Dave Schmenk's Projects Page

October 20, 2013

What is the Apple II Pi?

Filed under: Apple II, Hardware, Raspberry Pi, Software — dave @ 1:10 pm

Basically, the Apple II Pi is the integration of an Apple II with a Raspberry Pi (http://www.raspberrypi.org) to create a hybrid computer combining the input devices and storage mediums of the Apple with the CPU, GPU (graphical processing unit), USB, and network capabilities of the Broadcom BCM2835 SoC (think smartphone processor).  The concept is to create an updated version of the Apple II using some imagination, low-level drivers, off-the-shelf hardware, and a closely coupled communications channel; thus bringing semi-modern hardware and 32 bit *nix software to the Apple II platform.  The Apple II is running as a dedicated I/O processor for the Raspberry Pi under ProDOS.  The Raspberry Pi is running a version of Debian Linux: Raspbian.  Much like the PC Transporter card brought MS-DOS and the Z-80 card brought CP/M, the Apple II Pi brings Linux to the Apple II using the Apple’s input devices and the Raspberry Pi’s video output.  As such, knowledge and familiarity with Linux is required to get the most out of its environment.  Under Linux, the Apple II Pi can read and write the Apple’s storage devices (floppies/harddrives/CFFA) and also run the GSport Apple IIgs emulator (http://gsport.sourceforge.net).  Together, GSport and Apple II Pi provide an immersive environment providing access to most of the Apple II hardware you own plus an accelerated ~20MHz 65816 with up to 8 MB RAM, and all the disk images you can fit on the SD card.

Videos of Apple II Pi development

Videos of Apple II Pi in action

Download the User Manual


What additional parts are needed to use the Apple II Pi adapter card?

Aside from a functional Apple II (64K with 5¼ floppy drive connected to slot 6), you need a Raspberry Pi with an installed OS on its SD card.  To attach a DVI or HDMI monitor/TV to the Raspberry Pi, an HDMI angle adapter is needed to redirect the downward facing HDMI port once the Raspberry Pi is attached to the Apple II Pi adapter card.  Depending on which slot the Apple II Pi will be plugged in to, a 90 or 270 degree adapter will be needed.  An HDMI or HDMI->DVI cable long enough to exit the Apple II case and attach to the monitor/TV is also required.  If you don’t have an Apple II mouse, a USB mouse will be required for running the X Window GUI environment.

Is a power supply needed with the Apple II Pi adapter card?

No.  The Raspberry Pi gets power from the Apple II through the adapter card’s header connection.

Is the Raspberry Pi talking directly to the Apple II peripherals?

No, the Apple II is running a custom driver that reads input from the keyboard and mouse, then sends these events over a high speed serial connection to a custom driver on the Raspberry Pi that injects them into the Linux input subsystem.  The Apple II keyboard and mouse look just like any other keyboard and mouse to the Raspberry Pi.  The Apple II joystick and storage devices are made available to Linux with additional drivers that run code on the Apple II using a special Apple II Pi protocol.

Additional information:  There was talk about interfacing the Raspberry Pi directly to the Apple II bus when this concept was originally posed on comp.sys.apple2.  However, after reviewing the I/O pins on the Raspberry Pi and the real-time software challenges of this approach, the decision to interface the two computers using a high-speed serial interface with a custom protocol and client/server drivers was made.  This method also allows the Apple IIc and Apple IIe with a Super Serial Card to use the Apple II Pi software without modification.  This is, in fact, how the software was developed before and after the Apple II Pi interface adapter was built.

Do I have to use the Apple II keyboard and mouse?

No, the Raspberry Pi has USB ports (one on the Model A, two on the Model B) that can be used to plug in modern keyboards and mice.  Additional devices can be plugged in using a compatible USB hub.  They can be used in parallel with the Apple II keyboard and mouse.  If you don’t have an Apple II mouse, just plug in a USB mouse, and it will work fine.

What monitor do I use with the Apple II Pi?

Here you have some options: the default would be to use the HDMI output of the Raspberry Pi to plug into a DVI or HDMI monitor/TV.  The composite port of the Raspberry Pi was compromised to allow clearance for the HDMI port.  With a hacked up video cable and a soldering iron, you can connect the composite video cable directly to the Raspberry Pi board and plug into a composite monitor.  In some cases, it can be useful to have a composite monitor plugged into the Apple II output for running the Apple II Pi configuration program or for developers who want to run code directly on the Apple II (and see it’s output).

Is the Apple II Pi interface adapter required to run the Apple II Pi software?

No, the Apple II Pi software uses the Super Serial Card’s 6551 chip in a special, high-speed mode.  The Apple II Pi adapter card simply has a Raspberry Pi header for connecting the Raspberry Pi to provide the serial port interface and power.  To the Apple II software, the Apple II Pi interface adapter looks like a firmware-less Super Serial Card.  An Apple IIc with a functional serial connection between itself and the Raspberry Pi will work with the Apple II Pi software just fine; some additional parameters may need to be set in the client and/or server software.

Is the Apple II Pi Open Source?

Yes, all the code is available here: http://github.com/dschmenk/apple2pi

Does the Apple II Pi just accelerate the Apple II?

Not in the way a traditional Apple II accelerator would.  Because the Raspberry Pi is always running Linux, some configuration has to be made to give the illusion of being an Apple II accelerator through the GSport emulator.  But its strength is in bringing modern CPU+GPU hardware and a modern 32 bit OS (Debian Linux) to the Apple II platform.

Does the Raspberry Pi provide any services to the Apple II?

Update: New functionality has been added to the software that give the Apple II additions ProDOS drives through the PiDrive interface to the Linux daemon.  Once a connection has been established between the Apple II and Linux, the Apple II client can exit back to ProDOS and still have the addition virtual PiDrives available for reading & writing. The virtual drive images can be changed from Linux.

No, the Apple II is slaved to the Raspberry Pi as a dedicated I/O processor.  The Raspberry Pi’s network connection, memory, storage, etc. are not made available to the physical Apple II.  However, the GSport emulator can make use of the Raspberry Pi’s memory and speed, as well as many peripherals attached to the physical Apple II.  Any USB devices won’t be seen by the physical Apple II, but can be used by the GSport emulator.

Does the Apple II provide any services to the Raspberry Pi?

Yes, the Apple II is slaved to the the Raspberry Pi as a dedicated I/O processor.  Besides the keyboard and mouse input, the Apple II Pi uses a custom protocol that allows Linux applications and drivers to access the Apple II memory and execute arbitrary code on the Apple II.  This flexible protocol is how the Linux joystick driver was written and how the FUSE (File system in User SpacE) driver provides ProDOS volumes as Linux directories and files.  Additionally, some of the provided tools that come along with Apple II Pi allow interacting with AppleSoft BASIC running on the physical Apple II and running arbitrary 6502 binaries on the Apple II.

Do I have to learn Linux to use the Apple II Pi?

Depending on how your Apple II Pi is configured and how you plan on using it: maybe.   Because the Apple II Pi is always running Linux, you will have to interact with it at some level.  If your setup is configured to automatically run GSport and then shutdown, there isn’t much you have to learn except logging in.  However, the strength of the Apple II Pi lies in the fact it is running Linux, an industrial strength, modern operating system.  To use the full capabilities of the Apple II Pi requires interacting with Linux and the X Window System.  There are a large number of quality and free applications available for productivity, entertainment, programming, and education.  All of them are directly available for download to your Apple II Pi (http://www.debian.org).  This spirit of openness is what Woz had in mind when he developed the Apple II in the first place.

How do I access my Apple II storage media (floppies, SCSI drive, CFFA, etc.)?

By leveraging the FUSE (File system in User SpacE) subsystem, all the ProDOS volumes can be mounted in your user directory.  The filenames are munged in a similar manner to the way CiderPress manipulates the names.  In addition, the raw devices are available for making full volume copies and usage with emulators.  Both floppy drives in slot 6 show up as raw devices regardless of the type of format so that emulators can access non-ProDOS formatted floppy disks.

What is the point of the Apple II Pi?

To be able to use Apple II hardware in a more modern environment.  Although it is possible to use the Apple II as a terminal to a Linux computer, it doesn’t provide much of a modern GUI environment or digital compatibility with flat panel monitor/TVs.  Just as GS/OS brought a functional 16-bit GUI to the Apple IIgs (with 8-bit compatibility for Apple II programs), Apple II Pi brings an up-to-date 32-bit GUI and OS to the Apple II (with 8-bit and 16-bit compatibility by way of the GSport emulator).

Additional information:  There are other projects that may also be of interest.  Ivan Drucker has bundled up David Schmidt’s ADTPro along with some other functionality in his A2CLOUD project:



Using your Apple II as a Linux terminal:


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