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"""
This is an auxiliary script that is used to compute valid PLL values to set
the CPU frequency to a given value. The algorithm here appears as C code
for the machine.freq() function.
"""
def close_int(x):
return abs(x - round(x)) < 0.01
# original version that requires N/M to be an integer (for simplicity)
def compute_pll(hse, sys):
for P in (2, 4, 6, 8): # allowed values of P
Q = sys * P / 48
NbyM = sys * P / hse
# N/M and Q must be integers
if not (close_int(NbyM) and close_int(Q)):
continue
# VCO_OUT must be between 192MHz and 432MHz
if not (192 <= hse * NbyM <= 432):
continue
# compute M
M = int(192 // NbyM)
while hse > 2 * M or NbyM * M < 192:
M += 1
# VCO_IN must be between 1MHz and 2MHz (2MHz recommended)
if not (M <= hse):
continue
# compute N
N = NbyM * M
# N and Q are restricted
if not (192 <= N <= 432 and 2 <= Q <= 15):
continue
# found valid values
assert NbyM == N // M
return (M, N, P, Q)
# no valid values found
return None
# improved version that doesn't require N/M to be an integer
def compute_pll2(hse, sys):
for P in (2, 4, 6, 8): # allowed values of P
Q = sys * P / 48
# Q must be an integer in a set range
if not (close_int(Q) and 2 <= Q <= 15):
continue
NbyM = sys * P / hse
# VCO_OUT must be between 192MHz and 432MHz
if not (192 <= hse * NbyM <= 432):
continue
# compute M
M = 192 // NbyM # starting value
while hse > 2 * M or NbyM * M < 192 or not close_int(NbyM * M):
M += 1
# VCO_IN must be between 1MHz and 2MHz (2MHz recommended)
if not (M <= hse):
continue
# compute N
N = NbyM * M
# N must be an integer
if not close_int(N):
continue
# N is restricted
if not (192 <= N <= 432):
continue
# found valid values
return (M, N, P, Q)
# no valid values found
return None
def verify_and_print_pll(hse, sys, pll):
M, N, P, Q = pll
# compute derived quantities
vco_in = hse / M
vco_out = hse * N / M
pllck = hse / M * N / P
pll48ck = hse / M * N / Q
# verify ints
assert close_int(M)
assert close_int(N)
assert close_int(P)
assert close_int(Q)
# verify range
assert 2 <= M <= 63
assert 192 <= N <= 432
assert P in (2, 4, 6, 8)
assert 2 <= Q <= 15
assert 1 <= vco_in <= 2
assert 192 <= vco_out <= 432
# print out values
print(out_format % (sys, M, N, P, Q, vco_in, vco_out, pllck, pll48ck))
def main():
global out_format
import sys
if len(sys.argv) != 2:
print("usage: pllvalues.py <hse in MHz>")
sys.exit(1)
hse_value = int(sys.argv[1])
print("HSE =", hse_value, "MHz")
print("sys : M N P Q : VCO_IN VCO_OUT PLLCK PLL48CK")
out_format = "%3u : %2u %.1f %.2f %.2f : %5.2f %6.2f %6.2f %6.2f"
n_valid = 0
for sysclk in range(1, 217):
pll = compute_pll2(hse_value, sysclk)
if pll is not None:
n_valid += 1
verify_and_print_pll(hse_value, sysclk, pll)
print("found %u valid configurations" % n_valid)
if __name__ == "__main__":
main()
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