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lockin-internal: rename, adapt

This commit is contained in:
Robert Jördens 2021-01-31 19:26:07 +01:00
parent 6e1444f070
commit 46a7d67027
2 changed files with 18 additions and 22 deletions
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0
src/bin/lockin.rs → src/bin/lockin-external.rs
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36
src/bin/lockin-internal-demo.rs → src/bin/lockin-internal.rs
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@ -74,8 +74,8 @@ const APP: () = {
// DAC0 always generates a fixed sinusoidal output. // DAC0 always generates a fixed sinusoidal output.
for (i, value) in DAC_SEQUENCE.iter().enumerate() { for (i, value) in DAC_SEQUENCE.iter().enumerate() {
// Full-scale gives a +/- 12V amplitude waveform. Scale it down to give +/- 100mV. // Full-scale gives a +/- 10V amplitude waveform. Scale it down to give +/- 1V.
let y = value * i16::MAX as f32 / 120.0; let y = value * (0.1 * i16::MAX as f32);
// Note(unsafe): The DAC_SEQUENCE values are guaranteed to be normalized. // Note(unsafe): The DAC_SEQUENCE values are guaranteed to be normalized.
let y = unsafe { y.to_int_unchecked::<i16>() }; let y = unsafe { y.to_int_unchecked::<i16>() };
@ -84,7 +84,8 @@ const APP: () = {
} }
let pll_phase = 0; let pll_phase = 0;
let pll_frequency = 1i32 << (32 - 3); // 1/8 of the sample rate // 1/8 of the sample rate: log2(DAC_SEQUENCE.len()) == 3
let pll_frequency = 1i32 << (32 - 3);
// Harmonic index of the LO: -1 to _de_modulate the fundamental // Harmonic index of the LO: -1 to _de_modulate the fundamental
let harmonic: i32 = -1; let harmonic: i32 = -1;
@ -92,28 +93,23 @@ const APP: () = {
// Demodulation LO phase offset // Demodulation LO phase offset
let phase_offset: i32 = (0.7495 * i32::MAX as f32) as i32; let phase_offset: i32 = (0.7495 * i32::MAX as f32) as i32;
let sample_frequency = (pll_frequency as i32).wrapping_mul(harmonic); let sample_frequency = (pll_frequency as i32).wrapping_mul(harmonic);
let mut sample_phase = phase_offset let sample_phase = phase_offset
.wrapping_add((pll_phase as i32).wrapping_mul(harmonic)); .wrapping_add((pll_phase as i32).wrapping_mul(harmonic));
let mut phase = 0i16; if let Some(output) = c.resources.lockin.feed(
adc_samples.iter().map(|&i|
for sample in adc_samples.iter() {
// Convert to signed, MSB align the ADC sample. // Convert to signed, MSB align the ADC sample.
let input = (*sample as i16 as i32) << 16; (i as i16 as i32) << 16),
sample_phase,
// Obtain demodulated, filtered IQ sample. sample_frequency,
let output = c.resources.lockin.update(input, sample_phase); ) {
// Convert from IQ to power and phase.
// Advance the sample phase. let _power = output.abs_sqr();
sample_phase = sample_phase.wrapping_add(sample_frequency); let phase = output.arg() >> 16;
// Convert from IQ to phase. Scale the phase so that it fits in the DAC range. We do
// this by shifting it down into the 16-bit range.
phase = (output.phase() >> 16) as i16;
}
for value in dac_samples[1].iter_mut() { for value in dac_samples[1].iter_mut() {
*value = phase as u16 ^ 0x8000 *value = phase as u16 ^ 0x8000;
}
} }
} }