docs(hardware): switch display to GDEY0579T93 with DESPI-c579
Strip-aspect 5.79" panel (792×272) replaces the page-shaped 7.5" choice. Reflows the v0.1 screen layout, framebuffer memory budget, and spike 2 acceptance to validate the SSD1683-class controller path or fall back to a ~300 LoC custom embedded-hal driver.
This commit is contained in:
Julien Calixte
13
README.md
13
README.md
@@ -31,15 +31,18 @@ push) is offered.
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| Part | Choice | Why |
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| MCU | **ESP32-S3-N16R8** (16 MB flash, 8 MB octal PSRAM) | USB OTG host (for the keyboard), Wi-Fi, BLE, dual core @ 240 MHz, plenty of PSRAM for git pack data and screen buffer. Best-supported Rust target in the ESP family. |
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| Display | **Waveshare 7.5" V2 SPI (800×480)** for MVP | Partial refresh works, well-supported by `epd-waveshare`, low power, no IT8951 controller board needed. Upgrade path: 10.3" + IT8951 once UX is proven. |
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| Display | **GDEY0579T93 + DESPI-c579 breakout** (5.79", 792×272, 1-bit) | Good Display panel matched with its own FPC breakout. Strip aspect (~2.9:1) — Freewrite-coded: ~12 lines of edit area, ~95 cols. Tiny framebuffer (~27 KB) leaves PSRAM headroom. The DESPI-c579 is a passive level-shifter / FPC-to-header board, not an active controller — driven over plain SPI like any other epd. |
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| Keyboard | **Nuphy Air60/Halo65 wired USB-C** | ESP32-S3 acts as USB host via TinyUSB. BLE-HID is a fallback but contends with Wi-Fi for radio time during push. |
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| Storage | microSD over SPI | Holds both the git working copy (`/sd/repo/`) **and** the local-only scratch space (`/sd/local/`). Internal flash is for firmware + config only. |
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| Power | **USB-C wall power for MVP**, 18650 + IP5306 in Phase 3 | Measure power profile on real hardware before sizing the battery. E-ink + sleep should give multi-day battery life but battery introduces charging, safety, and BMS complexity we don't need on day one. |
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| Enclosure | 3D-printed, hinged lid | Phase 4 concern. |
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**Why not the 10.3" parallel screen for MVP:** IT8951 driver is fine but adds
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~$80 BOM and parallel pins eat the GPIO budget we want for SD + status LEDs.
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Start cheap, prove the loop, then upgrade.
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**Why the 5.79" strip aspect:** less screen than a 7.5" page-shaped panel,
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but the long-narrow shape biases toward "current line + recent context" —
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the writing posture we actually want. The smaller framebuffer is cheap on
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RAM, and SPI panels keep the GPIO budget open for SD + future peripherals.
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A larger panel (10.3" via IT8951) stays on the table for v1.x once UX is
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proven.
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---
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@@ -51,7 +54,7 @@ rejected alternatives below.
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| Layer | Crate / Component | Notes |
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| HAL / runtime | `esp-idf-svc`, `esp-idf-hal` | std build, gives us heap, threads, VFS, mbedtls, Wi-Fi stack. |
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| Display | `embedded-graphics` + `epd-waveshare` | Pixel framebuffer with partial-refresh regions. We track dirty rects ourselves. |
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| Display | `embedded-graphics` + `epd-waveshare` (or custom driver) | Pixel framebuffer with partial-refresh regions. We track dirty rects ourselves. The GDEY0579T93 uses an SSD1683-class controller; if it's not already in `epd-waveshare`, we write a small driver against `embedded-hal` SPI — ~300 LoC, low risk. |
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| Editor core | Custom, in-tree | Rope buffer (`ropey`), mode state machine, Vim keymap table. |
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| TUI-style layout | Custom thin layer (~500 LoC) | API inspired by Ratatui (`Layout`, `Block`, `Paragraph`) but renders directly to `embedded-graphics`. See below. |
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| USB host | `esp-idf` TinyUSB bindings | Boot-protocol HID is enough for the keyboard. |
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@@ -96,34 +96,46 @@ create remote repos.
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## Screen layout
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Waveshare 7.5" V2 — 800×480, 1-bit.
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GDEY0579T93 — 5.79", **792×272**, 1-bit, partial refresh capable. Wide
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strip aspect (~2.9:1) — biases the UX toward "current line and recent
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context," not a full page.
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```
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┌──────────────────────────────────────────────────────────────┐
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│ notes.md ● 14:02:33 │ ← header (1 line)
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├──────────────────────────────────────────────────────────────┤
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│ │
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│ Lorem ipsum dolor sit amet, consectetur adipiscing elit. │
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│ Sed do eiusmod tempor incididunt ut labore et dolore magna │
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│ aliqua. │
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│ │ ← edit area
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│ The quick brown fox jumps over the lazy▎ │ (cursor block)
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│ │
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│ ... │
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│ │
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├──────────────────────────────────────────────────────────────┤
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│ INSERT • unsaved • Wi-Fi ✓ │ ← status (1 line)
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└──────────────────────────────────────────────────────────────┘
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┌─────────────────────────────────────────────────────────────────────────────────────┐
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│ notes.md ● 14:02:33 │ ← header
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├─────────────────────────────────────────────────────────────────────────────────────┤
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│ Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor │
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│ incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud │
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│ exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. │
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│ │
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│ Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu │
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│ fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in │ ← edit area
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│ culpa qui officia deserunt mollit anim id est laborum. │ (~11 lines)
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│ │
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│ The quick brown fox jumps over the lazy▎ │ (cursor block)
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│ │
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│ │
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│ │
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├─────────────────────────────────────────────────────────────────────────────────────┤
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│ INSERT • unsaved • Wi-Fi ✓ │ ← status
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└─────────────────────────────────────────────────────────────────────────────────────┘
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```
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- Header: filename, dirty indicator (●/○), wall clock if Wi-Fi has set time.
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- Header: filename, dirty indicator (●/○), wall clock if SNTP has set time.
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- Status: mode (always `INSERT` in v0.1), save state, Wi-Fi state. After a
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`Ctrl-S` / `Ctrl-G`, status briefly shows the action result (saved at /
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pushed `abc1234` / error message) then returns to default.
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- Cursor: solid block at the insertion point. **No blink.**
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Fonts: one mono font, embedded in firmware. Probably IBM Plex Mono at a size
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that gives ~70 columns and ~25 lines of edit area.
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Fonts: one mono font, embedded in firmware. Target sizing: a 14 px mono
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glyph at roughly 8 px advance gives ~95 columns × ~11 visible lines of edit
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area after header (16 px) and status (16 px) bars. Final size tuned during
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spike 2 against real legibility on the panel.
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**UX consequence of the strip aspect:** the cursor stays near the bottom of
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the visible area during normal typing; the edit area scrolls one line at a
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time. There is no "page" — just a continuously advancing strip. Embrace it,
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don't fight it.
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## Error UX
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@@ -73,8 +73,11 @@ We do **not** try to build the whole stack and turn it on. Each spike below
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is a small program that proves one risk before we commit to the next layer.
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1. **Spike 1 — Blink.** Confirm toolchain, flash, and basic GPIO.
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2. **Spike 2 — EPD.** Drive the 7.5" panel with `epd-waveshare`; full refresh
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"hello world." Validates SPI wiring, panel timings.
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2. **Spike 2 — EPD.** Drive the GDEY0579T93 (via DESPI-c579 breakout) over
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SPI; full refresh "hello world." Validates SPI wiring, panel timings, and
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— critically — whether `epd-waveshare` already supports the panel's
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controller (SSD1683-class) or whether we write a thin custom driver
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against `embedded-hal`. Either way, ~300 LoC; this spike answers which.
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3. **Spike 3 — SD.** Mount FAT, read/write a file. Validates SPI sharing with
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EPD (or separate bus if needed).
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4. **Spike 4 — USB host.** Enumerate the Nuphy as a boot-protocol HID
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@@ -173,7 +176,7 @@ ESP32-S3-N16R8: 512 KB SRAM + 8 MB PSRAM. We budget conservatively.
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|---|---|---|
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| Internal SRAM | ~120 KB | task stacks, DMA buffers, hot code paths |
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| Internal SRAM | ~80 KB | mbedtls runtime (TLS handshake working set) |
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| PSRAM | ~256 KB | EPD framebuffer (800×480×1 = 48 KB) + shadow + glyph cache |
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| PSRAM | ~128 KB | EPD framebuffer (792×272×1 ≈ 27 KB) + shadow + glyph cache |
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| PSRAM | ~512 KB | rope buffer + edit history headroom |
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| PSRAM | ~1.5 MB | gitoxide working set during push (pack delta, etc.) |
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| PSRAM | rest | heap headroom |
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