FAQ

Welcome to the frequently asked questions page! Here you’ll find simple answers to the questions that come up the most in our community — about Hollyhock, programming the calculator, and what’s actually going on inside that ClassPad of yours. If you’re brand new, this is a great place to start.

What is Hollyhock?

Hollyhock (HHK) is a community-made modification (a custom firmware add-on) for the Casio ClassPad II fx-CP400. Once installed, it lets your calculator run custom programs made by the community — games, tools, Python, and much more. There are two generations today: V2 (the classic version) and V3 (the current one). Hollyhock is built by the community, so everyone plays a part in making it better.

What’s the difference between V2 and V3?

Back in the early V2 days (over 6 years ago), there was no shared compiler — everyone built their own local toolchain with custom patches, and V2 programs were simple programs compiled for one fixed memory address, a bit like burned ROM. That made programs very hard to build and port. V3 fixes this: programs are now real, standard ELF files, and the loader is dynamic and flexible, so it can support multiple OS versions — including future ones. Almost every V2 app has already been ported to V3, so V3 is the recommended version today.

What is a .hh3 file?

A .hh3 file is a small ELF executable : the standard executable format used on Linux. If you’re more familiar with Windows, think of it like a .exe file, but for your calculator. When you compile your C/C++ code, the compiler produces a .hh3 file, and the Hollyhock launcher (“YAL”) loads it and runs your program.

Can I still use V2?

Yes! Switching between V2 and V3 is just a matter of swapping the run.bin file at the root of your calculator (V2 apps still work). That said, V3 is recommended as it is actively developed, more flexible, and nearly everything has been ported to it.

Is my calculator backwards compatible between versions?

Mostly, but don’t expect perfect forward compatibility. Apps made for one setup generally keep working, but there’s no guarantee that something built today will work on a future OS or firmware version without an update. When in doubt, check the app store for the latest version of a program.

How do I update back to the official OS?

Before exams, we recommend restoring the official Casio OS so your calculator is not modified. Download the official updater from TI-Planet’s archive Mac Version, then put the calculator in normal OS update mode.

On the calculator:

1. Connect the ClassPad to your computer with a standard USB cable.
2. When the USB menu appears, press Clear or choose 5: Cancel.
3. Open the Communication app.
4. Open the top menu Link.
5. Choose OS Update, then press OK.
6. Leave the calculator alone until the update is complete. The screen will go blank, then the calculator will ask for touch screen alignment and initial setup again.

On the computer, wait 10 to 20 seconds for the USB drivers to install if needed, then click OK in the updater to start the official update. The update takes several minutes. Do not unplug the calculator while it is running.

I’m new to programming : where should I start?

The community recommendation is to start with Python, using the calculator’s Python support. It’s forgiving, interactive, and you’ll learn how the calculator works along the way. Once you’re comfortable, moving to C/C++ is natural as most of what you learned in Python still applies. A great entry point is the Python app and the Python section of this wiki.

What are the ways to make native programs?

There are basically two ways to create native programs, and both produce .hh3 files that look identical to the user:

1. The Hollyhock native SDK — it tries to play as nicely as possible with the Casio OS, so your hello world just prints on the screen as expected. This is the friendlier route.
2. The gint kernel — a custom kernel that talks directly to the hardware, ignoring most of the Casio OS. It’s the way to go if you want full control and performance: fast drawing, direct access to the LCD controller, USB, and so on. Most games are made with gint. See the gint getting started guide.

It’s mostly a matter of which template you start from — the template guides your code quite a lot.

Which compiler does the calculator use?

The Hollyhock native SDK uses a recent GCC toolchain that even supports modern C++, which is quite impressive for an embedded toolchain. The gint toolchain uses a slightly older GCC with custom patches. That’s also why we all prefer to use the same compiler — shared toolchains make troubleshooting much easier, and the two toolchains are not interchangeable.

What CPU is inside the ClassPad?

The fx-CP400 is powered by a Hitachi (now Renesas) SuperH SH4A-DSP — the same CPU family that powered the Sega Dreamcast, so we share a passion with the Dreamcast homebrew scene. The SuperH is a simple, well-designed Japanese architecture (you could call it the “grandma of ARM”). Because it’s an SoC (a single chip doing CPU, audio DSP, battery measurement and more) with almost no modern features, it’s actually a wonderful chip to learn CPU basics hands-on — things other platforms make deliberately hard to touch.

Does it have an FPU?

No — unlike the Dreamcast’s SH4, the CP400’s CPU has no floating-point unit (FPU), the small extra circuit that computes decimal numbers like 3.14 very fast in hardware. Floating-point math is emulated in software, which is slower. Fun fact: in the 90s most CPUs had no FPU either — it’s the modern ones that are the exception! This limitation is exactly why the DSP and audio side of the chip is such an interesting thing to explore.

How much RAM does it have?

The ClassPad has around 16 MB of RAM — an enormous amount for a calculator — but it’s split into several regions with different personalities: a small but very fast RAM intended for the DSP (audio), and larger but slower RAM for general use. There’s also no MMU (see the next question), so no virtual memory. Exploring the address space and learning which region is good for what is a fun part of ClassPad hacking.

Why can’t programs load anywhere in memory like on a PC?

Because the ClassPad has no MMU and no dynamic linker. On a modern system like Linux, the dynamic linker loads programs and libraries at whatever position is free and fixes everything on the fly; the MMU also gives each program its own “virtual” memory so it believes it’s alone. On the ClassPad, code is compiled for fixed load addresses — if you load it somewhere else, all the addresses inside are wrong. The classic workaround is an interpreter: something like Python is essentially the “stub” you described — it reads bytecode from anywhere and executes it, just more slowly than native code.

How does the screen work?

Two ways! You can either write pixels into a buffer — a large region of memory that gets mirrored to the screen — or talk directly to the LCD controller by sending commands to a memory address. The panel is partially MIPI, so a few basic commands (put pixel, refresh…) exist at the hardware level. Drawing directly to the LCD controller is the fastest route, and it’s one of the things gint makes easy.

How fast is the CPU? Can I overclock it?

The CPU runs at around 100 MHz and can be overclocked — tools like CPtune exist for that. In practice, keep it modest: the touchscreen stops responding when input polling goes above roughly 50 MHz (it’s related to the I2C bus used by the touch controller), and memory limits (CL3 vs CL2 timings) also come into play. Don’t expect magic either — overclocking mostly makes the UI feel snappier, not necessarily your calculations.

Can I compile on Linux?

Yes, absolutely! Both toolchains ship as Docker images, so you don’t need Windows at all:

• Hollyhock native SDK: ghcr.io/classpaddev/hollyhock-3
• gint: ghcr.io/therainbowphoenix/gint-docker

And if you want a zero-setup option, the templates work in GitHub Codespaces — you get a ready-to-code environment in your browser without installing anything.

Is there a compiler that runs on the calculator itself?

Nothing concrete yet. The flash is small and C compilers are hungry, which makes self-hosting very difficult — though there have been projects trying to bring TCC (a tiny C compiler) to the calculator. For now, you’ll compile on your computer (or in Codespaces) and copy the .hh3 file over.

Where can I get help?

The best place is our Discord community: discord.gg/knpcNJTzpd. Hollyhock and the whole ClassPad development scene are community projects — the people writing the firmware, the SDKs and this wiki hang out there, and questions from beginners are always welcome. No question is too basic; we’ve all been there.

Still stuck?

If your question isn’t answered here, come join our Discord and ask! The community is friendly, and someone has almost certainly hit the same problem before. And hey — the calculator will make you much, much better at computers.