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fastino: expand docs

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This commit is contained in:
Robert Jördens 2021-10-28 15:19:48 +00:00
parent 1ff474893d
commit 5a5b0cc7c0
1 changed files with 25 additions and 11 deletions
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36
artiq/coredevice/fastino.py
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@ -200,7 +200,7 @@ class Fastino:
@kernel
def stage_cic_mu(self, rate_mantissa, rate_exponent, gain_exponent):
"""Stage machine unit interpolator configuration.
"""Stage machine unit CIC interpolator configuration.
"""
if rate_mantissa < 0 or rate_mantissa >= 1 << 6:
raise ValueError("rate_mantissa out of bounds")
@ -215,15 +215,18 @@ class Fastino:
def stage_cic(self, rate) -> TInt32:
"""Compute and stage interpolator configuration.
Approximates rate using 6+4 bit floating point representation,
approximates optimal interpolation gain compensation exponent to avoid
clipping. Gains for rates that are powers of two are accurately
compensated. Other rates lead to overall less than unity gain.
This method approximates the desired interpolation rate using a 10 bit
floating point representation (6 bit mantissa, 4 bit exponent) and
then determines an optimal interpolation gain compensation exponent
to avoid clipping. Gains for rates that are powers of two are accurately
compensated. Other rates lead to overall less than unity gain (but more
than 0.5 gain).
Returns the actual interpolation rate.
The actual overall interpolation gain including gain compensation is
The overall gain including gain compensation is
`actual_rate**order/2**ceil(log2(actual_rate**order))`
where `order = 3`.
Returns the actual interpolation rate.
"""
if rate <= 0 or rate > 1 << 16:
raise ValueError("rate out of bounds")
@ -248,10 +251,21 @@ class Fastino:
def apply_cic(self, channel_mask):
"""Apply the staged interpolator configuration on the specified channels.
Channels using non-unity interpolation rate and variable data should have
continous DAC updates enabled (see :meth:`set_continuous`).
Each Fastino channel includes a fourth order (cubic) CIC interpolator with
variable rate change and variable output gain compensation (see
:meth:`stage_cic`).
This resets and settles the interpolators. There will be no output
updates for the next `order = 3` input samples.
Channels using non-unity interpolation rate should have
continous DAC updates enabled (see :meth:`set_continuous`) unless
their output is supposed to be constant.
This method resets and settles the affected interpolators. There will be
no output updates for the next `order = 3` input samples.
Affected channels will only accept one input sample per input sample
period. This method synchronizes the input sample period to the current
frame on the affected channels.
If application of new interpolator settings results in a change of the
overall gain, there will be a corresponding output step.
"""
self.write(0x27, channel_mask)