ESP32-S3-RLCD-4.2 projects

Two firmwares for one board: a Game Boy emulator and Chrome's offline dino game, both drawn on the same 4.2" reflective LCD.

Project	What it is	Built with
gameboy_rlcd/	A Game Boy that runs from ROMs on the SD card, with a Bluetooth gamepad, save states and a WiFi ROM manager.	ESP-IDF 5.5
dino_rlcd/	The T-Rex runner, ported from Chromium's own artwork and constants.	arduino-cli

Neither uses a backlight or colour: the panel is reflective and one bit per pixel, so everything is drawn in four ordered-dither shades of ink on paper. The Game Boy emulator is the larger of the two and the one still being worked on; the dino port is finished, and both are documented and measured on real hardware rather than on a simulator.

The board

Waveshare ESP32-S3-RLCD-4.2 — an ESP32-S3-WROOM-1-N16R8 (16 MB flash, 8 MB OPI PSRAM, Bluetooth 5 LE only, no classic Bluetooth) with a 300×400 ST7305 panel, a microSD slot, an ES8311 codec and two buttons.

Function	Pins
RLCD (SPI2)	SCLK 11, MOSI 12, CS 40, DC 5, RST 41
TF card (SDMMC, 1-bit)	CLK 38, CMD 21, D0 39
ES8311 codec	I2S MCLK 16, BCLK 9, WS 45, DOUT 10; I2C SDA 13, SCL 14; PA 46
Buttons	KEY = GPIO18, BOOT = GPIO0, active low
Battery	ADC1 channel 3 = GPIO4, behind a 100k/200k divider

Sound needs a speaker on the MX1.25 2-pin connector; without one the codec still initialises and runs silently. The panel's driver came from Waveshare's own ESP32-S3-RLCD-4.2 reference, as did the pin map above.

One board, one firmware at a time

Flashing one of these replaces the other. They need different partition tables: the dino game is an Arduino sketch built with PartitionScheme=app3M_fat9M_16MB, while the emulator defines its own partitions.csv — two 2 MB application slots plus otadata, so it can carry the ROM manager in the second slot and switch between them. The two layouts put the application in different places, so the second one flashed is the one that boots, and switching means re-flashing.

The SD card is untouched by all of this. ROMs, saves and the emulator's config live on the card, not in flash, so they survive re-flashing either firmware.

Layout

.
├── gameboy_rlcd/         the emulator: ESP-IDF project
│   ├── main/             front end, menus, panel driver, input, audio, console
│   ├── manager/          the WiFi ROM manager, a second application
│   ├── components/       vendored codec_board + esp_codec_dev
│   ├── tools/            flash both apps, CJK font generator, WiFi QR, BLE scan
│   └── test/             host-side test for the HID report descriptor parser
└── dino_rlcd/            the dino game: Arduino sketch
    ├── dino_rlcd.ino     setup/loop, 60 Hz pacing, buttons, serial console
    └── src/ExternLib/    vendored codec_board + esp_codec_dev

Each project vendors its own copy of Waveshare's codec_board and Espressif's esp_codec_dev, adapted to its own build system — an Arduino sketch and an ESP-IDF component do not want the same build files. There is no shared source between the two.

Building

The two use different toolchains and neither build touches the other.

The emulator needs ESP-IDF 5.5 and the Xtensa toolchain:

. ~/esp/esp-idf/export.sh
cd gameboy_rlcd
idf.py set-target esp32s3
idf.py -p /dev/cu.usbmodemXXXX flash monitor

Both of its applications are built and flashed by gameboy_rlcd/tools/flash_all.sh, which is what you want unless you enjoy re-flashing the emulator by hand after the manager's own idf.py flash has overwritten it.

The dino game needs arduino-cli with esp32:esp32 ≥ 3.3.0 and the U8g2 library:

arduino-cli lib install U8g2
arduino-cli compile --fqbn "$FQBN" dino_rlcd
arduino-cli upload  -p /dev/cu.usbmodem1401 --fqbn "$FQBN" dino_rlcd

$FQBN is spelled out in dino_rlcd/README.md.

Both are flashed over the board's native USB-C port, which is also the serial console for each. Both open at 115200 baud.

Provenance

• Game Boy core — PaperBoy's build of Peanut-GB, vendored unmodified, with PaperBoy's menus adapted to this panel. Peanut-GB © Mahyar Koshkouei, MIT; PaperBoy © Wenting Zhang. Pinned at e70b293.
• Dino artwork and gameplay — Chromium's, extracted pixel-for-pixel from its sprite sheet and ported rule by rule from its TypeScript. Nothing is redrawn.
• Panel driver and codec glue — ported from Waveshare's reference driver and their codec_board, MIT.

Two things the emulator does not do, in case they are what you came for: CGB colour is not emulated (the hardware is, the palettes are not, so colour games are drawn as four shades), and there is no link cable. The emulator's README has the details.