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View Full Version : Amstrad PCW8512 and gotek floppy emulators - is it possible ?



Sandisk78
June 22nd, 2017, 08:25 AM
Hi, all ! Going to buy an Amstrad PCW 8512. Onced my family owned one - it was my first computer from 1988 to 1994, when we bought a pentium-1 (a Digtital Starion300i, which now is part of my classic pc collection and is still in working cond.) But I never liked floppies and now, I consider that Shnider disks for PCW are hard to find and they must be in poor condition - so I wonder is there a solution for it, like a gotek floppy emulator ?

JonB
June 22nd, 2017, 08:52 AM
Yes, you can run emulators, but you need an adapter.

Also, there's this IDE interface which I designed, which makes the floppy question a bit moot
http://www.cpcwiki.eu/index.php/UIDE_Universal_IDE_adapter_cards_for_Z-80_computers

Although you still need the floppy to boot.

Sandisk78
June 22nd, 2017, 09:02 AM
Cool ! thanks for the answer !

Chuck(G)
June 22nd, 2017, 09:25 AM
You can also adapt a 3.5" 720K drive for use on this machines.

JonB
June 22nd, 2017, 11:07 PM
One more piece of advice: If you connect a drive to the PCW and you are using its power supply connector, beware. Amstrad have the +5v and +12v power lines swapped on their connector, so the machine will put 12v onto the drive's 5v line with predictable results.

Chuck(G)
June 22nd, 2017, 11:18 PM
Yup--I think I mentioned that a couple of years ago after a smoked Teac FD235F. :) Also, simply by changing a single byte in the boot sector of the CP/M system disk you can go from a 360K disk capacity to a full 720K.

Anyone interested in one of these beasts stateside? I've got one that's been sitting in a corner of my shop for years collecting dust. No printer, but this is a 120V unit--has the full 512K in it.

JonB
June 23rd, 2017, 12:57 AM
..simply by changing a single byte in the boot sector of the CP/M system disk you can go from a 360K disk capacity to a full 720K.

Which byte, what value?

Sounds like a useful hack to me, Chuck

:)

Chuck(G)
June 23rd, 2017, 09:07 AM
I'll drag out the floppies and do a comparison--alternatively, I can simply post the boot sector. Your choice.

GeoffB17
July 8th, 2017, 07:55 AM
Hm, I'm not sure that the 'patch' thing is quite true.

The Amstrad system expects a SSSD disk for A:, else it will not work. This is built into CP/M. CAN be more flexible with drive B: mind you. I had a 360k 5.25 drive as B: for a lot of years (still do, actually), and when my 3" A: drive failed I managed to get that drive working as A: (with a lot of help from John Elliott), but it HAD to be a SSSD format to work. Once the machine was booted, I was able to patch version 1.1 of the CP/M system (again, thanks John Elliott) so that the A: drive would accept the 360k format as well, but never able to get any other version of CP/M to do that.

Tweaking the XDPM data on the floppy will work within certain parameters, but not to conflict with things built into the .EMS system file.

Unless you're referring to some other byte in the boot sector? I'd be interested to know about that.

Oh, I'm VERY happily using JonB's uIDE adaptor, so my PCW is blessed with 13 @ 8Mb HDs! BUT, yes, still need the floppy to boot, but my 3" drive has been repaired and works better than new, and I could always go back to the 5.25 drive again. Oh, I have a 3.5" drive ad well, which I can connext by swapping out the 5.25.

There seems to be no shortage of 3" disks (second hand) on ebay, and ALL the ones I have work fine. The drive itself is more likely to be a problem, and not just the drive band. But, they CAN be repaired, a wizard on the CPC forum repaired mine - the stepper motor had died and needed to be rebuilt internally!

Geoff

GeoffB17
July 8th, 2017, 07:57 AM
Chuck - yes plaes, do post the boot sector you're referring to. I can soon do the comparison, and spot the change.

geoff

GeoffB17
July 8th, 2017, 08:22 AM
Another point for OP.

I've never seed the GoTec device, - apart from pictures - so I'm not 100% clear about it, but my understanding if that it connects like a normal drive (but you may need to do something to the system generally). The device uses a SD card, and on that card you create a number (quite a large number ?) of virtual floppy images (.DSK files). This is often perfectly fine if you use a lot of games, etc, and you're dealing with normal floppy disk sizes. BUT, the images are bound by the normal floppy sizes, and I suspect that the maximum is 730k although you maybe can get to near 800k? This is NOT a big help if you play with data files, etc. This is where JonB's device becomes MORE valuable, as now you can manipulate files up to 8Mb. And multiple files on different drives, whereas I suspect the GoTec device has one virtual disk loaded at a time.

Check those things out - I could be off-line regarding the GoTec?

Geoff

Chuck(G)
July 8th, 2017, 08:43 AM
No, you're right on the Gotek--it's basically a drop-in for a single drive. You can have lots of images on your USB flash stick, but it's still just a single drive in a floppy slot. OTOH, it's a simple mechanical fitment--no software changes needed. Note that you need the "double density" 720K version of the Gotek, not the PC "high density" version.

That reminds me--here's the IMD image of the 720K boot disk (https://app.box.com/s/nvvoxizo4j40q9jg2lkzt150kkwbrcwh) that I use on my 8512. Enjoy!

GeoffB17
July 8th, 2017, 09:44 AM
Thanks.

Just had a quick look inside the image, and I note it uses J29CPM3.EMS, which is a PCW9512 system version, and which supports a 720k A: by default. So not sure what any tweak to the boot sector would be needed for?

That version of the system works OK on my 8256 mind you. I also use this version in the Joyce emulator, as it supports the FID file to allow the use of HD (literal and virtual).

Maybe when I used this version, I had to tweak the boot sector the system so that the XDPB was set for a SSSD disk rather than the default DSDD disk.

I'll run your image to a 3.5" disk anyway, just for interest.

Geoff

Chuck(G)
July 8th, 2017, 09:51 AM
IIRC (it's been years), that when I used the "vanilla" 8512 CP/M boot, the system refused to use the second side of the floppy and erred out in the boot. I compared the boot sector with an 8256 and found that they differed in a single byte.

At least that's what I recall--my wetware seems to be drying out nowadays.

GeoffB17
July 8th, 2017, 10:33 AM
Yes, that makes sense. The image you submitted is really for a 9512, which uses a DSDD boot disk as A:. If you try to boot from this disk on an 8512, which expects a SSSD A:, then you'll have the problem you describe. If you compare the boot sectors, there may well be the one byte difference (I think there OUGHT to be more than 1 byte difference, mind you. maybe 2 or three). There would have been no point in changing those bytes, as the system would NOT be able to read the disk, as the disk contains data running over two sides, and the 8512 would read the disk as SS and read 1 side only. You could of course read the disk OK in the B: drive of the 8256.

Geoff

GeoffB17
July 9th, 2017, 01:53 PM
Note to Chuck about the 'tweak' to the boot sector.

I've checked the boot sector data (512 bytes) from your disk (image) against the code on my 8256 boot disk.

Really quite different. No way changing one byte could do what you suggest, unless it's something VERY specific to the specific version of Amstrad's CP/M that you had on that disk (J29CPM3.EMS).

The first 16 bytes of the boot sector have the XDPB info, your data differs from my SSSD setup by 5 bytes in that first 16, these differences just relate to the DPB specs for my SSSD disk and the later DSDD disk.

After that, comes the boot code, and this is clearly quite different, although various little pieces do match between the versions, although these pieces are not in the same place (as per byte offset from the start). But note that my sector is that appropriate for the 8256 (and I'd assume the 8512 which also booted from a SSSD floppy). I'd assume that the code on your disk would HAVE to be different as it needs to read a DS disk.

It is however quite possible that you were changing just the first byte, to a 3 if it was not already, OR changing the second byte which may have been a 1 (for the track layout) to an 81 indicating a non-standard disk. Your disk shows an 81 for this second byte, my - again non standard - 5.25" drive also used an 81 here instead of a 1.

But again, such a change may be valid in certain circumstances ONLY. I would not expect the code on your disk to work on my machine, notwithstanding my machine not having a 3.5" drive A:, as your code will be expecting a DS disk, and I'm sure the boot code is not clever enough to adapt to cope with either SS or DS.

Geoff

Chuck(G)
July 9th, 2017, 02:47 PM
No, I suspect not. I've got lots of Amstrad boot disks of various models in my archives--the change was made quite some years ago, so I could be mis-remembering exactly what I did (almost certainly!). I'm sure that I took one of the boot disks, however, and "tweaked" the boot sector.

It's odd, but I haven't been able to give the machine away, even though it's got the full 512KB memory installed and the 3.5" drive adaptation. I think the Joyce was sold in the US through Sears & Roebuck at some point. At any rate, a 120V Joyce must be pretty rare. I'd picked it up for the 3 inch disk drive.

I also remember looking at the floppy controller circuitry and considered adapting it to HD 3.5" floppies. That was when my interest shifted and the Joyce went onto the shelf and has stayed--collecting dust.

GeoffB17
July 9th, 2017, 03:13 PM
I think that the machine was available ONLY via S&R in the USA.

I'm also on the CPC Wiki forum, which includes the PCW machines. There are a number of US members, incl some who have a PCW or have mentioned interest in one. You might check out the forum, join even, and see if you can find a home for the machine you have.

Does the machine you have still have 3" drives?

http://www.cpcwiki.eu/forum

Geoff

Chuck(G)
July 9th, 2017, 03:47 PM
No, the 3" drive lives in a separate drive box hooked to a PC. The PCW came with only a single drive; I've retrofitted a 3.5" DD Teac.

GeoffB17
July 10th, 2017, 05:47 AM
Oh, that's sad.

The 'vintage' crowd may well consider the machine isn't a real PCW any more. Also, the bulk of PCW software that can still be found will come on 3" disk.

Not a problem for folks like - say - me, who is more tech than vintage. I can move software from web onto 3.5" disks fine, I can create formatted disk etc (using 22DISK). Still nothing I could do with anything on a 3" disk.

So you may have a job finding a home for your PCW8256 (I assume that's what it actually was), although someone MAY be able to find a working 3" drive somewhere, maybe ex-CPC type machine, or from an otherwise dead PCW?

best wishes.

Geoff

Chuck(G)
July 10th, 2017, 07:53 AM
Even in their heyday, 3" disks were as common as hen's teeth on this side of the pond. To the point, I have more 3.25" disks than I have 3" ones. So replacing the drive was more a matter of expediency than anything else. Images of 3" disks made with imaging software should be able to be written to 3.5" floppies with no problem.

As far as 22Disk, well, I'm well aware of its capabilities. :)

GeoffB17
July 10th, 2017, 08:22 AM
Aha! My apologies.

YES, I'd missed that point.

A .DSK for a 3" disk can easily be loaded onto a 3.5" disk, ditto regarding an .IMG file. The software doesn't know any difference. As long as the number of T, S, etc match, fine.

Regarding the disks, even over here, the 3.5" ones were easier to get hold of than the 3" ones, and later in the cycle they were much cheaper too (to be fair though, at the time the PCW came out, there was not much difference pricewise). The problem NOW mind you is that you need DSDD disks, and these are more difficult to find after the HD disks became standard. I've got a pile of 3.5" standard disks, maybe you have too. Other folks (less blessed?) might struggle to find them.

Geoff

PS - is this what you call 'thread drift'? ;)

Chuck(G)
July 10th, 2017, 08:56 AM
I've got cartons of 3.5" DSDD new, unused floppies. It's not likely that I'll run out before I take my final curtain call. Not that long ago, I gave away a few hundred used, tested ones for shipping.

Thread drift? Perhaps, but less than in other cases. After all, the question was about replacing the Amstrad floppy drive with a Chinese emulator. So, in the sense of 3" CF drive replacement, still on-topic.

GeoffB17
July 10th, 2017, 09:49 AM
Chinese?

I understood that the GoTek device was made by someone in E Europe. Maybe Poland? Or was it just designed there, and then manufactured in China. Like most things (TOO many things) these days?? I'll look at the website again.

The last time I looked, there was a list of machines (not all computers) that it was KNOWN to work with, the list included certain Amstrad computers, but NOT the PCW. I understand that this does NOT mean that it will NOT work, and I have seen reference to the device being used with the PCW.

Geoff

Chuck(G)
July 10th, 2017, 10:10 AM
Nope, there is/was a distinctly German producer of devices very different from a Gotek, but the Gotek is strictly a Chinese product--even the originator of the firmware is Chinese, a chip producer who originally gave the emulator as a sample reference design, complete with firmware back around 2011, then withdrew the firmware and bitterly complained about the unscrupulous people stealing their designs.

I get my Gotek emulators straight from China. The design is pretty much dated, as it uses an STM32F105 part.

GeoffB17
July 10th, 2017, 02:07 PM
Hmm, maybe I'm mixing up something called HxC, with GoTek?

The HxC, as I understand it, is a device that looks very much like a 3.5" drive, and might even plug in just as if it was. The device then had a slot for a SD card, although there may be variants (CF ?). Driver software for various different machines then enables the creation of xx virtual disks, which are in effect .DSK files each one appearing as a discrete floppy. The unit has a little LED indicating the currently selected .DSK number. The main distributor/mfg seems to be Polish, but COULD be German (or German/Polish ?).

I should check up just what the differences are!

Geoff

Caluser2000
July 10th, 2017, 02:49 PM
https://www.youtube.com/watch?v=taFP1J_lZBI

Chuck(G)
July 10th, 2017, 03:06 PM
Since both the HxC2000 and the Gotek are ARM Cortex M3-based, there's a version of the firmware that works on the Gotek (https://www.vogons.org/viewtopic.php?f=46&t=43416).

JohnElliott
July 11th, 2017, 11:45 PM
To clarify the difference between 8000-series and 9512 boot disks: The sidedness and TPI aren't the issue. An 8512 will happily boot from a 720k drive A: if one happens to be fitted. The difference is the boot sector checksum. On an 8000-series the 8-bit checksum of the boot sector must be 0xFF; on the 9512 it must be 0x01.

If you load a 9512-type EMS file (J2xCPM3.EMS) on an 8000-series, or an 8000-type EMS file (J1xCPM3.EMS) on a 9512, it'll work but won't be able to drive the built-in printer.