GFX-Basic for the rp6502 PicoComputer

GFX-Basic is an enhanced version of EhBASIC for the rp6502 PicoComputer, adding graphics, sound, and improved file handling while staying within classic 8-bit constraints.

For a complete list of commands and syntax, see COMMANDS.md.

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A Brief History

Having grown up in the era of 8-bit home computing—and after years of building various electronic kits—the PicoComputer immediately caught my interest. I ordered the circuit board and components, assembled it in about two hours, and brought it to life. After loading the .uf2 files along with the BASIC and terminal ROMs, I spent some time exploring what it could do.

The terminal program was a lot of fun, especially connecting to modern retro BBSes. BASIC, while enjoyable, felt a bit limited in places. Then I came across a video about coding on the PicoComputer with AI and thought:

“Why not see what ChatGPT can do with EhBASIC?”

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From Simple Idea to Full Expansion

My original goal was modest: add a CLS command and improve some text formatting.

Two weeks later, the project had grown far beyond that.

Together, ChatGPT and I expanded EhBASIC to include:

• CLS — Clear screen
• CLG — Graphics mode select
• PLOT — Plot a pixel
• LINE — Draw lines
• BOX — Draw rectangles
• CIRCLE — Draw circles
• SOUND — Generate tones (with NOTEON/NOTEOFF for lower-level control)

What started as a small enhancement became the foundation of a full graphics command set.

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Development Experience

My programming background is primarily in BASIC, with only limited experience in C++. Working with AI and tools like VS Code turned out to be both enjoyable and surprisingly productive.

More than once, I thought the project was finished—only to return a day later with another idea:

“Wait a minute… we need to add…”

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Expanding Further

As development continued, the project gained:

• Graphics support
• Sound support
• File handling
• Directory management

Commands added:

• DIR — Directory listing and drive selection
• MKDIR — Create directories
• CHDIR — Change directories

Additional commands and functions include:

• NOTEON / NOTEOFF — Low-level sound control
• LOCATE — Position the text cursor
• COLOR — Set text and background colors (text mode only)
• EOF() — End-of-file detection for file handling
• TI — Monotonic 100 Hz system timer
• TI$ — Realtime clock string in HHMMSS UTC format

TI returns a continuously increasing timer value based on the PicoComputer system clock.

TI$ returns the current realtime clock time as a six-character string:

PRINT TI$

Example output:

153138

Which represents:

15:31:38 UTC

Notes:

• TI$ always returns UTC time, not local timezone time.
• Programs requiring local time should apply their own timezone offset.
• LEN(TI$) always returns 6.
• TI$ is inspired by Commodore BASIC but implemented specifically for the RP6502 PicoComputer environment.

See COMMANDS.md for full details and syntax.

At this point, the system felt nearly complete.

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The One That Got Away: RMDIR

There was just one command left to add:

• RMDIR — Remove directory

This is where reality set in.

To support all features, available RAM for BASIC had already been reduced from 52 KB to ~37 KB—roughly comparable to a Commodore 64.

Rather than reduce memory further, development stopped here.

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Final Notes

GFX-Basic is:

• Feature-rich
• Compact
• Built within authentic 8-bit-style constraints

While you can create and navigate directories with:

• MKDIR
• CHDIR

Removing directories must be done via:

• The system monitor
• Another computer

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Documentation

For detailed command syntax and usage, see:

• COMMANDS.md

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Closing Thoughts

GFX-Basic reflects both modern experimentation and classic limitations—a blend of AI-assisted development and retro computing philosophy.

And honestly… that feels exactly right.

Development Environment

This repository includes a .vscode configuration inherited from and compatible with the RP6502/EhBASIC PicoComputer development workflow.