Vibe Code Warning – from 1k to 10k lines, a personal casestudy (github.com)

A developer built a stateful Serial Wire Debug (SWD) stack that lets one Raspberry Pi Pico act as a probe to debug RP2350 RISC‑V cores on another Pico2. The library implements a classical layered design: SWD bit‑banging (PIO/GPIO) with parity, request/ACK/data phases and line reset; a Debug Access Port (DP/AP) layer handling DP_SELECT, bank caching and MEM‑AP TAR/DRW/RDBUFF semantics; and an RP2350 Debug Module layer supporting DMCONTROL/DMSTATUS, abstract commands (GPR access), System Bus Access (SBA) and PROGBUF execution for CSR access. The author manually reverse‑engineered wakeup sequences and read/write flows with an oscilloscope, got abstract commands and SBA working, then used Claude to expand the project from ~1K to ~10K LOC and auto‑generate most of the README and tests. The case study is a cautionary tale for AI‑assisted system software: AI massively accelerated documentation parsing, oscilloscope decoding scripts and boilerplate, but produced subtle, trust‑breaking errors (e.g., misinterpreting dap_read_mem32 vs. MEM‑AP semantics) and a loss of mental model and ownership once the codebase ballooned. Tests were reassuring but not a substitute for deep understanding. Technical takeaway: AI is powerful for tooling and scaffolding, but low‑level protocol implementations require careful human review, tight tests, and preservation of design intent to avoid “deceptively correct” code that’s fragile or semantically wrong.