# DECISIONS.md — clar200-unlock Decision Log

Project-specific decisions. For global/cross-cutting decisions, see `~/bin/DECISIONS.md`.

Format: `YYYY-MM-DD: <decision> — <why>`

## Architecture

- 2026-06-14: Use the drive's **F3 service UART**, not any SCSI path — every SCSI
  command (incl. READ CAPACITY) returns Hardware Error on these EMC-locked drives;
  F3 bypasses the SCSI layer. (See EMC_CLAR200_DRIVE_FIX_NOTES.md for the
  exhaustive SCSI-side failure list.)
- 2026-06-14: **ESP32-C3 as the USB-serial bridge** rather than buying a USB-TTL
  module — one is already attached to steel141 (`/dev/ttyACM0`) and its 3.3 V
  logic is a native match for the F3 header (many FTDI cables are 5 V = unsafe).
- 2026-06-14: Bridge uses the C3's **native USB-CDC** as host side + **UART1
  (GPIO4 TX / GPIO5 RX)** to the drive, with a live `~N` baud menu so baud can be
  swept without reflashing.

## Implementation

- 2026-06-14: Build flag `CDCOnBoot=cdc` is **required** so `Serial` maps to
  USB-CDC, not UART0; encoded in `firmware/flash.sh` FQBN.
- 2026-06-14: F3 format commands are **discovered via `?`**, not copied from
  7200.11 forums — Exos X18 dialect differs and wrong `m0,...` params can worsen
  a drive.

## Deferred / Rejected
<!-- Decisions NOT to do something are just as valuable -- prevents re-proposing rejected ideas -->

- 2026-06-14: **Rejected** further SCSI-level attempts (sg_format flag variants,
  firmware download, sanitize) — prior session exhausted them; all return
  Hardware Error because the EMC firmware refuses below the command layer.
- 2026-06-14: **Rejected** doing F3 work with the drive in the pve173 JBOD —
  too risky next to live tank; bench-only.
- 2026-06-14: **Deferred** the BSY isolation/tape trick — the drive boots and
  answers INQUIRY (not BSY-hung), so it's unlikely to be needed; contingency only.
- 2026-06-14: **Not yet decided** — whether to RMA to ServerPartDeals first vs.
  attempt F3 first. Leaning: attempt F3 (cable is free + already here), RMA as
  fallback if F3 refuses.