ACSI2STM   Quick-Start-Guide

​ACSI2STM Hard Disk for Atari ST

A modern hard disk solution for Atari ST/MegaST/STE/MegaSTE
The ACSI2STM is an open-source hard drive emulator designed for Atari ST computers, enabling the use of SD cards as storage devices. Powered by an STM32 microcontroller, it bridges the Atari’s ACSI port with modern SD cards, providing a cost-effective, reliable, and versatile solution for expanding storage on vintage Atari systems.​

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1 - Backup battery

 

Before installing, insert a CR2032 battery in the socket. The battery is only needed for keeping the clock running when the ST is off. See this video on how to insert the battery: https://youtu.be/rgAsQ0IYjlg

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Download CONTROL.ACC to set the time HERE.

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2 - Installing on the DB19 port

 

• Plug the unit on the back of the ST, components toward the keyboard. The mounting holes of the Hard Disk socket should be aligned.

• Put some screws to hold the unit in place (optional). If you need screws, you can unscrew the hex screws of the Modem or Printer socket.

• Power the unit via the USB-C port.

• Optionally, you can plug other devices such as an UltraSatan on the IDC20 socket.

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3A GemDrive mode - Using microSD card formatted in FAT32 

 

3A.1 - FAT32 microSD card

Using Fat and Fat32 microSD cards without any other action is known as “GemDrive” mode. This is the easiest way to use the card. It does not require any driver. The microSD card will be usable on a Windows PC (to transfer files to your Atari for example).

 

This mode has been tested and known to be working well on Atari ST, STE, Mega ST and Mega STE with TOS equal or above 1.04

 

That mode is not available on Atari TT030 and Falcon030 or ST with TOS 1.00/1.02
The TOS on these machines may not work in GemDrive mode.

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Just insert a FAT32 formatted microSD card on slot 0 and boot. You will get one drive with with one partition for each microSD card you insert. The size of the partition will be the size of the microSD card.

This mode is easy to setup and will work for most applications. If you are planning to use your hard drive for sampling/streaming, you may get better result and speed with the ACSI mode explained in sections 3B. 

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Here a short video showing how to use the card in GemDrive mode: https://youtu.be/_jP6d4z2Qq4

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Limitations
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* Truncates long file names, as TOS doesn't support them.
* Only one partition per SD card.
* Works around some TOS limitations by using (relatively safe) heuristics,
  but there may be issues in some very extreme corner cases.
* Hooks the whole system unconditionally: may decrease performance in some
  extreme cases. Also, the STM32 can stall the whole TOS in case of error.
* TOS versions below 1.04 (Rainbow TOS) lack necessary APIs to implement Pexec
  properly, meaning that running a program will leak a small amount of RAM.
  This is also the case in Hatari.
* File descriptors are leaked when terminating a process with Ctrl-C. There is
  no system call to catch this event.
* Not compatible with MiNT or any other TOS replacement.
* Not compatible with OS-level multitasking (MultiTOS, ...).
* Mimics TOS 1.04, TOS 1.62 and TOS 2.06 behavior (and some of its bugs), so
  software relying on other TOS versions can have issues.

 

3A.2 - Setting date and time

 

In GemDrive mode, you can use any tool to set the date, such as CONTROL.ACC or XCONTROL.ACC. GemDrive redirects all system calls to the STM32 so the internal clock isn't used anymore.

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3B ACSI mode - Using microSD card ACSI mode

 

Use a ready-made ACSI disk image.
If you have a bootable hard disk image, the following sections will describe how to use it.
These hard disk images are the same using by the HATARI emulator on PC and similar to the one used by UltraSatan.
They are also hard disk images preloaded with games and application available on the internet you can use the same way.
For copyright reasons, I only supply empty, ready to use images on this page.

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3B.1 - Transferring a disk image to a raw SD card

 

Using a raw SD card is a bit faster than copying the image file.

To transfer images to the disk, you can use Raspberry Pi Imager:

• Open Raspberry Pi Imager.

• Click Choose OS under Operating System.

• Select Use custom in the list.

• Select the image file you wish to transfer.

• Under Storage, click Choose storage.

• Select the SD card you want to write to.

• Click Write to start writing. Existing data on the SD card will be erased. Click Yes to confirm.

• The SD card can now be used on the ST.

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Here a short video showing how to setup an image with ICD Driver: https://youtu.be/kdNR6F6j5io

Here a short video showing how to setup an image with PP HDDriver: https://youtu.be/3sT4ueO1-7E

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Here is the ICD655 Driver

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3B.2 ACSI Images files:

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• Image ICD Demo 14Mb

• Image ICD 16Mb + 4x256Mb Compatible with TOS 1.02

• Image ICD 32Mb + 2x512Mb for TOS > 1.02

• Image HDDriver Demo 640Mb

• Image AHDI_BOOTABLE_16Mb_1x256Mb  (AHDI Driver used)

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3B.3 - Setting date and time

 

In ACSI mode, ACSI2STM emulates an UltraSatan clock, so you can use UltraSatan tools such as SD_GETCL.PRG and SD_SETCL.PRG (or US_SETCL.PRG and US_GETCL.PRG). GemDrive mode also responds to UltraSatan clock queries as a convenience. When the system is switched off, the STM32 clock is powered by the onboard CR2032 battery so it will keep time even when powered off.

Once your clock is setup, just copy SD_GETCL.PRG (or US_GETCL.PRG) into your AUTO folder.
You can get these programs from my UTILITY pack under the SD4ST folder. Download is here: UTILITY

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4 - Mixing GemDrive and ACSI mode

Yes, it is possible to mix both modes at the same time. This will allow you to copy files into a FAT32 microSD card from your PC, then mount it on your Atari along with a microSD card containing an ACSI image with your ACSI driver such as ICD. You will then be able to copy files between GemDrive and ACSI.
 

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Here an example using ICD driver (one of my ICD disk image)

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- On PC, download all the files you want and place them on a microSD card your formatted in FAT32.
The files and folders names cannot be longer than 8 characters.
Referrer to [3A.1 - FAT32 microSD card] section on how to use the GemDrive mode.
Insert that microSD card in the first slot of the ACSI2STM

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- Follow section [3B] to create a microSD card with an ACSI. You can download one of my ICD image, change the partition settings if you want. This second microSD is your ACSI drive.
Insert this second microSD card in to the second slot of the ACSI2STM

 

 -Power the ACSI2STM and start your Atari.

The display at boot time will be a bit different. A message about the your GemDrive being allocated to letter L is displayed

 

 

 

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This will allow any ACSI partitions to use letter C to K

Then your HD driver will be displayed and boot the ACSI part.

Now, on the desktop, select any drive and go to Options>>Install a disk unit. Type L as Identification. Then Install.

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A new disk icon shows up. It is your GemDrive with all the files you put on it. you can now copy files across all drives.

 
 

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Hardware compatibility

ACSI2STM was successfully tested on the following configurations:

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• Atari 520 STF, TOS 1.04, GemDrive + ICD driver

• Atari 1040 STE, TOS 1.62, GemDrive + ICD driver

• Atari 1040 STE, TOS 1.62, GemDrive + PP driver

• Atari 1040 STE, TOS 2.06, GemDrive + ICD driver

• Atari 1040 STE, EmuTOS, integrated ACSI driver + GemDrive

• Atari TT030, ACSI mode (driver not specified)

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GemDrive mode is currently tested on Atari ST and STE (no TT or Falcon). It might work on the TT or the Falcon. If anybody owns this hardware and is interested, please open a GitHub issue. Testing is safe for the hardware, not for data.

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TOS 1.02 is working with the ACSI2STM card only in ACSI Mode.

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TOS >= 1.04 ("rainbow TOS") is strongly recommended because older TOS will leak a small amount of memory when a program stops. It may or may not have an impact depending on how you use the machine.

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TOS replacements such as MultiTOS, MiNT or others are incompatible with GemDrive mode. Implementing multitasking in GemDrive is nearly impossible on such a small microcontroller.

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ACSI2STM was successfully tested on the following configurations:

• Atari 520 STF, TOS 1.04, GemDrive + ICD driver

• Atari 1040 STE, TOS 1.62, GemDrive + ICD driver

• Atari 1040 STE, TOS 1.62, GemDrive + PP driver

• Atari 1040 STE, TOS 2.06, GemDrive + ICD driver

• Atari 1040 STE, EmuTOS, integrated ACSI driver + GemDrive

• Atari TT030, ACSI mode (driver not specified)

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