GXU 1

A custom GPU co processor built on an ESP32 S3 microcontroller, a handful of resistors, and about two days of work. It drives a real VGA monitor, executes a custom binary instruction set over WiFi, and streams live telemetry back to a React dashboard. Total component cost: under 700 rupees.

what it actually is

GXU 1 stands for Graphics Execution Unit, Revision 1. The idea was simple: can you build something that genuinely deserves to be called a GPU without using any dedicated display hardware? No display controller IC, no FPGA, no HDMI driver chip. Just a microcontroller, some resistors, and some decisions.

The answer turned out to be yes. GXU 1 accepts drawing commands over WebSocket, decodes them against a defined binary ISA, rasterizes them into a framebuffer using actual algorithms like Bresenham, and streams the result to a VGA monitor at 320x240 at 60Hz using a handbuilt R-2R resistor ladder DAC. The whole thing runs on two FreeRTOS cores with a hard architectural split: Core 0 handles all network traffic, Core 1 handles all rendering. They communicate through a FreeRTOS queue. DMA handles the display output independently of both.

the ISA

GXU-1 has 8 opcodes. Every command is a binary packet with a one-byte opcode followed by arguments encoded as 16-bit big-endian integers.

opcode	mnemonic	what it does
0x01	GXU_CLEAR	fill entire VRAM with a color
0x02	GXU_PIXEL	set one pixel
0x03	GXU_LINE	Bresenham line between two points
0x04	GXU_RECT_FILL	filled rectangle
0x05	GXU_RECT_OUTLINE	hollow rectangle
0x06	GXU_BLIT	copy a VRAM region to another location
0x07	GXU_TEXT	render ASCII string using 5x7 bitmap font
0xFF	GXU_SWAP	flip double buffer, tear-free

Color is encoded as a single byte: [B1 B0 G1 G0 R1 R0 xx xx]. Two bits per channel, 64 total colors.

A JSON equivalent of a single line command would be around 58 bytes and take several hundred microseconds to parse. The binary packet is 10 bytes and parses in under 5 microseconds.

hardware

The VGA color signal is analog, ranging from 0V to 0.7V per channel. The ESP32-S3 only outputs digital 0V or 3.3V. Bridging that gap is the R-2R resistor ladder: a chain of 270 ohm and 560 ohm resistors that converts 2 digital bits per channel into the correct analog voltage. The whole DAC costs about 35 rupees in components.

The ESP32-S3 was chosen specifically because it has a hardware LCD parallel interface. This lets the DMA controller drive all 8 GPIO pins simultaneously in sync with VGA timing, at 25 MHz, without any CPU involvement. The original ESP32 does not have this peripheral.

system architecture

flowchart TD
    A([browser / python script / any wifi device]) --> B
    subgraph net["core 0 — command processor"]
        B[wifi stack + websocket server\nport 8080]
        C[isa packet decoder\nisa_decode]
        D[telemetry json sender\nevery 200ms]
        B --> C
    end

   C -->|xQueueSend| Q[(freertos queue\ndepth 64)]
    Q -->|xQueueReceive| E

subgraph gpu["core 1 — gx core / rasterizer"]
        E[isa executor\nswitch on opcode]
        F[bresenham line\nrect fill / blit\nbitmap text]
        G[vram\n320x240 — 76800 bytes]
        H[tile heatmap\n16x12 counters]
        E --> F
        F --> G
        F --> H
    end

 G -->|dma — 25.175 mhz| I[8 gpio pins\nlcd parallel bus]
    H -->|read every 200ms| D
    D -->|websocket telemetry| A

I --> J[r-2r resistor ladder dac\n270ohm + 560ohm — 35 inr]
    J --> K([vga monitor\n320x240 at 60hz\nanalog rgb + hsync + vsync])

style net fill:#f0ece4,stroke:#c0bbb0,color:#1a1814
    style gpu fill:#ebf4f0,stroke:#aacfc4,color:#1a1814
    style Q fill:#1a1814,color:#f0ece4,stroke:#1a1814
    style K fill:#c0392b,color:#fff,stroke:#c0392b
    style A fill:#1a1814,color:#f0ece4,stroke:#1a1814

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dashboard

The React/Vite dashboard runs in a browser on any device connected to the same WiFi. It sends binary ISA packets over a persistent WebSocket connection and receives telemetry JSON from the ESP32 every 200ms. The VRAM heatmap divides the 320x240 screen into 192 tiles (16 columns by 12 rows) and shows which regions are being written most heavily, using the same tile access frequency visualization pattern as AMD's Radeon GPU Profiler.

BOM

component	cost
ESP32-S3-DevKitC-1-N8	450-500 INR
270 ohm resistors (18x)	20 INR
560 ohm resistors (9x)	10 INR
100 ohm resistors (2x)	5 INR
VGA DB-15 connector	30-50 INR
breadboard + jumper wires	100 INR
total	under 700 INR

software emulator

If you do not have the hardware, there is a full browser based emulator that implements the complete ISA in JavaScript using the Canvas API and if you also want full blown explaination then do checkout the blog below:

Blog post & Emulator check this out

running the firmware

# clone the repo
git clone https://github.com/Princess0407/GXU-1.git

# open in Arduino IDE or PlatformIO
# set your WiFi credentials in config.h
# flash to ESP32 S3-DevKitC 1 N8
# open serial monitor to get the IP address
# navigate to that IP in a browser

Dependencies: ESPAsyncWebServer, ArduinoJson, FreeRTOS (included with ESP IDF).