memxFORTH-init

A minimal Forth-like core for AVR (ATmega328P), designed to experiment with unified RAM and FLASH word handling using __memx pointers in C. This project serves as a proof of concept and debugging tool base. Based on https://arduino.stackexchange.com/questions/97384/how-to-manage-mixed-pointers-to-ram-and-progmem-on-arduino

Project Goals

• Unified handling of dictionary words in both RAM and FLASH
• Explore low-footprint interpreter design in C
• Use __memx for flexible word list chaining and execution
• Minimal working example, not a full Forth implementation

Current Features

• Dictionary traversal using __memx pointers
• Execution of basic hardcoded words in FLASH and RAM
• Modular, small codebase suitable for embedded hardware debugging
• Uses C and AVR-GCC (also Arduino IDE compatible)

Build

Compile as usual with avr-gcc, tested on ATmega328P.

Arduino IDE:

• Open memxFORTH-init.ino
• Select "Arduino Nano" with ATmega328P
• Upload as usual

Usage

• Developed for ANSI terminal on a wide monitor
• Serial speed: 115200 baud
• Colors can be disabled in colors.h
• After upload, the demo:
  • Prints a header from the Arduino .ino
  • Builds the word WORDS in RAM
  • Prints memory debug dumps (green marks current position)
  • Pushes 0x21 to the data stack
  • Prints word list
  • Runs the word TEST (defined as : TEST DOUBLE DEBUG ;)
  • Note: press a key on each NEXT to continue
  • Traverses definitions (: DOUBLE DUP + ;) and computes the result
  • Uses a hacked DEBUG word to return to main code and end the demo
  • Pops and displays result from stack - see Notes
• Intended to verify whether __memx pointers can be used for seamless access to both FLASH and RAM word dictionaries
• RAM usage:
  • 3 variables
  • 10-item data stack
  • 10-item return stack
  • 100 bytes for user-defined words
  • Everything else resides in FLASH
• This project is mainly a source reference for other tools

Notes

This is not meant to be a complete Forth interpreter. It is a technical foundation for later interactive tools, such as hardware pin testing, control, and diagnostics.

Fun detail:

I threw 0x21 at my FORTH together with the word : DOUBLE DUP + ;

and it left 0x42 on the stack - I’ll take that as a hexadecimal answer. :)

License

GPL 2 or GPL 3 - choose the one that suits your needs.

Author

Gilhad - 2025