GSoC 2025 · GNU Radio 4.0 Block-Set Expansion

Week-4 check-in (mentor — Josh Morman)

   
Date 5 June 2025, 17:00 IST
Duration 45 min
Participants Josh Morman · Krish Gupta

1 · Progress update

  • Math blocks
    • 100% of MATH headers now ported with successful compilation on both GCC 14 and Clang 17
    • Created PR fair-acc/gnuradio4#595 for Math blocks
    • Completed Conjugate SIMD implementation with proper specializations for complex types
    • Finished Log10 block with edge case handling for negative inputs and NaN/Inf
  • CI workflow
    • Discovered memory constraints in GitHub Actions runners (~7GB RAM)
    • Large template instantiation matrices causing OOM errors in Docker builds

2 · CI Memory Constraints

Identified root causes of CI memory issues:

// Original approach causing memory issues
using TestTypes = std::tuple<
    int8_t, int16_t, int32_t, int64_t,
    uint8_t, uint16_t, uint32_t, uint64_t,
    float, double, 
    std::complex<float>, std::complex<double>,
    std::complex<int16_t>, std::complex<int32_t>
>;

Solution:

// More focused test matrix to reduce memory pressure
using PriorityTypes = std::tuple<
    float, double,
    std::complex<float>, std::complex<double>,
    int32_t, int16_t // Most common integer types
>;
  • Trimmed type matrices to focus on most common types
  • Added selective testing for integer variants
  • Improved compiler diagnostic messages by using explicit template instantiations

3 · Analog Block Planning

Started design for Analog blocks with key considerations:

Block Family Design Approach Implementation Status
Modulators CRTP pattern with processOne() Planning stage
Demodulators State management via start()/stop() Planning stage
AGC IIR-based approach with optimized gain calculation Initial research

Josh suggested we pivot from the original Audio I/O focus to prioritize core DSP blocks:

“Analog and Digital blocks will unblock more users than Audio I/O. Let’s focus there first, as they’re the building blocks of most flowgraphs.”

4 · Porting Guide Progress

Started work on a comprehensive porting guide:

  • Documented the templating pattern used in Math blocks
  • Created sections for reflection macro usage
  • Added example transformation of GR3 → GR4 API
  • Planning to make it scrapable for future contributors and LLMs

5 · Action items

Owner Task
Krish • Address CI feedback on Math PR
• Begin implementation of FrequencyMod and PhaseModulator
• Continue work on porting guide
Josh • Review Math PR
• Coordinate with maintainers on CI memory issues
• Provide sample code for AGC block patterns

Next sync: June 12th to review Analog block progress and discuss Digital block directory structure.

6 · Technical Notes

Key learnings from this week:

  • Template instantiation can quickly explode memory usage in C++23
  • CI Docker environments add overhead that further constrains available memory
  • CRTP (Curiously Recurring Template Pattern) provides static polymorphism without virtual overhead
  • Type matrices need careful pruning to ensure CI stability without sacrificing coverage