Writing original version of SD Snatcher to disk

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Por rderooy

Paladin (686)

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27-11-2018, 08:57

I recall that the original Dynamic Publisher also had some kind of copy protection where after I did the copy, I had to open some kind of disk sector editor (no idea anymore what the name of the utility was) to change some values.

Por Wild_Penguin

Hero (642)

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27-11-2018, 09:05

Uberjack: since your original disks are botched, why not use a crack and be done with it?

To write a working copy, you are going to need a working copy - so, it is a chicken-or-the-egg problem (and I've not seen a copy made with dsk-pro floating anywhere). To me it seems kind of pointless to write a fake copy protected disk; but, YMMV Smile

Por uberjack

Champion (312)

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27-11-2018, 09:05

NYYRIKKI wrote:

uberjack: There is no such thing as 100% copy... just like there is no two different coins that are identical. When you look close enough, you will always see a difference. The best copy that you can get is by using special hardware such as SuperCardPro or KryoFlux just like Louthrax suggested.

The original disks are damaged beyond any use (the media is actually so badly worn, you can see through it in places), so I can't copy them. About all I can do right now is assume that the DSK file I found earlier is the actual original file, and attempt to write it to floppy using "dd". Pardon my ignorance, but I was under the impression that DSK would be an accurate representation of the original medium (based on the fact that you can just "dd" the file to floppy).

Por uberjack

Champion (312)

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27-11-2018, 09:06

Wild_Penguin wrote:

Uberjack: since your original disks are botched, why not use a crack and be done with it?

To write a working copy, you are going to need a working copy - so, it is a chicken-or-the-egg problem (and I've not seen a copy made with dsk-pro floating anywhere). To me it seems kind of pointless to write a fake copy protected disk; but, YMMV Smile

Hehe, good point, and at the moment, that's what I'm doing. It's a silly distinction, but it just bothers me for some reason Smile

Por uberjack

Champion (312)

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27-11-2018, 09:09

Louthrax wrote:

Uberjack, that can be done, but you'll need special hardware for that (like a SuperCardPro or KryoFlux device).

Thanks, I suspected it might necessitate special hardware.

Por Wild_Penguin

Hero (642)

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27-11-2018, 09:45

A .dsk file is the actual representation of a standard formatted disk - without any error correction etc., as this data is reduntant in a disk image since the image is already on top of another layer. There is data on a disk besides the standard; and for all sane use (I don't consider copy protection as sane usage Tongue ) that data is not needed and is discarded from disk images. EDIT: this is a simplification in layman terms by another layman; someone might want to elaborate what it is that is (not) stored in a .dsk file, vs an actual floppy

But, I think you do not actually need special hardware, if you have an MSX with a floppy drive, the original (working) disk(s) and some mass media to write the image file with dsk-pro?

Por NYYRIKKI

Enlighted (5900)

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27-11-2018, 16:23

uberjack wrote:

Pardon my ignorance, but I was under the impression that DSK would be an accurate representation of the original medium (based on the fact that you can just "dd" the file to floppy).

No, not really... The DSK is just dump of all the disk's stored data, so usually 2 sides * 80 tracks * 9 sectors * 512 bytes = 737280 bytes. If we think of a single track the amount of stored data is therefore 9*512 = 4608 bytes. How ever the real amount of RAW data that can be stored on the track surface is about 6240 bytes +- few depending of situation.

If you think of a concept of "bad sector" you soon realize that computers don't know at all if some data is "good" or "bad" in nature... For computers data is just data and it does not really care that much if you give it a good working disk or a cream cracker. The way to rate if the data on disk is "good" or "bad" is to use CRC checksums that are stored after the "real" data. There is also other things such as headers, footers, sector numbers and gaps stored also there in order to make the computer to find the correct place and allow it to write data without destroying the whole track. This is the data that is written there when you "format" a disk. Usually this meta data is pretty much irrelevant to store since it is usually same on all disks, but the copy protections many times use "weird" meta data to make the disk operations to fail in certain way in certain situations.

rderooy wrote:

I recall that the original Dynamic Publisher also had some kind of copy protection where after I did the copy, I had to open some kind of disk sector editor (no idea anymore what the name of the utility was) to change some values.

This is kind of a very typical copy protection... It just checks if reading certain sector gives read error (=CRC check fail)... It was just implemented in quite a stupid way... You didn't actually even need to change anything... It was enough if you just ejected the disk from drive while DP was decompressing fonts. -> Causes read error -> Copy protection avoided! Big smile

Por TomH

Champion (327)

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27-11-2018, 22:14

I might be massively off-base with this, but if the only problem is just ensuring that a sector is bad, that's actually really easy to achieve regardless of your FDC type.

On a WD1793-type controller, you can use format track and just not issue the FF byte necessary to write a CRC for that sector. Assuming you don't need any of the other special-case values, you can also populate the sector with appropriate values. Also you can get the CRC wrong on either the ID or the data sections, at your discretion.

On either a WD or an 8272-derived controller, you can give a sector a bad data CRC as long as you don't mind its data content becoming undefined: issue a write sector command, supply at least one byte that differs from whatever is already on disk and then just stop supplying bytes. The write command will error out after having written the byte you supplied, and long before it would have updated the CRC. Though all bytes in the sector beyond the one or more that you supplied will now be undefined.

Actually, thinking about it, the WD relies on external circuity for drive selection so you can actually write arbitrary sector contents and end with a bad CRC: issue a normal write, provide the correct number of bytes to fill the sector, wait at least enough time for the final byte to be written, then change the active drive. As long as you divert at least part of the CRC you should be fine.

Por wernerkai

Champion (357)

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28-11-2018, 03:48

Hi folks,
I bought Snatcher boxed from Japan some years ago. When the box arrived I just gave it a try, because I can't read Japanese.
Tonight I made a dump of 3 disks with SuperCard Pro. With HxC Floppy Emulator Software I exported disk 1 as DMK file, then tried it in OpenMSX 0.14.0 with Sony HB-F1XD and Snatcher Sound Cartridge. It didn't work (!).

After that, I exported the same file as IMG, renamed to DSK and tried again in OpenMSX. This time the game booted OK.

The files are zipped in SNETCHAR.ZIP at my downloads page.

I can try to extract with READ-DMK or DSKPRO or DMK-CREATOR, if requested.

Regards,

Por uberjack

Champion (312)

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30-11-2018, 05:59

@wernerkai Thanks. I imaged SnatcherD1_scp.dsk to floppy and tried loading it in an A1WX. I got a series of alternating floppy reads, but nothing ever happened - the program just sat at the MSX BASIC boot screen. Same thing happens with and without the SD Snatcher cartridge.

I tried loading it in CocoaMSX, but the result was the same.

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