REQUEST: Demos

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Par sdsnatcher73

Prophet (2353)

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09-09-2021, 21:38

About your loader, is that dependent on track 0? Or is it itself just a .COM file that is loaded once CP/M has booted?

Par sdsnatcher73

Prophet (2353)

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09-09-2021, 22:14

This is an interesting read. Basically the pre-sector data tells the size of the sector. Any MSX may be able to read 128bytes sectors I think (the BDOS might handle that). The BDOS is already quite clever, e.g. a turbo R is able to read a double sided, single density disk which has only 40 tracks. Then again because of MS involvement a 512bytes per sector may be hard coded in the BDOS.

Par NYYRIKKI

Enlighted (5889)

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10-09-2021, 03:35

MR.HAWARD2.0 wrote:

Yes, but if I get a Gotek drive connected to the SV328 I could (maybe?) do a full disk copy from one of the 5 1/4" drives (including the annoying track 0) to the Gotek. And if Gotek save the disk image as a readable file on the USB disk I'd get a full image (including track 0).

Yes, I think you are likely right... Is the disk image on the USB drive in a format you can insert in to any existing SVI emulator or so? That I'm not quite so sure, but I'm definitely willing to help.

I think the situation currently is pretty horrible... AFAIK BlueMSX supports only pure data dump and does not care of different data formats. The "DSK-image" is just dump of all data stored from all sectors starting from first to last sector and track... and yes, that can be a pretty noticeable problem... OpenMSX is a bit more accurate... it uses ".DMK"-files that really contain lots of more information of tracks and sectors, but unfortunately it is also completely ignores the sector FM/MFM encoding problem.

Quote:

Wait a minute. The SV738 uses the same FDC chip as SV328 right? So it should also be able to handle track 0 (128 bytes/sector)?

The byte count is not the problem. I'm not expert on these kind of details, but IIRC the FD1793 chip on SVI-738 would need separate clock source to read the FM-data... and that was the missing part.

Par NYYRIKKI

Enlighted (5889)

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10-09-2021, 04:22

sdsnatcher73 wrote:

This is an interesting read. Basically the pre-sector data tells the size of the sector. Any MSX may be able to read 128bytes sectors I think (the BDOS might handle that).

Yes, on normal tracks less common sector sizes might be possible... I remember trying another way around and SVI-328 SV-BASIC was perfectly capable to read PC/MSX formatted 512 byte sectors... Ok, ok... the extra 256 bytes trashed the system variables so that the computer crashed at first try, but after fiddling with MAXFILES-command, I managed to make it work ok. Too bad SVI-328 doesn't understand anything about FAT-filesystem.

Par NYYRIKKI

Enlighted (5889)

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10-09-2021, 05:11

sdsnatcher73 wrote:

how would you copy such a floppy to another one (using real hardware)? Would it be formatting a disk with that hardware and copying the files?

On SVI it is quite a bit harder than on MSX... First you had to format the disk physically... Originally this could be done only under CP/M, but later ML programs appeared to do it on BASIC... at least for common drives. After that you needed to format the disk logically... For this purpose a BASIC-program was delivered, but you needed to know that it is correct version. After that you needed to transfer correct version of Disk-BASIC it self from old disk to new disk (another BASIC-program was delivered for that)... After all this you could manually copy files one by one to new disk... Yes, it really does not sound like user friendly, but I think CP/M users were a bit more lucky.

On "normal" SVI-328 disk the Disk BASIC is the thing that stays on track 0... Ok, track 0 is not enough for it, so loading continues from, but if in you mind something like track 0, sector 0 could tell you something about the hardware, how many reading heads you need, what physical track limitations you have, or something like that then... No... No, no, nothing no, there is just some code that is executed..

Par sdsnatcher73

Prophet (2353)

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10-09-2021, 09:11

Interesting stuff indeed and imho worth to contact the FlashFloppy developer to add support (he has added support for many odd formats used on Synthesizers and odd old computers Wink this may even be relatively easy. Still as a first step (and easier to achieve) I would still copy just the executable COM files so at least those are preserved. We can then try running them in either MSX-DOS or CP/M 3.0 on other MSX hardware…

Par wouter_

Champion (469)

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10-09-2021, 09:58

NYYRIKKI wrote:

... OpenMSX is a bit more accurate... it uses ".DMK"-files that really contain lots of more information of tracks and sectors, but unfortunately it is also completely ignores the sector FM/MFM encoding problem.

That's right. In principle the .DMK file format supports both FM (single density) and MFM (double density) sectors (even mixed within the same track), but openMSX currently only implements the MFM part.

NYYRIKKI wrote:

The byte count is not the problem. I'm not expert on these kind of details, but IIRC the FD1793 chip on SVI-738 would need separate clock source to read the FM-data... and that was the missing part.

The WD179x/WD279x family of disk controllers have an input pin called DDEN# (e.g. pin 37 on WD2793) that selects between FM (single density) and MFM (double density) mode. If I remember correctly both use the same clock of 1MHz. But there are other disk formats (e.g. high-density) that do require a 2MHz clock.

On most MSX machines this pin is hardwired to GND, meaning only MFM (double density) mode is possible.

On the other hand the TC8566AF disk controller (e.g. used in turboR machines) allows to select between FM and MFM mode in software (it's a parameter in e.g. the read-sector command). I don't believe the turboR disk ROM implements support for FM sectors, but I could be wrong. I tested by creating a DMK image with all unformatted tracks, and then try to read from this disk. This fails of course. But during the attempt the turboR software only issued MFM read-sector commands.

Because FM sectors are rarely used on MSX, it's not a high priority to add support for this in openMSX.

Par sdsnatcher73

Prophet (2353)

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10-09-2021, 10:32

If I understand it correctly FM vs MFM has nothing to do with single or double density formats, but terminology is sometimes used loosely. Single density (as I understand it) refers to 40 tracks formatting as opposed to double density being 80 tracks. The National FS-4600F, FS-4700F, FS-5000F2, FS-5500F1 and FS-5500F2 machines have support for formatting single density disks. An FS-A1ST (and probably other machines but I have not tested) was able to boot MSX-DOS from a disk formatted as double sided/single density (360kB) in my FS-5000F2.

FM and MFM are modulation techniques. It may be and probably is true that single density disks use FM modulon and double density disks use MFM but the difference in density is not achieved by the difference in modulation as the bit clock for both modulations is identical.

Par wouter_

Champion (469)

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10-09-2021, 12:34

sdsnatcher73 wrote:

If I understand it correctly FM vs MFM has nothing to do with single or double density formats, but terminology is sometimes used loosely.

It seems we're both right:

I based myself on the WD2793 datasheet, and it associates 'single density' with FM and 'double density' with MFM. But according to this wikipedia article the term "density" was originally used for FM/MFM encoding and later for "other" physical characteristics (e.g. like track-density).

It's true that (in this context) the output bitrate for FM and MFM is the same. But MFM is a more efficient encoding: it can store twice as many logical bits than FM encoding (at the same output rate). That is: when using material with the same magnetic coercivity (roughly speaking: the same minimum distance between two magnetic flux reversals) you can store twice as much information when using MFM encoding compared to FM encoding. In that sense 'double density' seems an appropriate term.

Par sdsnatcher73

Prophet (2353)

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10-09-2021, 14:55

So now I wonder what single density on the National machines is. in theory it could mean 40 tracks with MFM encoding but also FM encoding on 80 tracks… how could we find out? Are there tools for MSX or PC that can reveal information about the physical formatting of a disk?

Okay just formatted 2 disks, 1 single sided/single density and 1 double sided/single density. In both cases the drive steps 40 times instead of the usual 80 times. So definitely it is 40 tracks. I am installing a linux VM to see if getfdprm from fdutils can give some more details.

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