LibreVNA/Software
Roger Henderson 1ea012aa57 implement FPGA-based CDS to avoid BRAM overflow
Move CDS phase computation from per-point config storage to FPGA logic.
The FPGA now computes the 180° phase shift internally (M/2) and loops
twice per point when CDS is enabled. This keeps config memory at 96 bits
instead of 112, avoiding BRAM overflow on the Spartan 6.

FPGA changes:
- Add CDS_ENABLED input to Sweep module (controlled via SPI register 6)
- Compute source_phase = M/2 for 180° shift when cds_phase=1
- State machine loops through all stages twice per point when CDS enabled
- RESULT_INDEX now includes cds_phase bit: stage[2:0] & point[11:0] & cds_phase

Firmware changes:
- Add FPGA::SetCDSEnabled() to control CDS via register 6 bit 11
- Update SamplingResult to include cdsPhase field (1 bit)
- Simplify VNA.cpp: FPGA handles phase switching, MCU combines results

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
2026-02-01 21:19:57 +13:00
..
HelperTools/SignalIDSamplerates Font-dependent width in toolbar 2020-11-23 13:02:56 +01:00
Integrationtests HIL: more rigorous test of firmware update process 2025-05-31 15:14:19 +02:00
PC_Application add Correlated Double Sampling (CDS) support 2026-01-31 23:47:02 +13:00
VNA_embedded implement FPGA-based CDS to avoid BRAM overflow 2026-02-01 21:19:57 +13:00
.gitignore Some integration tests 2022-11-14 00:09:19 +01:00