# CrossPoint Reader

Firmware for the **Xteink X4** e-paper display reader (unaffiliated with Xteink).
Built using **PlatformIO** and targeting the **ESP32-C3** microcontroller.

CrossPoint Reader is a purpose-built firmware designed to be a drop-in, fully open-source replacement for the official 
Xteink firmware. It aims to match or improve upon the standard EPUB reading experience.

![](./docs/cover.jpg)

## Motivation

E-paper devices are fantastic for reading, but most commercially available readers are closed systems with limited 
customisation. The **Xteink X4** is an affordable, e-paper device, however the official firmware remains closed.
CrossPoint exists partly as a fun side-project and partly to open up the ecosystem and truely unlock the device's
potential.

CrossPoint Reader aims to:
* Provide a **fully open-source alternative** to the official firmware.
* Offer a **document reader** capable of handling EPUB content on constrained hardware.
* Support **customisable font, layout, and display** options.
* Run purely on the **Xteink X4 hardware**.

This project is **not affiliated with Xteink**; it's built as a community project.

## Features

- [x] EPUB parsing and rendering
- [x] Saved reading position
- [ ] File explorer with file picker
  - [x] Basic EPUB picker from root directory
  - [x] Support nested folders
  - [ ] EPUB picker with cover art
- [ ] Image support within EPUB
- [ ] Configurable font, layout, and display options
- [ ] WiFi connectivity
- [ ] BLE connectivity

## Installing

### Web (latest firmware)

1. Connect your Xteink X4 to your computer via USB-C
2. Go to https://xteink.dve.al/ and click "Flash CrossPoint firmware"

To revert back to the official firmware, you can flash the latest official firmware from https://xteink.dve.al/, or swap
back to the other partition using the "Swap boot partition" button here https://xteink.dve.al/debug.

### Web (specific firmware version)

1. Connect your Xteink X4 to your computer via USB-C
2. Download the `firmware.bin` file from the release of your choice via the [releases page](https://github.com/daveallie/crosspoint-reader/releases)
3. Go to https://xteink.dve.al/ and flash the firmware file using the "OTA fast flash controls" section

To revert back to the official firmware, you can flash the latest official firmware from https://xteink.dve.al/, or swap
back to the other partition using the "Swap boot partition" button here https://xteink.dve.al/debug.

### Manual

See [Development](#development) below.

## Development

### Prerequisites

* **PlatformIO Core** (`pio`) or **VS Code + PlatformIO IDE**
* Python 3.8+
* USB-C cable for flashing the ESP32-C3
* Xteink X4

### Checking out the code

CrossPoint uses PlatformIO for building and flashing the firmware. To get started, clone the repository:

```
git clone --recursive https://github.com/daveallie/crosspoint-reader

# Or, if you've already cloned without --recursive:
git submodule update --init --recursive
```

### Flashing your device

Connect your Xteink X4 to your computer via USB-C and run the following command.

```sh
pio run --target upload
```

## Internals

CrossPoint Reader is pretty aggressive about caching data down to the SD card to minimise RAM usage. The ESP32-C3 only
has ~380KB of usable RAM, so we have to be careful. A lot of the decisions made in the design of the firmware were based
on this constraint.

### EPUB caching

The first time chapters of an EPUB are loaded, they are cached to the SD card. Subsequent loads are served from the 
cache. This cache directory exists at `.crosspoint` on the SD card. The structure is as follows:


```
.crosspoint/
├── epub_12471232/       # Each EPUB is cached to a subdirectory named `epub_<hash>`
│   ├── progress.bin     # Stores reading progress (chapter, page, etc.)
│   ├── 0/               # Each chapter is stored in a subdirectory named by its index (based on the spine order)
│   │   ├── section.bin  # Section metadata (page count)
│   │   ├── page_0.bin   # Each page is stored in a separate file, it
│   │   ├── page_1.bin   #   contains the position (x, y) and text for each word
│   │   └── ...
│   ├── 1/
│   │   ├── section.bin
│   │   ├── page_0.bin
│   │   ├── page_1.bin
│   │   └── ...
│   └── ...
│
└── epub_189013891/
```

Deleting the `.crosspoint` directory will clear the cache. 

Due the way it's currently implemented, the cache is not automatically cleared when the EPUB is deleted and moving an 
EPUB file will reset the reading progress.

## Contributing

Contributions are very welcome!

### To submit a contribution:

1. Fork the repo
2. Create a branch (`feature/dithering-improvement`)
3. Make changes
4. Submit a PR

---

CrossPoint Reader is **not affiliated with Xteink or any manufacturer of the X4 hardware**.

Huge shoutout to [**diy-esp32-epub-reader** by atomic14](https://github.com/atomic14/diy-esp32-epub-reader), which was a project I took a lot of inspiration from as I
was making CrossPoint.
