ACSI2STM: Atari ST ACSI hard drive emulator

This code provides a hard drive emulator for your Atari ST using an inexpensive STM32 microcontroller and a SD card.

The aim of this project is to be very easy to build, extremely cheap, reliable and safe for your precious vintage machine.

The module supports up to 5 SD card readers, showing them as 5 different ACSI devices plugged in.

It can work in 2 ways:

• Expose a raw SD card as a hard disk to the Atari.
• Expose a floppy or hard disk image file on a standard SD card to the Atari.

It also provides an UltraSatan compatible real-time clock if you add a simple 3V lithium battery.

WARNING, the pinout has changed for version 3.xx. If you built or bought a unit for older firmware, you need to make changes. See the last section of hardware.md for more information.

Documentation

The doc directory provides documentation for the end-user as well as hardware implementors or curious people.

This is what you can find:

• manual.md: A brief user manual for people owning a unit.
• a2setup.md: User manual for the ACSI2STM setup tool.
• pcb_manual.md: User manual for the official PCB.
• compiling.md: A step-by-step tutorial to compile and upload a new firmware. Also includes how to customize the firmware for non-developers by changing compile-time options.
• build_pcb.md: Instructions for building an unit using the official PCB.
• hardware.md: How to build an acsi2stm unit from scratch.
• debug_output.txt: A sample output of the logs you should get when booting a SD card.

To people buying/selling hardware

There are people building and selling products based on this code. This project is not directly related to any of these people, there is no official hardware supplier.

Building and selling units is encouraged, as long as the spirit of free software is preserved and the terms of the license are respected.

The code here is released under the GPLv3 license (see LICENSE file). This has some implications:

• If you bought a product that contains code based on this project (modified or not), you can request the source code to the firmware contained in your product. The seller/maker of the product is legally required to provide it.
• If you sell any product based on this code, you must provide a link to the source.
• If you sell any product based on a modified version of this code, or reusing parts of this code, you must provide a link to the whole source code of the modified version with the product, including any additional features/modules you may have added.
• If you redistribute binary versions (modified or not), you must provide a link to the source code matching exactly the binary you redistribute.
• Any modified version must retain the GPLv3 or a compatible license.
• The name ACSI2STM is not protected. You can reuse it as you wish. Making a clear distinction between this code and your product will be greatly appreciated (most sellers do).

Credits

I would like to thanks the people that put invaluable information online that made this project possible in a finite amount of time. Without them, this project would have not existed.

• The http://atari.8bitchip.info website and his author, who also contributes on various forums.
• The Hatari developpers. I used its source code as a reference for ACSI commands.
• The UltraSatan project for their documentation and their RTC clock tool.
• Uwe Seimet for his SCSI testing tool.
• Jean-Louis Guérin (DrCoolZic) for his excellent "Atari Hard Disk File Systems Reference Guide".
• Sr Antonio, Edu Arana, Frederick321, Ulises74, Maciej G., Olivier Gossuin, Marcel Prisi and Tomasz Orczyk for their very detailed feedback that helped me a lot for fine tuning the DRQ/ACK signals and other various aspects of the projects.
• All people contributing on GitHub, for their code, their ideas, the issues they submit, and their patience when things fail !