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lockin: de-nest processing flow

This commit is contained in:
Robert Jördens 2021-02-01 18:14:09 +01:00
parent b6e22b576b
commit f9b5d29450
2 changed files with 43 additions and 33 deletions
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40
src/bin/lockin-external.rs
View File

@ -119,21 +119,23 @@ const APP: () = {
let (pll_phase, pll_frequency) = c.resources.pll.update(
c.resources.timestamper.latest_timestamp().map(|t| t as i32),
23, // relative PLL frequency bandwidth: 2**-23, TODO: expose
22, // relative PLL phase bandwidth: 2**-22, TODO: expose
22, // frequency settling time (log2 counter cycles), TODO: expose
22, // phase settling time, TODO: expose
);
// Harmonic index of the LO: -1 to _de_modulate the fundamental (complex conjugate)
let harmonic: i32 = -1;
let harmonic: i32 = -1; // TODO: expose
// Demodulation LO phase offset
let phase_offset: i32 = 0;
let sample_frequency = ((pll_frequency >> SAMPLE_BUFFER_SIZE_LOG2)
as i32) // TODO: maybe rounding bias
let phase_offset: i32 = 0; // TODO: expose
let sample_frequency = ((pll_frequency
// .wrapping_add(1 << SAMPLE_BUFFER_SIZE_LOG2 - 1) // half-up rounding bias
>> SAMPLE_BUFFER_SIZE_LOG2) as i32)
.wrapping_mul(harmonic);
let sample_phase =
phase_offset.wrapping_add(pll_phase.wrapping_mul(harmonic));
if let Some(output) = adc_samples[0]
let output = adc_samples[0]
.iter()
.zip(Accu::new(sample_phase, sample_frequency))
// Convert to signed, MSB align the ADC sample.
@ -141,16 +143,25 @@ const APP: () = {
lockin.update((sample as i16 as i32) << 16, phase)
})
.last()
{
.unwrap();
// convert i/q to power/phase,
let power_phase = true; // TODO: expose
let mut output = if power_phase {
// Convert from IQ to power and phase.
let mut power = output.abs_sqr() as _;
let mut phase = output.arg() as _;
[output.abs_sqr() as _, output.arg() as _]
} else {
[output.0 as _, output.1 as _]
};
// Filter power and phase through IIR filters.
// Note: Normalization to be done in filters. Phase will wrap happily.
for j in 0..iir_state[0].len() {
power = iir_ch[0][j].update(&mut iir_state[0][j], power);
phase = iir_ch[1][j].update(&mut iir_state[1][j], phase);
for k in 0..output.len() {
output[k] =
iir_ch[k][j].update(&mut iir_state[k][j], output[k]);
}
}
// Note(unsafe): range clipping to i16 is ensured by IIR filters above.
@ -158,10 +169,9 @@ const APP: () = {
for i in 0..dac_samples[0].len() {
unsafe {
dac_samples[0][i] =
power.to_int_unchecked::<i16>() as u16 ^ 0x8000;
output[0].to_int_unchecked::<i16>() as u16 ^ 0x8000;
dac_samples[1][i] =
phase.to_int_unchecked::<i16>() as u16 ^ 0x8000;
}
output[1].to_int_unchecked::<i16>() as u16 ^ 0x8000;
}
}
}

6
src/bin/lockin-internal.rs
View File

@ -95,7 +95,7 @@ const APP: () = {
let sample_phase = phase_offset
.wrapping_add((pll_phase as i32).wrapping_mul(harmonic));
if let Some(output) = adc_samples
let output = adc_samples
.iter()
// Zip in the LO phase.
.zip(Accu::new(sample_phase, sample_frequency))
@ -105,7 +105,8 @@ const APP: () = {
})
// Decimate
.last()
{
.unwrap();
// Convert from IQ to power and phase.
let _power = output.abs_sqr();
let phase = output.arg() >> 16;
@ -114,7 +115,6 @@ const APP: () = {
*value = phase as u16 ^ 0x8000;
}
}
}
#[idle(resources=[afes])]
fn idle(_: idle::Context) -> ! {