Back to the Future MSX2 and emulators

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Door SLotman

Paragon (1238)

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04-05-2021, 11:07

If you try to run the "Back to the Future" MSX2 game (from my site) on both BlueMSX and OpenMSX... it won't work. The game falls into BASIC and that's it.

The same DSK does work on RuMSX - and I just tested... on WebMSX as well!

The weirdest part? The game seems to be made in BASIC. AUTOEXEC.BAS loads *nothing* on BlueMSX and OpenMSX - but on RuMSX and WebMSX I can see the source. It's not some 'code' hidden in the boot sector running before going into MSX BASIC either - I booted with other disk, then replaced it with BTTF and I still couldn't read AUTOEXEC.BAS, or any other file in BASIC on the disk.

What is going on here?!

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Van SLotman

Paragon (1238)

afbeelding van SLotman

04-05-2021, 13:19

Hmmm. If I extract the DSK contents into a folder, I can read the BASIC files. But the game doesn't start, it locks on a black screen.

Ok... black screen is due to copy protection. And it seems the code to load images from disk are in the same binary as the protection - the game seems to read the images directly from specified sectors, that's why extracting them to a folder won't work.

Doesn't explain why the BASIC files won't load, though.

Van SLotman

Paragon (1238)

afbeelding van SLotman

05-05-2021, 19:59

Nobody cares about this game that runs on real hardware, on RuMSX, WebMSX but not on BlueMSX or OpenMSX? oO

Van Grauw

Ascended (10056)

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05-05-2021, 20:14

Have you tried emulating different machines?

Van tfh

Prophet (2971)

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05-05-2021, 20:26

LOL... Quite strange indeed.
The .ROM image of the game (a ROM2DSK conversion) runs fine on OpenMSX.

Van turbor

Champion (485)

afbeelding van turbor

05-05-2021, 21:37

Is it a single sided disk but the file is 720KB?
I had some other dsk files that were created by a disktool that didn't correctly handle 360Kb disks. but the first track (first 9 sectors) containg the FAT and directory will be correct, so you can see the data but actually loading will fail in an emulator due to the way it calculates offsets in the dsk file. If you rewrite such an incorrect 360KB disk back to a real floppy with such a faulty tool it will work on a real MSX again...

Van gdx

Enlighted (4693)

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06-05-2021, 02:07

The archive found on MSX2.ORG is broken.

Van Jipe

Paragon (1502)

afbeelding van Jipe

06-05-2021, 10:41

if you split the dsk in two part you have the original 360k files and it work on BlueMSX
in CPU.OBJ you can see the program use call F37D to read sectors
0e1a ld c,1ah set dma
1100d9 ld de,0d900h
cd7df3 call 0f37dh
ed5b00dc ld de,(0dc00h)
13 inc de
ed5300dc ld (0dc00h),de
1b dec de
0e2f ld c,2fh absolute disk read
210001 ld hl,0100h
cd7df3 call 0f37dh

Van gdx

Enlighted (4693)

afbeelding van gdx

06-05-2021, 11:20

turbor wrote:

Is it a single sided disk but the file is 720KB?

You are right. The file must be trimmed to half the size and two byte D0 02 at 00013h replaced by 68 01 to work and get a correct image.
Someone must have modified this game without checking. It's amazing that the most sites uploads this bad version.

Van tfh

Prophet (2971)

afbeelding van tfh

06-05-2021, 14:16

Thanks GDX for solving this. I've placed a fixed version on my download archive.

Van Jipe

Paragon (1502)

afbeelding van Jipe

06-05-2021, 15:49

why change D0 02 at 00013h and replace by 68 01 ?
a disk 360k have 720 sectors (2D0h) 0 to 719
a disk 720k have 1440 sectors (5A0h) 0 to 1439

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