1.3 High Density Patch

[Crispy]

I recently had a need for an external drive for my A1000. I remembered that I had one in the back room, and that it didn't work the last time I tried using it. After digging it out, I ended up repairing it by replacing the drive mechanism with a Chinon FZ-357A high density drive that I had laying around. That was an adventure in itself; perhaps I should write a post about it.

So now that I had a high density drive attached to my A1000, I thought that it would be nice to be able to use high density disks. Unfortunately the 1.3 trackdisk.device only speaks double density. "No worries, there must be something on Aminet." A quick search revealed Hackdisk, which is a replacement for the trackdisk.device, and does have support for high density disks. I tried it, and it worked, to an extent, but there were some things that I didn't like about it. My main gripe is that if you reboot the machine without a disk in the drive, then it kills that drive until you reboot with a disk in the drive. There were also some minor incompatiblities, mostly with messydisk.device which is used for reading and writing MS-DOS formatted disks.

I knew that I would eventually tire of the quirks inherent to Hackdisk, so I decided to set about patching the 1.3 trackdisk.device so that it would speak both double density and high density. The result of this work is a tool that I call TrackdiskHD. This tool reads in the currently running Kickstart, patches the trackdisk.device, and then writes the patched Kickstart to disk. It can either save to a file, or create a Kickstart disk.

Now I can read and write Amiga formatted high density disks on my A1000.


And I can also read and write MS-DOS formatted high density disks.


I'm making this tool available here for anyone wants to give it a try. Hopefully some of you will find it useful.

TrackdiskHD.zip

(13.47 KiB)

[dalek]

Nice work! Good to see some 1.3 love

[fxgogo]

That is amazing. Well done. I don’t have an HD disk drive to test it on, unfortunately. So let me ask a possibly silly question. If swapped out my A500 drive for a standard PC floppy disk, would it be possible to tweak your device driver to work with it? Could this be a way to enable standard floppy drives in the Amiga?

[Crispy]

If swapped out my A500 drive for a standard PC floppy disk, would it be possible to tweak your device driver to work with it? Could this be a way to enable standard floppy drives in the Amiga?

Unfortunately no. The Amiga high density drives were specially made by Chinon for Commodore. When you insert a high density disk into one of these drives, it causes the motor to spin at half-speed (150 RPM). The Amiga is still transferring bits at the double density rate, but since the disk is spinning at half the speed the bits are packed onto the magnetic surface with high density bit spacing.

Standard PC drives always spin at 300 RPM, and for high density disks data is transferred between the drive and the computer at about 1 Mbit/sec. This is a data rate that the Amiga disk controller cannot achieve.

This does give me an idea for a hardware project though. I wonder if it would be possible to design a board that plugs in between a standard PC drive and an Amiga, buffers the data, and then transfers it at the correct bit rate to and from the drive. Hmm...

[Zippy Zapp]

This does give me an idea for a hardware project though. I wonder if it would be possible to design a board that plugs in between a standard PC drive and an Amiga, buffers the data, and then transfers it at the correct bit rate to and from the drive. Hmm...

That sounds interesting. I had thought this too as to why they had to go through the effort of changing the drive itself versus adding or changing hardware on the Amiga side to accommodate HD mechanisms. Apple was putting HD drives in Macs in 1988 and later.

[McTrinsic]

This is awesome. I plan on using a flash rom solution for my current Amiga hardware project.

Looking forward to use a custom 1.3 ROM with this included.

Thanks for sharing!!

[intric8]

This is WAY cool!

Hey - that mouse pointer! Hah! Love it

[jaudron2]

Do you find it risible... when I name my hard drive... Biggus Diskus?

[pgovotsos]

This does give me an idea for a hardware project though. I wonder if it would be possible to design a board that plugs in between a standard PC drive and an Amiga, buffers the data, and then transfers it at the correct bit rate to and from the drive. Hmm...

Somewhere I've seen that someone has already made a little board to do this. I don't have the link on hand but I will hunt it out and post it here.

I found this on Amiga News. In the article it mentioned some limitations of this.

"In order to add the new code into the Kickstart, the support of 5,25 inch drive was removed. Additionally, the trackdisk.device no longer warns if some of the required system ressources are not available for initializing it."

Is this still true? Can you expand on the "no longer warns" part? What specific conditions and why removed? Are there any other limitations compared to the standard trackdisk.device? I actually do use a 5.25 drive on my 1000 with Transformer.

Was the reason for removing things to make it fit in the Kickstart chip? I have accelerators that I can flash a Kickstart file to - even ones larger than the standard 1000 Kickstart ROM. Would it be possible to make a version that does not have these features removed?

Does this work with both internal and external drives?

[McTrinsic]

If you have to opportunity to Flash the ROM in your accelerator card then you can simply use Remus to exchange the old trackdisk.device from 1.3 with the one from 2.05.