Implement Galileo E1B I/NAV navigation decoding

2026-07-31 00:15:34 +03:00
parent 2a6ccfc23d
commit 814a788b36
104 changed files with 6351 additions and 10 deletions
@@ -0,0 +1,57 @@
+# Navigation hardware/software partition
+
+The measured partition keeps sample-rate work in the tracking IP and performs
+I/NAV decoding in software. No result in this milestone justifies placing a
+soft-decision Viterbi decoder or navigation database in RTL.
+
+## Tracking-IP output contract
+
+One record is emitted for every 4 ms E1B primary-code epoch:
+
+| Field | Proposed representation | Meaning |
+| --- | --- | --- |
+| PRN/channel | unsigned integer | Logical satellite and component |
+| start/end timestamp | 64-bit sample counters | Continuous receiver time association |
+| Prompt I/Q | signed fixed-point accumulators | Unreduced coherent evidence |
+| carrier phase/frequency | NCO state/measurement words | Reprocessing and phase diagnostics |
+| code phase | unsigned fixed-point chips | Code-time association |
+| C/N0 | fixed-point dB-Hz or invalid | Monitoring only |
+| carrier/code lock | bits | Decoder validity gate |
+| cycle slip/discontinuity | bits | Immediate symbol/page synchronizer reset |
+| valid | bit | Transaction validity |
+
+The interface should use an AXI-Stream-like `valid/ready` transaction. A FIFO
+must absorb software service latency; backpressure cannot be allowed to stop the
+sample-rate tracking datapath. At 250 records/s/channel, even 36 active E1B
+channels produce only 9000 records/s, so a memory-mapped DMA ring is sufficient.
+
+## Software decoder
+
+Software retains floating `numpy.float64` prompt/soft values in the reference
+model and performs:
+
+```text
+prompt axis and symbol synchronization
+  -> page synchronization and polarity resolution
+  -> 30x8 deinterleaving
+  -> soft Viterbi decode
+  -> vertical-page assembly and CRC-24Q
+  -> typed word parsing
+  -> atomic IODnav ephemeris assembly
+  -> GST/clock/health navigation database
+```
+
+This split keeps policy-rich, low-rate state machines inspectable and updateable.
+The saved `prompt_epochs.npz` files are the exact boundary between future RTL
+tracking and the software decoder. HDL verification shall replay the same RF
+vector, compare each tracking epoch with the bit-true model, then feed the RTL
+prompt records into this decoder without SignalSim truth.
+
+## Conditions that could justify later hardware offload
+
+Only measured CPU load, power, or startup-latency failure should trigger an
+offload study. Plausible granular offloads are symbol accumulate-and-dump,
+deinterleaver address generation, or a shared Viterbi accelerator. CRC, word
+parsing, ephemeris consistency, time rollover handling, and the navigation store
+remain better software candidates because their throughput is negligible and
+their standards/policy behavior is state-rich.