# EPD Reference Driver — GDEY075T7 (UC8179)

## Source

**Repository:** [ekosboard/firmware](https://github.com/ekosboard/firmware)  
**File:** [`src/components/EPD/driver/epd_GDEY075T7.c`](https://github.com/ekosboard/firmware/blob/main/src/components/EPD/driver/epd_GDEY075T7.c)

## Panel Info

- **Controller:** UC8179
- **Panel:** GDEY075T7 (Good Display 7.5" B/W, 800×480)
- **Platform:** ESP-IDF (native SPI)
- **Grayscale:** 4-level support present but marked as "NOT TESTED"

## Key Implementation Details

### BUSY Pin Polarity
- **Reference driver:** HIGH = Busy, LOW = Idle
- **⚠️ Our board is INVERTED:** LOW = Busy, HIGH = Idle
- Wait loop polls `gpio_get_level(BUSY) == 0` to detect idle (reference)
- Our code uses `== 0` to wait while busy (opposite meaning, same code pattern)

### Clear Screen (White)
- Writes `0xFF` to **both** old (0x10) and new (0x13) data layers
- `0xFF` = White, `0x00` = Black

### Display Image
- Writes `0x00` to old data layer (0x10) — assumes previous state was black
- Writes actual image data to new data layer (0x13)

### Sleep Sequence
1. `0x50` with `0xF7` — VCOM and data interval setting before sleep
2. `0x02` — Power Off
3. Wait for BUSY idle
4. `0x07` + `0xA5` — Deep Sleep

### Init Sequence (Full Refresh)
1. Hardware reset (RST low 10ms, high 10ms)
2. `0x01` — Power Setting: VGH=20V, VGL=-20V, VDH=15V, VDL=-15V, VDHR=4.2V
3. `0x06` — Booster Soft Start: 0x17, 0x17, 0x28, 0x17
4. `0x04` — Power On + 100ms delay + wait busy
5. `0x00` — Panel Setting: `0x1F` (KW B/W mode)
6. `0x61` — Resolution: 800×480
7. `0x15` — DUSPI disabled
8. `0x50` — VCOM: 0x10, 0x07
9. `0x60` — TCON: 0x22
10. `0xE3` — PWS: 0x22

### Fast Refresh
- `0xE0` → `0x02` (enable fast mode)
- `0xE5` → `0x5A` (fast refresh timing)

### Partial Update
- Uses `0x91` (partial in) / `0x92` (partial out) + `0x90` (resolution setting)
- Writes `~data` (inverted) to old layer to force transitions
- Sets `0x50` → `0x21` (N2OCP disabled) for partial mode

### 4-Level Grayscale
- Requires different booster settings: `0x27, 0x27, 0x18, 0x17`
- `0xE5` → `0x5F` for grayscale timing
- Data encoding: 2 bits per pixel (0xC0=white, 0x00=black, 0x80=gray1, 0x40=gray2)
- Old layer and new layer encode different bit planes, both inverted (`~temp3`)