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vendor.GowinPlatform: account for rouding error in frequency calculation.

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This commit is contained in:
Catherine 2023-09-02 21:34:04 +00:00
parent 47851c2328
commit d27681b157
1 changed files with 5 additions and 2 deletions
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7
amaranth/vendor/_gowin.py
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@ -164,7 +164,10 @@ class GowinPlatform(TemplatedPlatform):
div_range = range(2, 130, 2)
div_frac = Fraction(self._osc_base_freq, self.osc_frequency)
if div_frac.denominator != 1 or div_frac not in div_range:
# Check that the requested frequency is within 50 ppm. This takes care of small mismatches
# arising due to rounding. The tolerance of a typical crystal oscillator is 50 ppm.
if (abs(round(div_frac) - div_frac) > Fraction(50, 1_000_000) or
int(div_frac) not in div_range):
achievable = (
min((frac for frac in div_range if frac > div_frac), default=None),
max((frac for frac in div_range if frac < div_frac), default=None)
@ -178,7 +181,7 @@ class GowinPlatform(TemplatedPlatform):
f"achievable frequencies are " +
", ".join(str(self._osc_base_freq // frac) for frac in achievable if frac))
return div_frac.numerator
return int(div_frac)
# Common templates