Debugging

A sequel to the first STM32H750 tracker post. After the C++ port was proven in production, I spent a week of evenings cutting dead vendor code, splitting the algorithm out to host for unit tests, wiring the LCD SPI through DMA to let the CPU run the tracker in parallel with the blit, unlocking the camera’s real frame rate, chasing a subtle BB-drift bug back to a too-wide SAD search, and finally building an offline A/B harness that compares SAD, NCC, and MOSSE on four synthetic scenarios so the next tracker port is a data decision, not a vibes one.

A long, honest retrospective on turning a WeAct STM32H750 board, a cheap OV7725 IR camera, and an Xbox controller into a live template-matching tracker. Every dead end, every wrong assumption, every fix — and what I’d do differently next time.

Working through six C++ problems modeled on Optiver’s Senior SWE assessment: supermarket checkout simulation, order book matching, dividend pricing, lattice path DP, Dijkstra with K free edges, and a price-alert router built twice — AoS first, then SoA. Every bug, wrong turn, and data structure tradeoff included.

DDS content filter parameter substitution (%0, %1) silently fails for string fields in ROS 2 with Fast DDS. The root cause is three layers deep — the DDS SQL grammar requires quoted string literals, but no ROS 2 layer adds the quotes. Here’s how I traced it and where to fix it.

Four bugs in GStreamer’s shmsink/shmsrc elements — a race condition, a use-after-free, a wrong-pointer dereference, and a page alignment mismatch. What they have in common, how to find them, and what they teach about writing correct GStreamer elements.

A 2-line fix for a race condition in GStreamer’s shmsink that causes every pipeline using shared memory to exit with an error. How I found it, proved it, and verified the fix with sanitizers.

Everything I learned contributing 6 PRs to PX4-Autopilot in a single session — from Docker-based builds and sanitizer workflows, through uXRCE-DDS session debugging and MAVLink signing analysis, to SITL integration testing. Real bugs, real fixes, real build output.

A three-day odyssey connecting PX4 flight controller to a GPU-rendered Unity drone simulation running headless inside Docker — through licensing labyrinths, shader abysses, coordinate system riddles, native library dragons, and a TCP protocol twist ending nobody expected.

Eigen’s .inc plugin headers were read by Doxygen but never preprocessed as C++ — meaning macros like EIGEN_PARSED_BY_DOXYGEN were silently ignored. Here’s how I verified it in Docker and what the one-line fix looks like.

A day-long battle fixing a CI pipeline that builds Docker images on a self-hosted Jetson Xavier runner. From stale git submodules to GCC-15 assembler errors, expired tokens, DNS failures inside Docker, and deleted upstream branches — every layer of the stack had something broken.