Initial Galileo receiver and SignalSim integration

2026-07-30 23:26:03 +03:00
commit 2a6ccfc23d
153 changed files with 8080 additions and 0 deletions
@@ -0,0 +1,45 @@
+# Fixed-point plan
+
+The fixed framework represents signed two's-complement integers with declared
+total/fractional widths. Every quantizer selects saturation or wrap and nearest,
+truncate, or convergent ties-to-even rounding. Quantizers count overflow and
+accumulate RMS/peak quantization error.
+
+Proposed starting points (not final widths):
+
+| Stage | Width | Fraction | Policy |
+|---|---:|---:|---|
+| input sample | 8 | 7 | saturate |
+| sine/cosine | 16 | 15 | saturate |
+| mixer output | 18 | 15 | saturate |
+| FFT input | 18 | 15 | saturate |
+| FFT twiddle | 16 | 15 | convergent |
+| FFT stage | 20 | 15 | configured scaling |
+| correlation product | 36 | 30 | full precision then requantize |
+| IFFT output | 28 | 15 | saturate |
+| coherent accumulator | 40 | 15 | saturate |
+| noncoherent accumulator | unsigned 56 | 20 | saturate |
+| carrier phase | unsigned 32 | 0 | natural wrap |
+| code phase | unsigned 48 | 32 | natural wrap |
+| loop state | 32 | 20 | saturate |
+| FCW | signed 32 | 0 | wrap in phase accumulator |
+| discriminator | 24 | 18 | saturate |
+
+`FixedNco` and `FixedCorrelator` are integer bit-true models. Fixed PCPS models
+declared quantization at input, normalized FFT output, pointwise product, IFFT
+output/power, and accumulation. Exact butterfly-level identity depends on the
+chosen streaming FFT IP scaling schedule and is explicitly unresolved until an
+RTL FFT architecture is selected.
+
+`FixedRadix2Fft` supplies a fully stage-quantized power-of-two oracle with
+quantized twiddles, convergent butterfly rounding, saturation counters, and one
+bit of scaling per stage. It is used for standalone RTL FFT vectors. The
+runtime PCPS boundary model remains able to use arbitrary transform lengths;
+matching a vendor FFT at those lengths requires configuring that core's exact
+schedule.
+
+The sweep utility varies input/FFT widths and reports mean absolute/relative,
+RMS, peak error, acquisition decision, Doppler bin, code phase, and overflows.
+Tracking qualification additionally compares convergence, steady-state jitter,
+and loss-of-lock decisions; these metrics must become release gates once loop
+state formats are frozen.