Per keystroke, diff the new frame against the last shown one to find the
changed row band and partial-refresh only those rows instead of all 272.
E-paper update time scales with the gate rows driven, so a single edited
text line refreshes far faster. Windowed in Y only (full width, both
controllers), so the seam/mirroring logic is unchanged. Also drop the
periodic full refresh to every 64 updates — the panel stays visually
clean, so it's now mainly for longevity.
Spike 5 — first spike where keyboard input and panel output run
together. usb_kbd changes from a blocking run() into start(): it brings
the USB host stack up on background threads and pushes edge-detected,
US-layout-translated key-downs onto a queue drained via next_key().
main.rs owns the panel, maintains a wrapped/scrolling text buffer, and
partial-refreshes per keystroke batch with a periodic full refresh to
clear ghosting. Logs per-refresh latency.
display_frame_partial writes the new image to bank 0x24, runs GxEPD2's
partial waveform (_Update_Part: 0x3C/0x80, 0x21/0x00,0x10, 0x22/0xFF,
0x20), then syncs bank 0x26 so the next partial has a correct baseline.
Like GxEPD2 for this dual-controller panel, the update covers the full
panel with the partial waveform — no windowing, since the waveform time
dominates. Much faster than a full refresh and without the flashing.
Spike 4. Drive the ESP-IDF USB Host Library directly through the raw
esp-idf-sys bindings (the convenience HID class driver is a managed
component not vendored in mainline, and a boot keyboard doesn't need
it). On attach, src/usb_kbd.rs enumerates the device and dumps its
descriptors, claims the boot-keyboard interface, sends SET_PROTOCOL(boot)
and SET_IDLE(0), then polls the interrupt-IN endpoint and decodes each
8-byte report into modifiers + keycodes logged over UART.
main.rs becomes the Spike 4 harness; the epd module is kept compiled
(allow(dead_code)) so it doesn't bit-rot. Verified on hardware with a
19f5:3255 keyboard: letters, digits, modifiers, and rollover all decode.
Add a thin dual-SSD1683 driver (src/epd.rs, ported from GxEPD2's
GxEPD2_579_GDEY0579T93) for the 792x272 e-paper panel: reset/init,
RAM addressing, the split-and-mirror full-frame blit across the
master/slave seam at x=396, and full-refresh waveform. Frame
implements embedded-graphics' DrawTarget.
Replace the Spike 1 blink harness in main.rs with the Spike 2 test:
SPI at 4 MHz over SCK 12 / DIN 11 / CS 7 / DC 6 / RST 5 / BUSY 4,
alternating normal/inverted frames with a seam-straddling circle,
"Typoena", and the build tag. Verified on hardware 2026-07-04.
Emit BUILD_TIME and BUILD_GIT (git describe --always --dirty) as
rustc env vars so the running firmware can identify itself on serial
and on-panel. A rerun-if-changed on a nonexistent file forces the
script every build, keeping the timestamp fresh. Bring-up lesson:
know which build you're diagnosing.
The bench board is a DevKitC-1 v1.0 (RGB LED on GPIO 48), not the v1.1
layout (GPIO 38). Vendor the official v1.0 pinout diagram under docs/ and
reference it from the README so the pinout is pinned offline, and fold in
the 2026-07-04 on-hardware blink verification note.
The DevKitC-1 has no discrete LED on GPIO 2, so the Spike 1 blink was
invisible without external wiring. Drive the on-board addressable LED
(WS2812 on GPIO 48) each cycle for visible confirmation on the bench.
Generated from esp-rs/esp-idf-template for the ESP32-S3 std target.
src/main.rs toggles GPIO 2 every 500 ms and logs `blink N` over USB-
serial — the minimum bring-up surface called out in
docs/v0.1-mvp-technical.md (Spike 1: confirm toolchain, flash, and basic
GPIO). edition=2024 with rust-version=1.85.
No editor/render/git/usb/fs modules yet; those land per the spike
methodology when later spikes need them.
