A314

What is it?

A314 is a family of expansions for Amiga computers that lets a Raspberry Pi (RPi) be used as a co-processor to the Amiga.

The Amiga and the RPi communicate through a shared memory that resides on the A314 board. A communication protocol is implemented on top of the shared memory, that allows programs on the Amiga to establish logical communication channels to services running on the RPi. The protocol is handled by drivers on each side, a314.device on the Amiga and a314d on the RPi. The drivers are responsible for multiplexing packets from the logical channels and notifying the receiving side when a packet is available, using interrupts.

Hardware variants

Initially there was a single variant of A314 that connected to the trapdoor on an Amiga 500. Since then several more variants have been developed for different Amiga models. The same software run on the different hardware variants.

The design files for the different hardware variants are available in separate repositories. The currently available variants are:

Variant	Amiga model	Connector	GitHub repository
A314-500	Amiga 500	Trapdoor	https://github.com/Eriond/A314-500-PCB
A314-600	Amiga 600	Trapdoor	https://github.com/Eriond/A314-600-PCB
A314-1000	Amiga 1000	Front expansion	https://github.com/Eriond/A314-1000-PCB
A314-cp	Any Amiga with clockport	Clockport	https://github.com/niklasekstrom/clockport_pi_interface https://github.com/Eriond/clockport_pi_interface (alternative PCB layout)

The A314 software has also been adapted to run on the Musashi version of PiStorm.

What can you do with it today?

We have implemented a few services that run on the RPi and on the Amiga:

• a314fs is a file system that is mounted in AmigaDOS as the PI0: device. The volume in PI0: is called PiDisk:, and is mapped to a directory in the RPi.

• pi is a command that lets you invoke executables on the RPi from the AmigaDOS CLI. For example, if your current working directory is on PiDisk: and you run pi vc hello.c -o hello, then the vc program (the VBCC cross-compiler) is executed on the RPi with the given arguments. It will cross-compile hello.c into the Amiga executable file hello. The resulting binary is immediately accessible through the a314fs.
  You may also launch Interactive applications using the pi command, such as pi mc -a which will run Midnight Commander. Running pi without any arguments is equivalent to pi bash and will present you with a bash prompt from the RPi.

• PiAudio lets the RPi stream audio samples directly to the shared chip memory, from where Paula plays those samples. PiAudio is integrated with ALSA on the RPi so that any program that plays audio through ALSA can be used, i.e. "pi mpg123 -a amiga song.mp3" plays song.mp3 using the program mpg123 to the Amiga.

• RemoteWB works by moving the Workbench bitplanes over to the chip memory on the A314. This requires that the A500 has at least a 8372 Agnus. During drawing of each frame on the Amiga, the RPi reads those bitplanes, encodes them into a GIF image, and transmits that image to a web browser through a web socket. The web browser in turn, returns key presses and mouse movements back to the Amiga through the same web socket. In effect, this becomes a web browser based remote control application, comparable to VNC but with near zero performance impact on the Amiga CPU!

• VideoPlayer is a simple program that displays a sequence of images on the A500 by letting the RPi write bitplanes directly to the shared memory (this again requires that the A314 memory is chip memory, and not "ranger" memory).

• a314eth.device is a SANA-II driver that forwards Ethernet packets to the network interface of the RPi. Together with an Amiga TCP/IP stack this provides network access to the Amiga.

• a314disk.device mounts an ADF or HDF file on the RPi as a disk drive on the Amiga.

• PiHid takes input events from mouse and keyboard that are connected to the RPI with USB, and forwards those input events to input.device in the Amiga.

What could it potentially be used for in the future?

Here are some services that we have considered but not gotten around to implement:

• Networking through a bsdsocket.library implementation that forwards socket operations to the RPi and executes those operations there. This would give a higher degree of offloading than using the SANA-II driver with a TCP/IP stack running on the Amiga. The start of such a service is available in the libremote branch.

• Your ideas?

Do you want to get involved?

If this sounds interesting, you'll probably want an A314 of your own to play with. All the information needed to build boards is freely available in the hardware GitHub repositories linked to above.

The source code for the A314 software that runs on the Amiga and on the RPi is available in the Software directory.

There is a Discord server for discussing A314. Here's the invite link.