ESP32 Platform Details

The ESP32 is the heart of every FujiNet device. This page documents the specific ESP32 modules, configurations, and capabilities used across the FujiNet ecosystem.

ESP32-WROVER Module

FujiNet exclusively uses the ESP32-WROVER module variant. The WROVER provides significantly more RAM and Flash than the WROOM variant, which is required for FujiNet’s firmware to function correctly.

Important: Do not use ESP32-WROOM modules with FujiNet. The reduced memory will cause firmware instability and failures.

WROVER vs WROOM Comparison

Module Specifications

GPIO Pinout

The ESP32 provides a rich set of GPIO pins used by FujiNet for bus communication, SD card access, LEDs, buttons, and other peripherals. The exact pin assignments vary by platform.

Atari 8-Bit GPIO Assignments

graph LR
    subgraph ESP32 GPIO
        direction TB
        SIO_CMD[GPIO - SIO Command]
        SIO_DI[GPIO - SIO Data In]
        SIO_DO[GPIO - SIO Data Out]
        SIO_CLK[GPIO - SIO Clock]
        SIO_MTR[GPIO - SIO Motor]
        SIO_PROC[GPIO - SIO Proceed]
        SIO_IRQ[GPIO - SIO Interrupt]
        SD_CS[GPIO - SD CS]
        SD_MOSI[GPIO - SD MOSI]
        SD_MISO[GPIO - SD MISO]
        SD_CLK[GPIO - SD CLK]
        SD_DET[GPIO 15 - SD Detect]
        LED1[GPIO - WiFi LED]
        LED2[GPIO - BT LED]
        LED3[GPIO - SIO LED]
        BTN_A[GPIO - Button A]
        BTN_B[GPIO - Button B]
    end

Key Pin Functions

SIO Bus Interface (Atari)

On v1.3 and later boards, SIO lines pass through two 74LS07 open-collector buffer ICs. P-channel and N-channel transistors disconnect the buffers when FujiNet is powered off, electrically isolating the ESP32 from the Atari bus.

Memory Layout

The ESP32-WROVER’s memory is used by FujiNet firmware as follows:

graph TD
    subgraph "ESP32-WROVER Memory Map"
        direction TB
        A["Internal SRAM (520 KB)<br/>Firmware heap, stack, variables"]
        B["External PSRAM (8 MB)<br/>Disk image buffers, network buffers,<br/>large data structures"]
        C["Flash (16 MB)<br/>Firmware partitions, SPIFFS,<br/>NVS, OTA update slots"]
    end
    A --- B --- C

Flash Partition Layout

PSRAM Usage

The 8 MB of external PSRAM is critical for FujiNet operations:

• Disk image buffering – caching sectors from SD card or network sources
• Network buffers – HTTP response bodies, TNFS data
• Printer output – PDF generation buffers
• Protocol adapters – translation buffers for platform-specific protocols

WiFi Capabilities

WiFi Operating Modes

1. SoftAP Mode – On first boot or after config reset, FujiNet creates its own access point for initial setup
2. Station Mode – Normal operation, connecting to a user’s WiFi network
3. Concurrent Mode – Both AP and Station can run simultaneously during configuration

External Antenna

Starting with hardware v1.6, FujiNet supports an external antenna option. This requires:

• A U.FL/IPEX connector on the ESP32-WROVER module
• Correct resistor placement on the module to route the RF signal to the external connector
• A compatible 2.4 GHz antenna
• The external antenna case design (available in the hardware repository)

ESP32-S3 for RS-232

The next-generation FujiNet architecture uses the ESP32-S3 variant for RS-232-based platforms. This is part of the universal FujiNet design that pairs an ESP32 (or host computer) with an RP2040 or RP2350 ARM processor as the physical bus interface.

ESP32-S3 Advantages

RS-232 Architecture

In the RS-232 design, the system is split between two processors:

graph LR
    A[Legacy Computer] -->|RS-232| B[RP2040/RP2350<br/>Bus Interface]
    B -->|Serial / SPI| C[ESP32-S3<br/>Device Emulation<br/>+ Network]
    C -->|WiFi| D[Internet]
    C -->|USB| E[Host Computer<br/>Optional]

The RP2040/RP2350 handles the physical bus timing and protocol requirements, while the ESP32-S3 (or a host computer running FujiNet-PC) manages device emulation, network communication, and the web interface. This separation allows the bus interface to meet strict timing requirements independently of the higher-level application logic.

Development Board

For platform development, FujiNet uses the ESP32-DevKitC-VE, which provides:

• ESP32-WROVER-E module
• USB-to-UART bridge (CP2102 or similar)
• Boot and Reset buttons
• Breadboard-compatible pin headers
• 3.3V and 5V power rails

See the Board Bring-Up page for instructions on setting up a DevKit for new platform development.