m4k3r-org / tinybasic

My arduino basic interpreter

Stefan's Tinybasic

The idea

My attempt to create a small basic interpreter from scratch using frugal programming techniques and minimal memory. The project was inspired by Steve Wozniak's statement that the Apple 1 basic interpreter was the biggest challenge in his professional life. Bill Gates also had started his career and hir fortune by writing a basic interpreter for the Altair microcomputer.

The program is written in C but only putchar and getchar are used from the libraries. All other code is done by hand. The C stack is not used for arithmetic to keep it minimal. The interpreter uses a set of global variables, an own stack and a static memory and variable array to emulate the low memory environment of the early microcomputers.

Arithmetic is 16 bit. The full set of logical expresssions with NOT, AND, OR is implemented C style. Conditions are part of the arithemtic and not separate like in many basic dialects. This makes the call stack of the recursive descent deeper but simplifies other code. To reduce the memory footprint of this part of the runtime code no arguments are passed in the C functions. Instead, an own multi purpose 16 bit stack is added.

Memory access is strictly 16bit and 8bit. For memory, stack and variable access, array logic is used and not C pointers. This allows all pointers to be short integers which can be stored on the arithmetic stack if needed.

The interpreted can be compliled with standard gcc on almost any architecture or in the Arduino IDE without changes.

Look at the WIKI https://github.com/slviajero/tinybasic/wiki for more information.

See also:

• https://en.wikipedia.org/wiki/Recursive_descent_parser
• https://rosettacode.org/wiki/BNF_Grammar
• https://en.wikipedia.org/wiki/Tiny_BASIC
• https://github.com/slviajero/tinybasic/wiki/Unforgotten---Dr.-Wang's-BASIC
• https://github.com/slviajero/tinybasic/wiki/The-original-Apple-1-BASIC-manual

Language features in a nutshell

The intepreter is compatible with two of the 1976 early basic dialects. It implements the full language set of Dr. Wang's Palo Alto Tinybasic from the December 1976 edition of Dr. Dobbs (https://github.com/slviajero/tinybasic/wiki/Unforgotten---Dr.-Wang's-BASIC). This is a remarkably complete little language with many useful features.

The interpreter also implements the specification of Apple Integer BASIC sold for the Apple 1 computer (https://github.com/slviajero/tinybasic/wiki/The-original-Apple-1-BASIC-manual). It should be fully Apple 1 compatible.

I have never worked with a computer running any of the two BASIC dialects. All the implementation has been done from the manuals cited above.

A few things have been added by myself. As the main target hardware is Arduino microcontrollers, I added EEPROM access, EEPROM program storage and autorun, control of digital and analog I/O as well as the delay function.

For further information, please look at: https://github.com/slviajero/tinybasic/wiki

Files in this archive

basic.c is the program source. It can be compiled directly with gcc. No header is needed or supplied.

TinybasicArduino/TinybasicArduino.ino is an exact copy of basic.c, nothing needs to be added or adapted.

monitor.py is a little serial monitor to interact with the running BASIC interpreter on the Arduino. It allows very simple loading of files into the Arduino and saving of output to a file on a computer. arduinoterm is a wrapper of monitor.py.

The various programs with the extension .bas are test files for the interpreter.