How floppy change detection works with Gotek, GOEX, HxC ?

[ParanoidLittleMan]

One recent post here reminded me on floppy change detection - possible problem with HW floppy emulators, like Gotek, GOEX, HxC .

Description is here:  http://atari.8bitchip.info/flomodam.html

And I guess that these emulators are done as PC floppy compatible. And possible that it is matter of firmware that they act as Atari compatible floppy drive.

 

Why it is problematic, and how to detect is it work properly or not:  TOS keeps some floppy data in RAM (cache), to make work faster. Like directory sector(s), FAT sectors (which hold file allocation on disk), and both give info about free areas on disk. If you change floppy, and it is not detected then there is a trouble: write can go on very wrong place, corrupt existing data, structure.

How to detect: I guess this should work, and easy to see when it is bad:  prepare 2 ST image files, 360 KB format is enough.  1 empty, and one with some data on it - like only 1 file, and it can be even DESKTOP.INF renamed to SOMEFILE or whatever.   Then select empty one, open it in Desktop and click 'Save Desktop". Before confirmation replace image to not empty one, click and then should see both files on Desktop. If see only DESKTOP.INF it means that disk change detection works not, and that your SOMEFILE is destroyed, + disk structure is bad too.

[ParanoidLittleMan]

Little correction and more help about how to do floppy change detection test simply and properly:

Prepare 2 empty 360 KB ST floppy image files. Or use this: 360AGA.zip

To have 2 of them need to copy it with different name to same DIR, then copy them to your Gotek SD or what storage it uses.

Set first image and open it in Desktop, will no see files. Then Save Desktop . Rename DESKTOP.INF (or NEWDESK.INF in case of TOS 2.06) to SOMEFILE or whatever you like. Replace active image to other one (which is still empty). Press Escape to refresh. Should get A: without files.

Now replace image to first one. Save Desktop. If change detection is OK will see both files. If not will see only DESKTOP.INF.  Yes, other one is destroyed. 

And to be sure: 

With this image (360AGA.ST) empty one has 360448 free bytes.

With 1 short file: 359424 free bytes.

With 2 short files: 358400 free bytes.

With 1 short file and corruption: 358400 free bytes.

Yes, the last one is 100% when disk change is not detected, file disappeared from DIR, but still takes space on disk. In normal usage it will be much worse - files might be seemingly there, but corrupted, with  overwritten parts.

 

[ijor]

It is not fixed at the hardware. It all depends on the firmware and we have more than one, now. I don't remember the details in each version, and later versions are highly configurable, so they might even allow you to configure the exact behavior.