GSoC 2025 · GNU Radio 4.0 Block-Set Expansion

Week-9 check-in (mentor — Josh Morman)

   
Date 10 July 2025, 17:00 IST
Duration 45 min
Participants Josh Morman · Krish Gupta

1 · Progress update

  • Analog PR Status
    • All CI tests now passing after fixing type casting issues
    • Waiting for final approval from maintainers
    • Minor documentation improvements added
  • Digital Blocks
    • Finalized directory structure for all digital components
    • Completed core components implementation:
      • Lfsr.hpp, Crc.hpp, Scrambler.hpp, Bits.hpp
      • Constellation<N> with all common mappings
      • ChunksToSymbols and SymbolsToChunks
    • Set up CI configuration for digital module with focused test matrices

2 · Digital Directory Structure

Finalized the directory structure for the digital module:

digital/
├── core/          # Core components (LFSR, CRC, Scrambler, etc.)
│   ├── Lfsr.hpp
│   ├── Crc.hpp
│   ├── Scrambler.hpp
│   ├── Constellation.hpp
│   └── detail/
│       └── Bits.hpp  # Bit manipulation utilities
├── mapping/       # Symbol mapping and slicing
│   ├── ChunksToSymbols.hpp
│   ├── SymbolsToChunks.hpp
│   ├── DifferentialEncoder.hpp
│   └── DifferentialDecoder.hpp
├── timing/        # Clock recovery, synchronization
├── measure/       # SNR estimation, EVM, etc.
├── equalizer/     # Channel equalization
├── ofdm/          # OFDM-specific components
├── packet/        # Packet handling
├── misc/          # Miscellaneous utilities
└── compat/        # Compatibility with GR3

This organization:

  • Groups related functionality together
  • Provides clear boundaries between subsystems
  • Supports focused testing and CI
  • Enables incremental development

3 · CI Configuration for Digital PR

Implemented a specialized CI configuration for the digital module:

# .github/workflows/digital.yml
jobs:
  core:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Build and test core
        run: |
          cmake -B build -DBUILD_TESTING=ON -DGR4_DIGITAL_CORE_ONLY=ON
          cmake --build build --target gr4_digital_core_test
          cd build && ctest -R "digital_core" -V

  mapping:
    needs: core
    runs-on: ubuntu-latest
    steps:
      # Similar structure, focused on mapping tests
      
  # Additional jobs for other components

This approach:

  • Focuses testing on specific components
  • Reduces memory pressure
  • Provides faster feedback on PRs
  • Makes it easier to identify failures

4 · Implementation Highlights

Bits Utility Class

Created a utilities class for efficient bit manipulation:

namespace gr::digital::detail {

class Bits {
public:
    // Pack bits into bytes (MSB or LSB first)
    template <typename InputIt, typename OutputIt>
    static void pack(InputIt first, InputIt last, 
                     OutputIt d_first, bool msb_first = true);
    
    // Unpack bytes into bits
    template <typename InputIt, typename OutputIt>
    static void unpack(InputIt first, InputIt last,
                      OutputIt d_first, bool msb_first = true);
    
    // Count set bits in a value
    template <typename T>
    static constexpr int popcount(T value);
    
    // Reverse bit order
    template <typename T>
    static constexpr T reverse(T value);
};

} // namespace gr::digital::detail

This utility class provides building blocks for many digital components.

5 · Addressing Sonar on Forked PRs

Discussed strategies for handling the Sonar CI issue with forked PRs:

Option Pros Cons
Skip Sonar checks Unblocks merges Misses quality checks
Maintainer adjusts CI Preserves all checks Requires organization changes
Clone PR manually Works with current system Extra maintainer effort

Josh mentioned:

“For the Digital PR, I’m working with the CI team to temporarily adjust the workflow configuration to allow Sonar checks on external PRs. This should unblock the Math PR as well.”

6 · Action items

Owner Task
Krish • Prepare and submit Digital blocks PR
• Continue implementing remaining digital components
• Update test coverage for edge cases
Josh • Coordinate with CI team on Sonar issues
• Review Digital core components
• Facilitate final approval of Analog PR

Next sync: July 17th to review Digital PR and discuss remaining implementation priorities.

7 · Key Decisions

Several important decisions were made during this week’s development:

  1. Focus on quality over quantity - Prioritize robust implementations of core components
  2. Modular directory structure - Organize by functionality for better maintainability
  3. Focused CI configuration - Optimize CI for faster feedback and better resource usage
  4. Documentation-first approach - Ensure all components are well-documented
  5. Type-safe interfaces - Use modern C++ features for safer APIs

These decisions align with the project’s goal of creating a maintainable, high-performance block set for GNU Radio 4.0.