ACSI2STM: Atari ST hard drive emulator

This project is 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. A lot of effort has been put in the documentation, both for usage and technical aspects.

It can work in 3 ways:

• Mount standard SD/SDHC/SDXC cards on the Atari (FAT16/FAT32/ExFAT).
• Expose raw SD cards as ACSI hard disks connected to the Atari.
• Expose ACSI hard disk image files as hard disks connected to the Atari.

It also provides an UltraSatan compatible real-time clock if you add a simple 3V lithium battery such as a CR2032.

The hardware is a custom PCB that can be order preassembled directly from JLCPCB. See quick_start for more information. The PCB attaches directly on the DB19 port at the back of your ST. The PCB has 3 microSD card slots, and the code supports up to 5 SD card readers.

Due to many issues with counterfeit or defective Blue Pill boards online, building new designs/units based on Blue Pill boards is discouraged.

Legacy hardware based on Blue Pill designs are supported to various degrees. All units that were built for firmware version 3.00 and later can be upgraded to the latest version. Units built for firmware version 2.xx need the legacy variant. Units built for firmware 1.xx need hardware modifications.

It can also work on STs with broken DMA chips by using the PIO firmware.

See RELEASE NOTES for details about the current version.

Final version: Both software and hardware parts are considered finished, the project is now mature. Feedback is still welcome and occasional bug fixes may be released.

Documentation

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

This is what you can find:

• quick_start: A tutorial to order the hardware, flash the firmware, using the unit and upgrading the unit.
• tutorial: A tutorial about using hard drives on an Atari ST if you never used one before. It will help setting up various hardware combinations.
• standard_configurations: Instructions to setup ACSI2STM depending on your hardware and what you want to achieve.
• tools: Documentation for tools provided with ACSI2STM.
• compatibility: Information about hardware, firmware and software compatibility.
• troubleshooting: Having problems? Have a look here.
• gemdrive: Technical details about GemDrive. How to mix GemDrive with ACSI. How to install GemDrive for EmuTOS.
• jumpers: Documents the various jumpers available on the PCB
• firmware: Describes the many firmware variants pre-built in the release package. Also provides a step-by-step tutorial to compile and customize firmware yourself.
• hardware: How to design and build an acsi2stm unit from scratch (hand wired, or your own PCB design). Also documents jumper configuration.
• protocols: Technical details about the communication protocol between the ACSI2STM unit and the Atari ST.

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).
• The code is provided without warranty, so hardware troubleshooting is best effort. If you bought a unit and you have issues, you should contact the seller first. Anyway, constructive feedback (including bug reports) is always appreciated.
• If a seller refuses to provide the sources, please open a GitHub issue to let me know.

Note: the Mega STE PCB is copyrighted by Olivier Jan and is released under the MIT license so it does not have the same restrictions.

If you sell ACSI2STM units, please consider selling the new compact PCB design instead of custom designs. If the compact design isn't to your taste, please open a GitHub issue and talk about possible improvements.

Credits

I would like to thank 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. I would also like to thank people giving feedback, contributing to make the project better.

• Bill Greiman for the SdFat library. It's really fantastic.
• 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, as well as the excellent GEMDOS drive implementation.
• The people who made the FreeMiNT TOS documentation.
• The EmuTOS developers, again the source code is an excellent reference.
• 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".
• mamejay, Ben Leggett, S0urceror, 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 !
• Olivier Jan for the Mega STE PCB.
• Tomasz Orczyk for finding a way to have a much better version of GCC and a lot of feedback.
• Joe Ceklosky for his feedback and help on fixing RTC issues.
• François Planque for his extensive explanation about the Mega STE internal drive