U64 BBC BASIC puts the BBC Micro's BASIC on a Commodore 64 with an Ultimate. The interpreter is the original BBC BASIC 3.10, unchanged and checked byte for byte against the reference ROM; around it is a new BBC-style MOS written for the C64 and the Ultimate. It runs at the Ultimate's turbo speed, about 30 times a BBC Micro.

What it adds: the BBC's screen modes (on 64 MHz machines with square pixels, as on a BBC), teletext MODE 7, Upic full pictures, 32 multiplexed sprites with a sprite editor, CharPad maps and a PETSCII mode; SOUND and ENVELOPE on 8 SIDs with 24 voices, a song tracker, Ultimate Audio samples and MOD music; the Ultimate's drives, a 15 MB RAM disk in the REU and a file browser; TCP, UDP, HTTP and JSON from BASIC; a BBC line editor and *HELP for every keyword and command. A VS Code extension runs and debugs programs on the real machine. See the blog post for the story and the details, and the five videos.

Made with AI: most of the code, the tests, the documentation and the videos were written with Anthropic's Claude; the goals, the design decisions and the testing on real hardware are mine. The BBC BASIC interpreter is Sophie Wilson's original, unchanged.

Requirements

• Ultimate 64, Ultimate 64 Elite or Elite II with firmware 3.15a or newer
• Commodore 64 Ultimate: not fully functional yet -- it relies on features of the Ultimate 64 firmware 3.15a, which Commodore has not yet released in a C64 Ultimate firmware update
• A 16 MB REU (switched on by the cartridge's .cfg)
• The EasyFlash version (u64bbc-ef.crt) also runs in VICE, without Ultimate Audio

Installation

1. Unzip u64-bbcbasic-1.0.0.zip and copy its folder u64bbcbasic into the folder idi8b on an SD card or USB drive of the Ultimate (make idi8b if needed), for example /SD/idi8b/u64bbcbasic/. The demos' paths assume this place.
2. In the Ultimate's file browser, start u64bbc-tmb.crt. The .cfg next to it switches on the Command Interface, the REU, Ultimate Audio, the turbo registers and 8 UltiSIDs, for this session only.
3. Try the showcase: *DIR /SD/idi8b/u64bbcbasic/demos/showcase and CHAIN "SHOW", or press F1 on an empty line and pick a program in the file browser.

The ZIP also holds the user manual as PDF (also on its own here: U64_BBC_BASIC_MANUAL-1.0.0.pdf), the demos as source and INSTALL.txt. The VS Code extension is u64-bbcbasic-1.0.0.vsix (Extensions view, ..., Install from VSIX...).

Credits

BBC BASIC by Sophie Wilson and Acorn Computers; the annotated source by Ivo van Poorten, after J.G. Harston's reconstruction; the MOD player after ModPlayer_16k by Freshness; Upic by Aleksi Eeben and Christian Gleissner; graphics programs by Eric Schraf and Aurel Wizzard. What is covered by which licence: NOTICE.md.