vco.get_value()))

Output

n = 144, m = 3, p = 2, q = 8, f_vco = 384
n = 192, m = 4, p = 2, q = 8, f_vco = 384
n = 240, m = 5, p = 2, q = 8, f_vco = 384
n = 288, m = 6, p = 2, q = 8, f_vco = 384
n = 336, m = 7, p = 2, q = 8, f_vco = 384
n = 384, m = 8, p = 2, q = 8, f_vco = 384
n = 432, m = 9, p = 2, q = 8, f_vco = 384
...

I don't understand why the solutions don't satisfy the constraints:

f_vco / p = f_pll
384 / 2 = 192 ? (not 180)

Is there some mistake in my problem formulation?

[opsound]

I relaxed the f_pll constraint by changing it to

    180 >= f_vco / p,
    150 <= f_vco / p,

and it looks like there isn't a solution that can satisfy both f_usb == 48 and f_pll == 180.