Dragon BASIC

Introduction

This is an open-source recreation of Dragon BASIC, a BASIC software development kit for the Game Boy Advance written by Jeff Massung.

It consists of a BASIC compiler reconstructed from the last released binary, and a completely rewritten compiler backend and libraries. All the while it remains (almost) fully compatible with legacy Dragon BASIC 1.4.x.

The system produces smaller and much faster code thanks to the following improvements:

MF

• uses literal pools instead of accessor functions
• generates Thumb instead of ARM code (all library functions have also been rewritten in Thumb)
• supports functions (both assembler and TIN) in IWRAM
• supports "naked" words that omit the prolog, reducing function call overhead
• supports inlining of TIN words
• optimizes many common TIN word sequences into more efficient machine code
• optimizes many operations on constants
• uses inlined comparisons and conditional branches
• runtime helper functions have been eliminated entirely

DBC

• produces more easily optimized TIN code
• uses function arguments in place instead of copying them
• supports functions and SUBs in IWRAM
• no longer uses accessors for one-dimensional arrays

Numerous bugs have been fixed in the runtime library and the BASIC compiler, and a lot of new features have been added:

Assembler

• support for Thumb instruction set
• pseudo-instruction MOVI simplifies constant loading
• support for forward references (no more need to use #offset)

Asset handling

• support for many new image and sound formats using FreeImage and libsndfile
• support for MOD and XM music files using pimpmobile
• support for loading Mappy FMP files (supports 8x8 or 16x16 tiles and layers, as well as animations)

BASIC Language

• addition of local variables which are, incidentally, much faster than globals, so use them! (not implemented for arrays and strings)
• byte and halfword-sized DATA and READ commands
• support for a default include path; no need to state the full path anymore
• allows leading underscores in identifiers
• implemented GOTO command, making DB deserve the name "BASIC" again

Debugging

• "-sym" option creates a NO$GBA-compatible symbol file for debugging/profiling
• "-debug" option produces an assembly listing

Documentation

• addition of many tutorials and sample programs from archeological digs at the Internet Archive and living fossil web sites.
• addition of Dragon BASIC language reference and timer API documentation to CHM file (from DDLullu's fix library)
• added syntax highlighting descriptions for ConTEXT and JOE

Library

• new 32 and 8-bit peeks and pokes
• uses BIOS call to wait for vertical blank (reduces power consumption, and works better overall)
• several other blocking functions use BIOS calls to reduce power consumption
• LOADPAL256, LOADSPRITE, LOADTILES, and UPDATESPRITES now use DMA
• new SETTILEFAST and CLEARTILESFAST functions ignore rarely significant corner cases in favor of speed
• uses byte-sized or word-sized instead of halfword-sized accesses where beneficial to performance
• moved constants together with the corresponding functions to avoid having to include the entire library all the time
• rewritten string memory allocator that actually works
• new ASC() and CHR$() functions from DDLullu's fix library
• signed numbers support in STR$()
• many functions have been inlined or declared naked to improve performance
• sound playback uses DMA instead of timer interrupt, reducing CPU load
• new input functions that simplify checking for key events

Runtime Environment

• possibility to link C libraries into the TIN runtime (used to integrate pimpmobile)
• sets WAITCNT register to a sane value to improve memory access timing
• support for user DMA interrupt handlers

Oh, and there is no size limit... :)

Building

Requirements

You need:

• Some sort of C++ compiler for your host system. (MinGW should work for Windows users.)
• The FreeImage and libsndfile libraries. For Linux users, these should come with your distribution. Windows users can get them from the MSYS2 package repository.
• devkitPro to build the runtime environment.
• Free Pascal to build the documentation CHM file. (Dragon BASIC traditionally uses documentation in CHM format, and Free Pascal contains the only open-source CHM compiler that I am aware of.)

For POSIX platforms

Run make linux.

For Win32 platforms

Run make win_cross.

For my own system

Run make to build a native Linux version and a cross-compiled Win32 version.

Building the documentation

Run make doc.