I want to run Dangerous Dave on a physical IIe, and before I load it to a disk, I want to make sure the image I have is valid.
The image is from here: https://archive.org/download/a2_asimov_dangerous_dave and when I run it in the emulator, I get the screenshot https://archive.org/download/a2_asimov_dangerous_dave/a2_asimov_dangerous_dave.gif, which appears to be the monitor asterisk prompt
How can I get the game running? Is this some anti-copy protection measure?
Thank you!
I picked up dangerous_dave.dsk from that site, and it ran without complaint in AppleWin. What emulator are you using?
Thank you for trying it out! I am using http://www.virtualii.com It only runs on OS X, I believe.
I was suspicious that the Archive.org screenshot (I assume it is auto-generated) showed the same thing, but perhaps we are both using the same, broken emulator.
Did you use an Apple IIe emulator? Perhaps this is an issue with the configuration? Perhaps with/without language card? I will try other emulators.
I have tried one other emulator (http://openemulator.org/index.php/category/openemulator/, with download here: https://code.google.com/p/openemulator/downloads/detail?name=OpenEmulator-1.0.3.dmg&can=3&q=) with and without the language card. It's only an Apple ][+ emulator. Same screen!
https://www.dropbox.com/s/ptoememdmd557k8/Screenshot%202015-09-16%2017.46.40.png?dl=0
Try renaming dangerous_dave.dsk to dangerous_dave.po and see how that works in your emulators.
That did work in the emulator! Thank you.
I found [1] explaining what these file formats are. At first I thought they aren't just disk images like an .iso because the Apple II has low-level access to the floppy drives, and so there are different formats. But it seems like the story is different, is that right?
[1] http://apple2.org.za/gswv/a2zine/faqs/Csa2FLUTILS.html#006
Yes, it's little different. There are two different flavors a 140k disk image can come in, and it has to do with the sector interleave (usually called ordering in this context - "DOS order" or "ProDOS order"). The file suffix .po gives a hint that it's in ProDOS order, and .do gives a hint it's in DOS order. The more generic .dsk doesn't specify which it is. So most modern tools and emulators are capable of figuring that out for themselves; there are a few rules that make it pretty clear internally which is which, so it's surprising that Virtual II wasn't capable of making the correct choice.
Ah, I see. Thank you for that explanation!
If the emulator were faithfully emulating all the timings, including the timing of the floppy drive disk spin motor, then the emulator wouldn't need to know the interleave order, right?
That's true, but it's more complicated than that. The .dsk/.po/.do form of disk image only encapsulates the data that is within the data marks on the disk - and none of the meta-characteristics, address marks, and so on. So these pure data forms do in fact care about the order in which the bits were lifted off the disk, so as to correctly interpret them.
Another form of disk image we haven't addressed yet is the "nibble" (or .nib) form. It does take into account some of the timing characteristics, and address as well as data marks on the disk surface. As such - it does not have an "order," as the only order is the order in which the bits pass under the read head (which is not true of either .po or .do). The .nib is still not a perfect (or even great) encoding scheme; it is somewhat lossy, and there are still tons of characteristics of the Disk II that it cannot encapsulate.
One fundamental problem we have with the Disk II in general is that not everything that can be read (or at least sensed) by the Disk II controller is possible to be written by that same controller - even discounting physical harm such as pinholes.
Fascinating stuff! Thank you for the careful replies.
If there are any other documents about this, or perhaps how this might affect the emulation of software with clever anti-copy schemes, I'd be interested in reading them!
If you truly want to understand the wonder that is the Disk II controller... you need to read and understand chapter 9 of Jim Sather's "Understanding the Apple II" book:
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/Books/Jim%20Sather%20-%20Understanding%20the%20Apple%20II.pdf