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