c64-ultimate

Programming the C64 and C64 Ultimate from modern tools: BASIC, cc65 C, Python servers, and SwiftLink-style TCP/HTTP over the Ultimate’s emulated modem.

What works today (C64 Ultimate)

Approach	Where	Verified
BASIC + SwiftDriver	c64u-kernal/ on kernal.d64	SIMPLE, SIMPLE-WOTD, HTTP-GET, WORD-SEARCH
Pure C (no driver file)	httpget-c/	httpget.c, wotd.c via make run
Direct ACIA BASIC	Root http-get.bas, word-search.bas	Real SwiftLink / VICE / some older C64U setups only

New C64 Ultimate firmware often hangs on root programs that poll $DE00 directly (PEEK(SR) bit 3). Use c64u-kernal/ or httpget-c/ instead.

Quick start — C64 Ultimate readers

1. Menu → ACIA mapping DE00/NMI, Hardware mode SwiftLink.
2. Build the disk: cd c64u-kernal && ./build-disk.sh
3. On the C64: LOAD"SIMPLE",8 then RUN (HTTP smoke test).
4. Then HTTP-GET, SIMPLE-WOTD, WORD-SEARCH.

Full instructions: c64u-kernal/README.md, DISK_CREATION.md.

What’s in the repo

c64u-kernal/ — KERNAL programs for C64 Ultimate

BASIC programs that LOAD "swiftdrvr" and use OPEN / PRINT# / GET# through Bo Zimmerman’s SwiftDriver. build-disk.sh produces kernal.d64 for Compute! / community distribution.

• simple.bas — minimal HTTP test (start here)
• simple-wotd.bas — raw TCP to the Python BBS
• http-get.bas — fetch and format a web page
• word-search.bas — Compute! word-search demo (works; slower at 1200 baud)
• swiftdrvr.prg — driver binary (disk name SWIFTDRVR)

httpget-c/ — single-PRG C HTTP/TCP clients

Direct 6551 ACIA access at $DE00 with an NMI ring buffer (nmi.s). No separate driver file. Deploy to the Ultimate with:

cd httpget-c && make run

Uses runner.py (HTTP POST to the Ultimate’s run_prg API). See SPEC.md for wire-protocol gotchas and architecture.

swiftdriver/ — Bo Zimmerman’s SwiftDriver (full source)

Vendored from Swiftdriver.zip: swiftdrvr.asm, LADS project, Apache License 2.0. See swiftdriver/PROVENANCE.md.

Python BBS (bbs.py, wotd.py, funct.py)

PETSCII BBS server for C64 clients over TCP (port 6464). Used by SIMPLE-WOTD and wotd.bas. Based on jalbarracinv/python-cbm-petscii-bbs.

pip install requests
python3 bbs.py

Root BASIC programs (direct ACIA)

http-get.bas, word-search.bas, wotd.bas, swiftlink.bas — direct PEEK/POKE at $DE00, often at 38400 baud. Fine on hardware SwiftLink or VICE; not the first choice on new C64 Ultimate firmware.

http-get-kernal.bas duplicates the KERNAL approach at repo root (canonical copies live in c64u-kernal/).

Other

• httpget-tool/ — planned BASIC-callable resident HTTP tool (REU storage); scaffold only
• swiftdriver-c/ — educational C port of SwiftDriver
• multiplex.c-c64/ — sprite multiplexing demo (separate from HTTP work)
• runner.py, rbas.sh — tokenize BASIC with petcat, POST PRG to C64 Ultimate

C64 Ultimate: programs freeze while connecting?

Symptoms: “connecting…” then hang, or host-side timeout with no data.

1. Confirm menu: ACIA DE00/NMI, SwiftLink mode.
2. Use kernal.d64 from c64u-kernal/, not root direct-ACIA programs.
3. Disable JiffyDOS for KERNAL/SwiftDriver programs.
4. Full power cycle after modem errors (reset alone may not clear the emulated modem).

Deploy a single program to the Ultimate (no disk)

Requirements: petcat (VICE), requests, python-dotenv, .env with C64U_PASSWORD.

./rbas.sh c64u-kernal/simple.bas

Or for C:

cd httpget-c && make run

runner.py POSTs to http://<your-ultimate>/v1/runners:run_prg.

Remote hosts (demos)

Service	Host	Port
HTTP demos	php.retrogamecoders.com	80
BBS / WOTD	bbs.retrogamecoders.com	6464

Project documentation

Doc	Contents
SPEC.md	Architecture, gotchas, roadmap
c64u-kernal/README.md	KERNAL programs, baud table, credits
DISK_CREATION.md	Building kernal.d64

Licenses

• This repo’s own code (BASIC, Python, C except vendored driver) — LICENSE
• SwiftDriver (swiftdriver/) — Apache License 2.0, Bo Zimmerman — swiftdriver/LICENSE