Steven Seagal's Atari ST Web Site


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"Hard To Spin"

  Development screen of Steem SSE 3.8.0  

Support for ACSI hard disk images




Much like ST files for floppies, some img files contain all sectors of an
Atari hard disk (data only).
Using those files allows lower-level emulation of hard disks in Steem.
The feature was already available with Pasti, but with some limitations.
ACSI (Atari Computer Systems Interface) was the SCSI-like interface between
the ST and a hard disk or a laser printer (not emulated).

  There are now 2 icons for hard drives: one for ACSI drives, one for GEMDOS drives, replacing the unique "Hard Drives" icon that was used for GEMDOS drives before v3.8.  

  Looks cool. Also, when you right click on those icons to toggle emulation on/off, they will remain in a selected state so that you see at once what's going on. 'HD' is still indicated in the status bar when one or more hard drives are active.  

  Like for GEMDOS drives, you left click to open the manager.

This is the part that demanded some C++ programming, deriving a class from the one doing the GEMDOS hard disks, and adding some fake RTTI to spare code footprint. Technical details but those are my brag webpages.


  Up to 4 virtual ACSI hard drives may be added. It could be 8, but unless there's a clamour for it, I'll keep it at 4. In the Atari doc, that's the maximum recommended.

ACSI devices are numbered from 0 to 3.

The size limit is 1GB. It ought to be enough for anybody.

It is also possible to enable GEMDOS virtual hard disks at the same
time as ACSI virtual hard disks, you need to adapt letters of course.
ACSI drives will take the first letters.
It's handy to copy files.
Transfer speed depends on Disk manager 'Accurate Disk Access Times' option,
but even when it's not checked, the ST operates slowly compared with a PC.

Note that unlike GEMDOS hard drives, each ACSI device may be split into several partitions (C:, D:...).




The legendary SH204 shoebox. You've got one too now, kid! (A SH204.img file is included in the download archive)


  20 MB! Yeah man! And all in one partition (this wasn't the default...)  

  Or maybe you prefer a Megafile 60?  

  You got it. One logical drive only on the supplied image (on the website).  

  This is the AHDI driver by Atari, but it also works with other drivers (not all drivers will handle multiple devices).
This is "ACSI" only, so no SCSI, no IDE, no "ICD" emulation, not sure those are necessary.

  It is even possible to format those disk images inside Steem (for advanced users).

A floppy disk image with necessary utilities is available here, so you can
see what I actually pass time with.



  - R/W are done in real time and byte per byte, so if you screw up there are chances the file will be saved as is (your risk). On the positive side, img files are easy to backup, and they compress very well.  
  - We use the already existing DMA object to take care of transfers. That is, we use a 'DRQ' (data request) function for every byte, this to simplify code, but it makes your computer work out.  
  - Emulation is straightforward: just fetch sector #n in a file. After all, the ST didn't need to know anything either about the physical drive. Even the Format command was totally managed by the controller. We emulate at interface level, not drive level.

When I see the simplicity of ACSI emulation compared with the GEMDOS way, I wonder if we, collectively, shouldn't have gone another way. Of course, it is very convenient as it is, but the ideal way would maybe have been to use a 3rd party file manager to edit ST hard disk images, and emulators would only handle simple image files.

  This 3rd party manager fortunately already exists, it is 'Drive image' by Petari.


  It does everything that is needed in our case (follow red arrows), and more if you will (USB keys).

GEMDOS hard disk emulation still works. At some point, I was willing to nuke it in Steem SSE!

If you use any TOS other than v1.04, 1.62 or EmuTOS, you will be warned, because Steem hacks work better with those versions.

Note that failure of those hacks to work with other TOS can't be considered a bug.



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