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Kaj SchittecatandClaude Opus 4.8
3bf56cdd37
Root cause, established by on-device elimination over one long session: SD-card WRITE bursts electrically disturb the T-Display P4's AMOLED -- the whole-screen blue flash of #167. The display stack itself measured clean at every layer while flashes were visible: framebuffer content (flush tracer: every band black), DSI bridge underrun interrupt (never fired), DSI host protocol errors incl. the host payload-buffer underflow (never latched), DCS/brightness traffic and XL9535 expander writes (silent), disp on/off (never). The flash survived every digital derate -- 4->1-bit SD bus, 20->10 MHz SD clock, 1000->750 Mbps DSI lane rate -- on every card tried, at any brightness (including near-zero, i.e. the panel is being upset at the hardware level, not showing content), yet vanished the moment the card was removed or left unwritten. The card's rail is switched off the same 3V3 domain as the panel (XL9535 SD_EN), so its program-current spikes reach the panel and no firmware setting can filter them. Streaming tile writes never flashed; rapid open-write-close store bursts always did. Meck-P4 not flashing proves nothing about the board: it never writes the SD. Fix: the hot store (contacts/channels/identity/blobs/prefs-file/chat history) lives on the INTERNAL 'storage' partition; the SD keeps bulk, gentle writers (map tiles, backups). The internal partition is mounted as LittleFS, not FAT: the P4's FAT layer has documented broken metadata and the v3 migration proved its writes are no better (a 102 KB contacts3 "copied" onto it read back as 0 B; on LittleFS the same copy reads back byte-exact and loads all 689 contacts). esp_littlefs looks partitions up by label with SUBTYPE_ANY, so the ex-FAT partition converts in place on first boot (formatOnFail) -- no partition-table change, OTA-safe. One-time v4 migration (lessons v1-v3 encoded): substance-gated (only from a card whose contacts3 beats the internal one -- a fresh test card once donated a blank store), whitelist-only copy (v2 filled the partition with junk before contacts3 landed), both historical card layouts probed (root vs /meshcomod), marker written only after the copy, card never written (it remains the rollback). Also in this change, kept as opt-in diagnostics (dormant without their env gates): WADA_P4_POKE_TRACE (DCS/expander/disp-on-off tracing + a DSI host error-register poller), WADA_SD_KHZ / WADA_SD_1BIT (SD primary-rung derates), WADA_DSI_MBPS (lane-rate override; default back at the vendor 1000 -- the 750 experiment changed nothing and is documented in the driver). Verified on device: no flash on the contact-churn trigger with the store internal (the previously 100%-reproducing trigger), 689/689 contacts after migration, tiles still on SD. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>