526c8a5e7a
## Summary Fixes #1263 I spent half of my day(-off) reverse engineering the stock english firmware V3.1.1, it's more or less like solving a sudoku with some known pieces (like debug strings, known static addresses, known compiled function, etc) and then the task is to guess the rest. Long story short, this is the sleep routine that they use: <img width="674" height="604" alt="image" src="https://github.com/user-attachments/assets/6d53ce44-7bae-40c7-b4fb-24f898dbcc05" /> From the code above: - They pull down GPIO13 (value = 0xd) before sleep - They verify that power button is released by doing a delay loop of 50ms, similar to what we're doing - `esp_sleep_config_gpio_isolate` is called but I'm not 100% sure why - Pull up power button, note that it's likely redundant because power button should already pulled up by `InputManager` - `param1` and `param2` means enabling front/side buttons for wake up, but it doesn't used in the code in reality. But I think it's physically impossible, see the explanation below - `param3` means "wake up from power button" - `esp_sleep_start` is used; there is a logic to handle if it fails to sleep, then retry recursively (no idea why!) My observation is that they use GPIO13 so that it will be on HIGH state when the chip is powered on, without any user space code to keep it on that state. And once going to deep sleep, it goes into FLOATING by default. That may explain why it need to be in LOW state before going to sleep. (Nice trick btw) Looking again at the circuit diagram provided [here](https://github.com/sunwoods/Xteink-X4/blob/main/readme-img/sch.jpg) (note: it's not official): <img width="705" height="384" alt="image" src="https://github.com/user-attachments/assets/b98d59fd-47ca-4d3d-a24a-94bf999e957b" /> It kinda make sense as the GPIO13 and VBUS (USB VCC) have the same role, they are part of a simple "battery protection" cirtuit Now, we may wonder, how the device wake up when there is no battery at all? <img width="440" height="323" alt="image" src="https://github.com/user-attachments/assets/2981c411-239b-49a7-b9f7-9a75b6c1b6d3" /> It seems like power button is not just a simple switch between GPIO3 and ground, but it also linked the POWER_CTRL, which leads to nowhere on the diagram, but I suppose it connects the battery back for a short amount of time, just enough for the MCU to wake up, and GPIO13 goes HIGH again. It may also explain why power button becomes non-responsive for ~1 second after power on, as it's being pulled up by the current from battery (remind: high = not pressed, low = pressed) To test the theory above, I simply **comment out** the `esp_deep_sleep_enable_gpio_wakeup`: - On battery, power button works as nothing happen - On USB, it doesn't wake up, I need to press RST --- Important things about my analysis: 1. I had to name every function on the code above **manually**, but I'm 99% confident about it. The only function that I'm not sure is `esp_wifi_bt_power_domain_off` ; Edit: it was indeed mislabeled, see https://github.com/crosspoint-reader/crosspoint-reader/pull/1298#discussion_r2879670852 2. Some logic inside the stock firmware looks very strange, there is almost no mention to "arduino" in the hardware, suggesting that they may just call esp-idf functions directly, bypassing the arduino abstraction. --- ### AI Usage While CrossPoint doesn't have restrictions on AI tools in contributing, please be transparent about their usage as it helps set the right context for reviewers. Did you use AI tools to help write this code? **NO** --------- Co-authored-by: Zach Nelson <zach@zdnelson.com>
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.
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 & Usage
- EPUB parsing and rendering (EPUB 2 and EPUB 3)
- Image support within EPUB
- Saved reading position
- File explorer with file picker
- Basic EPUB picker from root directory
- Support nested folders
- EPUB picker with cover art
- Custom sleep screen
- Cover sleep screen
- Wifi book upload
- Wifi OTA updates
- KOReader Sync integration for cross-device reading progress
- Configurable font, layout, and display options
- User provided fonts
- Full UTF support
- Screen rotation
Multi-language support: Read EPUBs in various languages, including English, Spanish, French, German, Italian, Portuguese, Russian, Ukrainian, Polish, Swedish, Norwegian, and more.
See the user guide for instructions on operating CrossPoint, including the KOReader Sync quick setup.
For more details about the scope of the project, see the SCOPE.md document.
Installing
Web (latest firmware)
- Connect your Xteink X4 to your computer via USB-C and wake/unlock the device
- 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)
- Connect your Xteink X4 to your computer via USB-C
- Download the
firmware.binfile from the release of your choice via the releases page - 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 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/crosspoint-reader/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.
pio run --target upload
Debugging
After flashing the new features, it’s recommended to capture detailed logs from the serial port.
First, make sure all required Python packages are installed:
python3 -m pip install pyserial colorama matplotlib
after that run the script:
# For Linux
# This was tested on Debian and should work on most Linux systems.
python3 scripts/debugging_monitor.py
# For macOS
python3 scripts/debugging_monitor.py /dev/cu.usbmodem2101
Minor adjustments may be required for Windows.
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.
Data caching
The first time chapters of a book 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.)
│ ├── cover.bmp # Book cover image (once generated)
│ ├── book.bin # Book metadata (title, author, spine, table of contents, etc.)
│ └── sections/ # All chapter data is stored in the sections subdirectory
│ ├── 0.bin # Chapter data (screen count, all text layout info, etc.)
│ ├── 1.bin # files are named by their index in the spine
│ └── ...
│
└── epub_189013891/
Deleting the .crosspoint directory will clear the entire cache.
Due the way it's currently implemented, the cache is not automatically cleared when a book is deleted and moving a book file will use a new cache directory, resetting the reading progress.
For more details on the internal file structures, see the file formats document.
Contributing
Contributions are very welcome!
If you are new to the codebase, start with the contributing docs.
If you're looking for a way to help out, take a look at the ideas discussion board. If there's something there you'd like to work on, leave a comment so that we can avoid duplicated effort.
Everyone here is a volunteer, so please be respectful and patient. For more details on our goverance and community principles, please see GOVERNANCE.md.
To submit a contribution:
- Fork the repo
- Create a branch (
feature/dithering-improvement) - Make changes
- 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, which was a project I took a lot of inspiration from as I was making CrossPoint.