forked from M-Labs/artiq
fastino: expand docs
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@ -200,7 +200,7 @@ class Fastino:
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@kernel
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def stage_cic_mu(self, rate_mantissa, rate_exponent, gain_exponent):
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"""Stage machine unit interpolator configuration.
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"""Stage machine unit CIC interpolator configuration.
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"""
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if rate_mantissa < 0 or rate_mantissa >= 1 << 6:
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raise ValueError("rate_mantissa out of bounds")
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@ -215,15 +215,18 @@ class Fastino:
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def stage_cic(self, rate) -> TInt32:
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"""Compute and stage interpolator configuration.
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Approximates rate using 6+4 bit floating point representation,
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approximates optimal interpolation gain compensation exponent to avoid
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clipping. Gains for rates that are powers of two are accurately
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compensated. Other rates lead to overall less than unity gain.
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This method approximates the desired interpolation rate using a 10 bit
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floating point representation (6 bit mantissa, 4 bit exponent) and
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then determines an optimal interpolation gain compensation exponent
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to avoid clipping. Gains for rates that are powers of two are accurately
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compensated. Other rates lead to overall less than unity gain (but more
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than 0.5 gain).
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Returns the actual interpolation rate.
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The actual overall interpolation gain including gain compensation is
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The overall gain including gain compensation is
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`actual_rate**order/2**ceil(log2(actual_rate**order))`
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where `order = 3`.
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Returns the actual interpolation rate.
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"""
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if rate <= 0 or rate > 1 << 16:
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raise ValueError("rate out of bounds")
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@ -248,10 +251,21 @@ class Fastino:
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def apply_cic(self, channel_mask):
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"""Apply the staged interpolator configuration on the specified channels.
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Channels using non-unity interpolation rate and variable data should have
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continous DAC updates enabled (see :meth:`set_continuous`).
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Each Fastino channel includes a fourth order (cubic) CIC interpolator with
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variable rate change and variable output gain compensation (see
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:meth:`stage_cic`).
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This resets and settles the interpolators. There will be no output
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updates for the next `order = 3` input samples.
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Channels using non-unity interpolation rate should have
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continous DAC updates enabled (see :meth:`set_continuous`) unless
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their output is supposed to be constant.
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This method resets and settles the affected interpolators. There will be
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no output updates for the next `order = 3` input samples.
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Affected channels will only accept one input sample per input sample
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period. This method synchronizes the input sample period to the current
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frame on the affected channels.
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If application of new interpolator settings results in a change of the
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overall gain, there will be a corresponding output step.
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"""
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self.write(0x27, channel_mask)
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