Develop

Build a time-aware screen

An Einq app is firmware logic that decides what to draw and when to refresh e-paper. The canonical example: show the current time and weekday, re-render on the hour, and swap layout or copy at day boundaries.

1. Hardware & stack

Xteink X4 (ESP32-C3, 4.3″ e-paper). Einq is not a reader — no book UI. Firmware uses the open X4 community SDK (display, buttons, power). CrossPoint was optional bring-up; new apps live in this repo under apps/.

2. Programming model

• Render — compose a framebuffer (text, bitmaps, simple shapes). E-paper likes high contrast and infrequent updates.
• Schedule — wake on RTC alarm, timer, or light sleep until the next boundary (hour, sunrise, cron rule).
• Refresh policy — partial refresh when only digits change; full refresh at day change or ghosting threshold.
• Power — deep sleep between updates; WiFi only when syncing content.

3. Sketch: screen as f(day, time)

Pseudocode for a clock face app:

void loop() {
  DateTime now = rtc.now();
  if (needs_full_refresh(now)) {
    draw_day_header(now);      // weekday, optional quote
    draw_time_large(now);
    eink.fullUpdate();
  } else if (minute_changed(now)) {
    draw_time_large(now);      // partial update region
    eink.partialUpdate(time_region);
  }
  sleep_until(next_event(now)); // e.g. next hour or next minute
}

Event next_event(DateTime t) {
  if (t.minute() == 0) return top_of_hour(t);
  return next_minute(t);
}

Real implementations live in PlatformIO/C++ against CrossPoint’s display drivers. We will add a reference app under apps/clock-face/ as the tree matures.

4. Repo layout

einq/
  apps/           # one folder per Einq app
  firmware/       # shared helpers, board notes
  docs/           # this site

5. Contribute

Open issues and PRs on CastaliaInstitute/einq. For CrossPoint bugs or reader features, contribute upstream.