GSoC 2025 Final Valuation Report

1. Executive Summary

            Scope Delivered: Implemented three GR4 block families—Math, Analog, and Digital—prioritized over Audio I/O per mentor guidance to unblock core DSP workflows in GNU Radio 4.0.
        

Modern C++23 Template-first, clean CRTP blocks; reflection for runtime config

KISS Kernels Focused processOne() and start()/stop() lifecycles

Robust Testing Boost.UT suites; type-matrix trimmed to keep CI stable

Practical CI CMake targets per subtree; fixes for runner memory limits

Impact & Value

Work surfaced CI and migration realities (Docker OOM, Sonar on forks; fair-acc → gnuradio move), shipped a scrapable GR3→GR4 porting guide, and established reviewable patterns (lean headers, type-safe instantiation, small kernels).

Post-GSoC Commitment: I'll remain available to address reviews and help merge the PRs.

2. Project Links & Resources

Official GSoC Project Page

summerofcode.withgoogle.com/programs/2025/projects/ES4VxTjr

GR4 Development Home

github.com/fair-acc/gnuradio4

Active GR4 development

GR4 Organization Fork

github.com/gnuradio/gnuradio4

Comprehensive Porting Guide

krxgu.github.io/porting-guide-outline.html

HTML/MD, scrapable for contributors & LLMs

Pull Requests (During Coding Phase)

Math Blocks

fair-acc/gnuradio4#595

75% of MATH headers ported; discussion documents CI OOM and test splitting considerations

Analog Blocks

gnuradio/gnuradio4#5

Frequency/Phase Mod, AM/FM demod, AGC(1/2) families + tests

Digital Blocks

gnuradio/gnuradio4#6

Directory tree by use-case; core kernels (e.g., LFSR) and tests seeded

Patch Diffs

Math PR Diff

patch-diff.githubusercontent.com/raw/fair-acc/gnuradio4/pull/595.diff

Analog PR Diff

patch-diff.githubusercontent.com/raw/gnuradio/gnuradio4/pull/5.diff

3. Changes vs. Original Proposal

            Strategic Pivot: Shifted from Audio I/O to Analog, Digital, and Math to maximize GR4 readiness and maintainer priorities.
        

Higher leverage: Unblocks core DSP chains sooner
Contributor onramp: Clearer APIs/tests attract more reviewers
Ecosystem impact: Lays foundations for future ports

4. Technical Contributions

Math Blocks (Port + Extensions)

OPEN

Branch/PR: port-math-block → fair-acc/gnuradio4#595

Delivered Blocks:

Binary: Add / Sub / Mul / Div (+ Const)
Reductions: Max / Min
Bitwise: And / Or / Xor (integral types)
Unary: Negate / Not / Abs
Special: Log10, Integrate (decimating sum), Argmax (index over vlen)

Design & Tests:

Type-safe instantiation lists to limit template bloat
CRTP blocks with processOne / processBulk
Boost.UT coverage for scalar/complex; trimmed type matrix to avoid CI OOM

Size: ~500+ LOC across headers and tests.

Status: CI mostly green; Sonar check on forked PRs blocked by org secrets.

Analog Blocks (AM/FM/PM + AGC Family)

OPEN

Branch/PR: port-analog-block → gnuradio/gnuradio4#5

Implemented Headers:

Modulators: FrequencyMod.hpp, PhaseModulator.hpp
Demodulators: QuadratureDemod.hpp, FmDet.hpp (slope)
Envelope: AmDemod.hpp (IIR smoothing)
Gain Control: Agc.hpp, Agc2.hpp

Tests & Build:

Per-header Boost.UT suites; e2e mod→demod checks
KISS kernels (processOne where 1:1; processBulk for state/decim)

Size: ~1k+ LOC across headers and tests.

Status: Functionally complete; small CI nits (casts/wrapping) pending.

Digital Blocks (Directory Tree + Core Kernels)

OPEN

Branch/PR: port-digital-block → gnuradio/gnuradio4#6

Directory by Use-Case:

digital/
core/       Constellation, Lfsr, Crc, Scrambler, Enums, detail/Bits.hpp
mapping/    ChunksToSymbols, Encoders/SoftDecoders, Diff (enc/dec), Slicers, Map
timing/     MM Clock, Symbol Sync, Costas/FLL/PFB
measure/    MpskSnrEst, EVM, ProbeDensity
equalizer/  AdaptiveAlgorithm, LinearEq, DFE
ofdm/       CP, Serializer, CarrierAllocator, Equalizers, ChanEst, Sync
packet/     Header formats, Header gen/parse, Sink, Demux
misc/       Correlators, BurstShaper, Protocol/HDLC
compat/     Thin 3.x shims, aliasing for continuity

Delivered so far:

LFSR/Scrambler/CRC kernels + Boost.UT
Constellation direction: POD Constellation<N> + stateless slicing/metrics; thin legacy adapters

Build & Tests:

Per-subtree CMake targets for focused CI
Small kernels, STL-first, zero v-tables

Size: ~4k+ LOC (~45 files) in this initial wave.

Status: Structure + P0 kernels landed; large PR will be reviewed by multiple maintainers over several months.

5. Engineering Practices & Lessons

            Summary: Lean kernels, predictable lifecycles, modular CMake, and pragmatic CI made GR4 contributions reviewable and stable.
        

CMake & CI

Per-subtree targets for fast, focused builds
Runner-aware test matrices (trimmed type products; avoid span-of-spans)
Documented decisions in PRs to aid reviewers

Testing Strategy

Boost.UT suites for scalar/complex paths
Direct kernel tests; e2e where valuable

API Design

Reflection + GR_REGISTER_BLOCK for consistent config
processOne()/processBulk() with start()/stop() for state
KISS over inheritance; type-safe instantiation

Documentation

Scrapable GR3→GR4 porting guide (HTML/MD) to onboard contributors and assist LLM tooling

Community

Weekly mentor syncs; responsive PR discussion; rationale recorded in threads

CI Constraints & Technical Context

Understanding these constraints is crucial for future contributors and maintainers working with the GNU Radio 4.0 codebase:

GitHub-Hosted Runners Memory

Standard Configuration: Linux/Windows runners provide ~7 GB RAM standard
Impact: Large template/product tests can stress memory, especially under Docker
Reference: GitHub Docs - Hosted Runners

Secrets on Forked PRs

Default Behavior: By default, secrets aren't passed to workflows triggered from forks
Impact: Scanners like SonarCloud will fail unless maintainers alter policy/flows
Reference: GitHub Docs - Using Secrets

SonarCloud on External PRs

Community Resources: SonarCloud 2025 PR Decoration Issues
Fork PR Limitations: Community Thread on Fork PR Limitations

6. Quantitative Snapshot

Detailed Metrics

Digital PR

~4k+ LOC across the initial wave
~45 files (headers, tests, CMake)
Structured for modular CI and maintainability

Math PR

~500+ LOC across headers and tests
13 commits during coding phase
Extensive tests for scalar/complex paths

Analog PR

~1k+ LOC across headers and tests
11+ commits
Complete AM/FM/PM/AGC family with per-header tests

7. Risks, Challenges, and Resolutions

            Challenge Management: Addressed CI memory, forked-PR scanning limits, and cross-compiler template diagnostics pragmatically.
        

CI Memory on Hosted Runners

Issue: ~7 GB RAM can be exhausted by large template/type products.

Actions: Trimmed type matrices; favored float/double/complex; avoided span-of-spans; modularized tests.

Outcome: Stable runs with representative coverage.

Sonar on Forked PRs

Issue: Secrets are not exposed to forks, blocking Sonar checks.

Actions: Treated as maintainer-side configuration; focused on compiler/functional CI.

Outcome: Clear ownership; unblock merges once org CI is adjusted.

Template Diagnostics (Clang/GCC)

Issue: Noisy diagnostics across toolchains.

Actions: Cleaner concepts/aliases; explicit typedefs; systematic handling of conversions.

Outcome: Clearer errors and consistent builds.

8. What Remains & Next Steps (Post‑GSoC)

            Continued Commitment: While the GSoC coding period has concluded, I remain committed to seeing these contributions through to completion and will continue to support the GNU Radio community.
        

Analog Blocks: Fix the remaining CI test failures (a few lines: casts/wrapping), then merge. This involves addressing minor type casting issues and ensuring all tests pass consistently.
Math Blocks: Finalize CI green by handling the forked‑PR Sonar gap in upstream CI (maintainers) or temporarily skip Sonar on external PRs. This ensures the math blocks can be merged without CI blocking.
Digital Blocks: The large PR will be reviewed by multiple maintainers over several months. This comprehensive review approach allows for thorough evaluation of the entire digital block structure and implementation.
Constellation Implementation: Land the C++23 Constellation<N> with slicing/metric strategies + legacy shims; follow with SIMD hooks for performance optimization.
Migration Coordination: Coordinate PR targets as the project transitions from fair-acc/gnuradio4 → gnuradio/gnuradio4 so work lands in the canonical organization.

Long-term Vision

Beyond the immediate next steps, I envision these contributions serving as a foundation for future GNU Radio 4.0 development, providing:

Reference Implementation: Well-tested, documented examples for future contributors
Porting Patterns: Established workflows for migrating from GR3 to GR4
Community Growth: Lower barrier to entry for new contributors
Performance Baseline: Modern C++23 implementations that can be optimized further

9. Licensing

            Compatibility: I'm comfortable with the licensing required to merge these contributions into the GNU Radio 4.0 repositories.
        

Code is intended for inclusion under GNU Radio's existing licensing practices and is structured to remain compatible with community standards.

10. Acknowledgments

            Community Support: This project would not have been possible without the guidance, support, and collaboration of the GNU Radio community.
        

Mentors

Josh Morman

Primary mentor providing weekly guidance, technical direction, and unblocking support throughout the project.

John Sally

Secondary mentor offering additional technical insights and community perspective.

Community Members

GNU Radio Community: For reviews, early adoption feedback, and maintaining an open, collaborative environment
Element (Matrix) Contributors: For active discussions and technical support on the official communication channels
CI/Infrastructure Team: For maintaining the build and test systems that made this work possible

Future Commitment

I will remain active after GSoC to see these PRs through to merge and help new contributors build on this work. The relationships and knowledge gained during this project will continue to benefit the GNU Radio ecosystem.

11. Current Status & Technical Context

            Current Status: All three major PRs are open and actively being reviewed, with varying levels of completion and CI status.
        

Overview

All contributions are currently in active review phases. The Math and Analog blocks are functionally complete with minor CI adjustments pending, while the Digital blocks represent a comprehensive implementation that will undergo thorough review by multiple maintainers over several months.

This approach ensures quality while respecting the complexity and scope of each contribution. I remain actively engaged in addressing feedback and supporting the review process.

Table of Contents

1. Executive Summary

Impact & Value

2. Project Links & Resources

Official GSoC Project Page

GR4 Development Home

GR4 Organization Fork

Comprehensive Porting Guide

Pull Requests (During Coding Phase)

Math Blocks

Analog Blocks

Digital Blocks

Patch Diffs

Math PR Diff

Analog PR Diff

3. Changes vs. Original Proposal

4. Technical Contributions

Math Blocks (Port + Extensions)

Delivered Blocks:

Design & Tests:

Analog Blocks (AM/FM/PM + AGC Family)

Implemented Headers:

Tests & Build:

Digital Blocks (Directory Tree + Core Kernels)

Directory by Use-Case:

Delivered so far:

Build & Tests:

5. Engineering Practices & Lessons

CMake & CI

Testing Strategy

API Design

Documentation

Community

CI Constraints & Technical Context

GitHub-Hosted Runners Memory

Secrets on Forked PRs

SonarCloud on External PRs

6. Quantitative Snapshot

Detailed Metrics

Digital PR

Math PR

Analog PR

7. Risks, Challenges, and Resolutions

CI Memory on Hosted Runners

Sonar on Forked PRs

Template Diagnostics (Clang/GCC)

8. What Remains & Next Steps (Post‑GSoC)

Long-term Vision

9. Licensing

10. Acknowledgments

Mentors

Community Members

Future Commitment

11. Current Status & Technical Context

Overview