Two intertwined bugs were leaving every ESP32 ePaper example broken
end-to-end. Only the 5.65" UC8159c panel surfaced the failure
audibly ("Busy Timeout!" repeating in serial), because its inverted
busy polarity caused the firmware to hang inside `_waitBusy()`. The
SSD168x ePaper examples APPEARED to run cleanly but never actually
rendered anything to the panel — the canvas stayed at the idle paper
colour because the same registration path was broken.
Root cause #1 — `setSensors` was a full REPLACE, not a merge.
`Esp32Bridge.setSensors(sensors)` did `this._pendingSensors =
sensors`. At `startBoard()` time the store iterates components,
resolves wires for any entry in `SENSOR_COMPONENT_MAP` (DHT22 /
HC-SR04 / I²C sensors) and calls `setSensors(...)` with that list.
ePaper components live in `PartSimulationRegistry` (not in the
sensor map) and are registered via `sendSensorAttach()` AT
COMPONENT-MOUNT TIME — well before `startBoard()` runs. Full-replace
semantics blew that registration away on every Run click, so the
worker never instantiated an `Ssd168xEpaperSlave` / `Uc8159cEpaperSlave`,
no SPI bytes were decoded, no frames were latched, and BUSY was
never driven.
Fix: upsert by `pin` so pre-existing registrations from
PartSimulationRegistry handlers are preserved alongside the
startBoard-resolved sensors. Confirmed via a WebSocket spy that the
`start_esp32` payload now carries the ePaper sensor entry.
Root cause #2 — BUSY polarity was hard-coded for SSD168x only.
Verified against upstream GxEPD2 source:
* SSD168x family — constructor passes `_busy_level = HIGH`
→ BUSY=HIGH means busy, LOW means ready.
* UC8159c family — constructor passes `_busy_level = LOW`
→ BUSY=LOW means busy, HIGH means ready.
The worker only drove BUSY after a frame flush (and at the wrong
polarity for UC8159c), so the firmware's first `_waitBusy()` inside
`_PowerOn()` / `_InitDisplay()` — which fires BEFORE any frame —
blocked for the full 25 s `_busy_timeout`.
Fix: read `controller_family` from the registration payload, pick the
per-family idle level, and (a) seed the pin to IDLE at registration so
the first `_waitBusy()` sees "ready" immediately, (b) use that
polarity (idle vs. busy) when pulsing on frame flush.
Verified on https://velxio.dev/example/epaper-5in65-7c-esp32-rainbow:
the serial timeline now reads `_InitDisplay reset : 1566` /
`_PowerOn : 148` / `_PowerOff : 183` / `frame done` (all sub-2 ms
busy-waits, no timeouts). Sensor registration confirmed via the
`start_esp32` payload carrying the `epaper-ssd168x` entry.
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