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Microdrives

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  Microdrives Hob <linuxajs@gmail.com> - 2019-03-27 07:03 -0700
    Re: Microdrives Volker Bartheld <news2018@bartheld.net> - 2019-03-27 16:44 +0100
      Re: Microdrives Hob <linuxajs@gmail.com> - 2019-03-27 12:23 -0700
        Re: Microdrives Volker Bartheld <news2019@bartheld.net> - 2019-03-28 08:56 +0100
          Re: Microdrives Hob <linuxajs@gmail.com> - 2019-03-28 12:56 -0700
            Re: Microdrives Volker Bartheld <news2018@bartheld.net> - 2019-03-29 15:45 +0100
      Re: Microdrives Hob <linuxajs@gmail.com> - 2019-03-27 12:30 -0700
        Re: Microdrives Volker Bartheld <news2019@bartheld.net> - 2019-03-28 08:59 +0100
      Re: Microdrives jgh@mdfs.net - 2019-04-16 15:44 -0700
        Re: Microdrives Volker Bartheld <news2019@bartheld.net> - 2019-04-17 08:43 +0200
        Re: Microdrives hp <ferd@farkel.net> - 2019-06-11 18:45 -0400
          Re: Microdrives "Chris" <chris.usenet@mail-filter.com> - 2019-06-17 23:30 +0100
            Re: Microdrives Volker Bartheld <news2019@bartheld.net> - 2019-06-19 21:36 +0200

#4733 — Microdrives

Afternoon all.

It's been a rather long time since I posted here - 15 years, give or take.. I hope you're all well :)

I recently dug out my old stuff from the loft, with the idea of salvaging any data that I might have had (source code, I mean, not games). 

I have several (around 15 I think) microdrives, but both of my Interface 1's are refusing to play ball. One combination of IF1 and MD generates a "Microdrive not present" message every time, the other MD just endlessly spins the tape. 

The other IF1 doesn't initialise properly, generating random key presses or resetting the machine.

Anyone got any ideas on if I can do anything to resurrect the hardware side?

Failing that, anyone got a working IF1 + MD that they would be willing to use to get the data off my carts (if it's still on there!) and email to me?

Ta, 

-- 
Hob.

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#4734

Hi!

On Wed, 27 Mar 2019 07:03:04 -0700 (PDT), Hob wrote:
> I have several (around 15 I think) microdrives, but both of my Interface
> 1's are refusing to play ball. One combination of IF1 and MD generates a
> "Microdrive not present" message every time, the other MD just endlessly
> spins the tape. 

Most likely, at least the latter combination works as designed. Just in
case, the IF1/2 and MDV service manuals are available at
https://spectrumforeveryone.com/wp-content/uploads/2017/08/ZX-Interface-1-2-Microdrive-Service-Manual.pdf.

Before attempting any operation on a cartridge, I recommend checking the
felted foam pad that is supposed to press the tape against the drive head.
Chances are, that after 15+ years, that foam might very soon or even
already has disintegrated. You can "re-felt" this by harvesting the old
felt pads and sticking them on with regular 3M double sided adhesive foam
such as the 3M™ Scotchmount 4032 or anything available at your DIY-shop to
mount mirror tiles to a wall that has a comparable thickness.

I found this guide
https://spectrumforeveryone.com/technical/refelt-zx-microdrive-cartridges/
to be unnecessarily complicated. Just get the old felt, remove foam
residues, use new double sided foam stickers cut to fit with a sharp
knife, scalpel or even scissors and put everything back in place with a
good set of (non magnetic) tweezers. You might want to bend back the spring
a little but be careful in order to not rip it out of the case and also
make 100% sure that no adhesive is exposed to the tape because this will
inevitably mean hell breaking loose, the moment you use it.

Then take a cartridge with no valuable data on it and try to reformat it
using FORMAT "m";1;"test" followed by CAT 1 (user manual here:
http://www.sinclair.hu/speccyalista/konyvtar/kezikonyvek/ZXInterface1_Microdrive_Manual.pdf)
to see if everything works. If you get around 85kB out of it, your main
problem might be magnetic print-through.

This especially happens with the BASF Superchrome tapes that were commonly
used in those cartridges and means that magnetic information has been
transferred from one layer of the tape to another one, lowering
signal-to-noise-ratio which the Microdrive's very basic circuits could not
deal with.

If that is the problem, the only remedy is to read the cartridges
"externally", e. g. using the naked hardware to spin the tape but attach
an instrumental amplifier and digital storage scope the the head (2
channels, since it's Stereo), sample a few turns and process the
information on a PC.

That requires knowledge of the data format which can be acquired by
studying the IF-1 ROM disassembly from here:
https://www.tablix.org/~avian/spectrum/rom/if1_1.htm
https://www.tablix.org/~avian/spectrum/rom/if1_2.htm
or reading Gianluca Carri's excellent book "Spectrum Shadow ROM
Disassembly" which used to be available via 
ftp://ftp.worldofspectrum.org/pub/sinclair/books/SpectrumShadowROMDisassembl
but now has disappeared. So better grab the post mortem image from
https://archive.org/download/World_of_Spectrum_June_2017_Mirror/World%20of%20Spectrum%20June%202017%20Mirror.zip/World%20of%20Spectrum%20June%202017%20Mirror/sinclair/books/s/SpectrumShadowROMDisassembly.doc
while it still exists.

If you are sure your cartrdiges, IF-1 and Microdrive work correctly, you
might want to give
http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip
a try and transfer everything to your PC for emulating the content with
Eightyone or any other software that understands the .mdr format initially
invented by Gerton Lunter.

> Failing that, anyone got a working IF1 + MD that they would be willing to
> use to get the data off my carts (if it's still on there!) and email to
> me?

I won't even try data recovery on your cartridges since it quite certainly
can't be done on the original hardware for the reasons explained above.
From the IF-1, bunch of microdrives in various states of disassembly and
~50 cartridges, I would only send any spares to somebody willing to assist
me with the magnetic print-through issue in a constructive, reproducable
way to share with the community. Many have promised, nobody has delivered.

HTH & greets,
Volker

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#4735

On Wednesday, 27 March 2019 15:44:52 UTC, Volker Bartheld  wrote:

> Hi!
> 
> On Wed, 27 Mar 2019 07:03:04 -0700 (PDT), Hob wrote:
> > I have several (around 15 I think) microdrives, but both of my Interface
> > 1's are refusing to play ball. One combination of IF1 and MD generates a
> > "Microdrive not present" message every time, the other MD just endlessly
> > spins the tape. 

I think I should have made that clearer - I have about 15 microdrive *cartridges*, two IF1s and two MD units. 

> Before attempting any operation on a cartridge, I recommend checking the
> felted foam pad that is supposed to press the tape against the drive head.
> Chances are, that after 15+ years, that foam might very soon or even
> already has disintegrated. You can "re-felt" this by harvesting the old
> felt pads and sticking them on with regular 3M double sided adhesive foam
> such as the 3M™ Scotchmount 4032 or anything available at your DIY-shop to
> mount mirror tiles to a wall that has a comparable thickness.

OK, I'll give that a shot on one of the carts. The other (minor!) issue is that the keyboards on both Spectrums have died, so I've bodged together a "keyboard" involving threading the individual strands of solid Cat5 cable through holes drilled into the case and soldering the other ends to the PCB. Pretty it isn't. 

> This especially happens with the BASF Superchrome tapes that were commonly
> used in those cartridges and means that magnetic information has been
> transferred from one layer of the tape to another one, lowering
> signal-to-noise-ratio which the Microdrive's very basic circuits could not
> deal with.

I've read about that, didn't know it was a thing until a couple of days ago. 

> If that is the problem, the only remedy is to read the cartridges
> "externally", e. g. using the naked hardware to spin the tape but attach
> an instrumental amplifier and digital storage scope the the head (2
> channels, since it's Stereo), sample a few turns and process the
> information on a PC.

This piques my technical curiosity - can you explains more about this theory? I'm intrigued to know more. 

> If you are sure your cartrdiges, IF-1 and Microdrive work correctly, you
> might want to give

That, I am not at all sure. I suspect the ULA on one of them (given the endless loop spinning) and something more basic on the other. I have wondered whether dry joints or other similar hardware type deterioration might be responsible.

I can't remember when I packed them away, but it would have in the region of 1987 - 1988, when I got my Atari ST..

Thanks for your reply. 

-- 
Hob

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#4737

Hi!

On Wed, 27 Mar 2019 12:23:16 -0700 (PDT), Hob wrote:
> On Wednesday, 27 March 2019 15:44:52 UTC, Volker Bartheld  wrote:
>> [magnetic print-through] especially happens with the BASF Superchrome
>> tapes that were commonly used in those cartridges and means that
>> magnetic information has been transferred from one layer of the tape to
>> another one, lowering signal-to-noise-ratio which the Microdrive's very
>> basic circuits could not deal with. If that is the problem, the only
>> remedy is to read the cartridges "externally" [...] attach an
>> instrumental amplifier and digital storage scope the the head (2
>> channels, since it's Stereo), sample a few turns and process the
>> information on a PC.

> This piques my technical curiosity - can you explains more about this
> theory? I'm intrigued to know more. 

Print-through is a fairly trivial process. Chrome - Cr(IV)-Oxide aka. CrO2
- is ferromagnetic and can carry quite high magnetic field strenghts and
has a relatively high hysteresis, at least in comparison with iron. In
terms of magnetic data storage, CrO2 is still considered a pretty "soft"
magnetic material in comparison with modern stuff (e. g. CoCrPt) which is
used in nowadays' hard disk drives. "Soft" means that it does not take
much to change magnetization and as an effect, the magnetic information
("bits") broadens by itself, occupying a larger area and nearby bits are
literally smeared. Also, the magnetic information from one layer of tape
can propagate to another layer of tape in areas where the tape sits on its
spool(s), especially, when the tape is very thin which was the case for
microdrive cartridges.

As a result you get at least a fraction of the magnetization originating
from one bit to the bits nearby and on multiples of the spool
circumference. Just think of a superposition of individual square waves
(OK, "square-ish" waves) with different amplitudes, where the wave with
the highest amplitude is the original one and ontop comes a wave with -
say - 25% of that amplitude but with some displacement added.

If you run the result through a simple Schmitt Trigger, you get "false"
zero crossings and such zero crossings typically indicate bits. More
details here:
https://en.wikipedia.org/wiki/Magnetic_storage#Digital_recording
Since the Microdrive's electronics is pretty limited, there is no way to
eliminate those false zero crossings and the checksum errors they generate.
As a result, the file and file system is corrupt.

As soon as you sample the analog signals from the drive head(s) with enough
resolution, you could detect the ghost waveform that was printed through,
eliminate false zero crossings and reconstruct the original data. At least
in theory.

My rough calculation of the required bandwidth came up with the following:
7 seconds per spin, approximately 100kB capacity, sector length is 542
bytes, 512 are actually usable for storage (rest is administrative
informormation for the file system). So we have around 867200 Bit in 7s.
Since the MDV has a Stereo head, we have halve the Bit rate, so the
frequency is ~62kHz. You would at least need 4x oversampling for a decent
reconstruction, that means 250kHz per channel. So this does not work with
the ADC of an Arduino, simple embedded solutions (=replacing the entire
MDV electronics, ULA, etc. by an emulation) are out.

Digital scopes to enter the game, probably even the quite cheap 100MHz
generation will do if it can store ~10s at 1MHz, which is pretty rarely
the case. These might do:
https://www.rigolna.com/products/digital-oscilloscopes/1000/
but they are not exactly cheap.

That's about everything I know about this topic.

>> If you are sure your cartridges, IF-1 and Microdrive work correctly, you
>> might want to give [mdv2img a try]

> That, I am not at all sure. I suspect the ULA on one of them (given the
> endless loop spinning) and something more basic on the other.

I'm not sure if this "endless" spinning could also be caused by data
integrity issues. E. g. if there are some read errors and the MDV tries to
read the data again and again. I don't remember, if there's a maximum loop
counter coded in the IF-1's firmware, so it might just _look_ as if the MDV
was spinning for ever. By reformatting a cartridge, you can eliminate that
problem.

> I have wondered whether dry joints or other similar hardware type
> deterioration might be responsible. I can't remember when I packed them
> away, but it would have in the region of 1987 - 1988

Same here. My findings were, that - once refelted and reformatted - those
cartridges work like a charm, more than 30 years after they were built. But
the original data is inaccessible for me in the current situation.

Greets,
Volker

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#4739

On Thursday, 28 March 2019 07:56:15 UTC, Volker Bartheld  wrote:

> My rough calculation of the required bandwidth came up with the following:
> 7 seconds per spin, approximately 100kB capacity, sector length is 542
> bytes, 512 are actually usable for storage (rest is administrative
> informormation for the file system). So we have around 867200 Bit in 7s.
> Since the MDV has a Stereo head, we have halve the Bit rate, so the
> frequency is ~62kHz. You would at least need 4x oversampling for a decent
> reconstruction, that means 250kHz per channel. So this does not work with
> the ADC of an Arduino, simple embedded solutions (=replacing the entire
> MDV electronics, ULA, etc. by an emulation) are out.

I would imagine that the data reproduction is not identical with each spin in this case, so would sampling several times produce examples that are inequal, but might be overlaid with each other to produce a map of accurate bytes against inaccurate bytes?

Might getting the data off - in any form - mean it could then be subject to much more powerful processing of today's computers?

How about a USB cable that would be allow software to operate the microdrive?

I might be talking absolute cobblers though. 

> I'm not sure if this "endless" spinning could also be caused by data
> integrity issues. E. g. if there are some read errors and the MDV tries to
> read the data again and again. I don't remember, if there's a maximum loop
> counter coded in the IF-1's firmware, so it might just _look_ as if the MDV
> was spinning for ever. By reformatting a cartridge, you can eliminate that
> problem.

Yeah, I wondered that too. But whilst some cartridges are labelled ("Elite", "Tasword Two - Do Not Overwrite") such that the contents might be considered expendable, I'm not 100% sure. I was a little lax back in the day with labelling - of course, I just knew which cart had what on it. 

I'm mostly interested in source code that I might have on them - I imagine there might only be one or two out of the 15 or so that have (had) anything on them. The rest, I'm just curious about. 

-- 
Hob

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#4740

On Thu, 28 Mar 2019 12:56:49 -0700 (PDT), Hob wrote:
> On Thursday, 28 March 2019 07:56:15 UTC, Volker Bartheld  wrote:
>> My rough calculation of the required bandwidth came up with the
>> following: [...] You would at least need 4x oversampling for a decent
>> reconstruction, that means 250kHz per channel [of a 2-channel scope].
>> So this does not work with the ADC of an Arduino, simple embedded
>> solutions (=replacing the entire MDV electronics, ULA, etc. by an
>> emulation) are out.

> I would imagine that the data reproduction is not identical with each
> spin in this case, so would sampling several times produce examples that
> are inequal, but might be overlaid with each other to produce a map of
> accurate bytes against inaccurate bytes?

I tried bitwise average with Mdv2Img's PC code by sampling more spins of
the tape and running it through the CBitwiseAverage template class. This
didn't change much, flipped bits mostly stayed flipped bits. Also keep in
mind that header checksum errors (HDCHK) mean, that you can't even be sure
that your are reading the correct sector.

No, there was no external hardware (sampling scopes) involved, just the
cartridge, Microdrive, its ULA, the IF-1, its ULA, Mdv2Img and some PC
magic.

> Might getting the data off - in any form - mean it could then be subject
> to much more powerful processing of today's computers?

It didn't. Of course we could use forensic methods to somehow "guess" what
the data could have been, but I was not able to spend more time on this
back then. You should definitely download
http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip and at
least read Mdv2Img.txt to understand the status quo.

> How about a USB cable that would be allow software to operate the
> microdrive?

That would mean placing an Arduino or other uC inside the MDV to replace
the original hardware. The Arduino's ADC is way too slow, so you need a
two-channel ADC shield that can run at 1MHz and above. You then need to
transfer the bitstream to the PC via USB, 1MB/s (given that 8 Bits
sampling depth are adequate) is within the specs of USB2.0, I don't know
if the Arduino can do that, however.

An alternative could be an ARM Cortex architecture which is more powerful.
Feel free to design and prototype something with KiCad that will fit the
Microdrive's interface points (drive motor, drive head, LED, Write protect
tab, etc.) so it can be hooked directly to a PC.

>> I'm not sure if this "endless" spinning could also be caused by data
>> integrity issues.

> Yeah, I wondered that too. But whilst some cartridges are labelled
> ("Elite", "Tasword Two - Do Not Overwrite") such that the contents might
> be considered expendable

Jup. Every piece of software that has ever been commercially sold for the
Sinclair ZX Spectrum exists as perfect image meanwhile. No need to waste
your time there. You'd only want to preserve your personal stuff - if it's
worth it.

> I'm mostly interested in source code that I might have on them - I
> imagine there might only be one or two out of the 15 or so that have
> (had) anything on them. The rest, I'm just curious about.

So you could use one cartridge as a donor, where you are 99.9999% sure that
it contains no invaluable/irreplaceable data and try if you can
successfully reformat and use it. If that succeeds, there's proof that you
have hardware that works and can give Mdv2Img a try. You'll probably find
out, that your Cartridges suffer the magnetic print through issue, too and
would need to come up with an idea on how to externally sample the
information.

HTH & greets,
Volker

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#4736

On Wednesday, 27 March 2019 15:44:52 UTC, Volker Bartheld  wrote:

> or reading Gianluca Carri's excellent book "Spectrum Shadow ROM
> Disassembly" which used to be available via 

I don't actually need to download these - I have a hardcopy of both this, and the Complete ROM Disassembly - though I did download them for convenience :-)

-- 
Hob

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#4738

On Wed, 27 Mar 2019 12:30:59 -0700 (PDT), Hob wrote:
> On Wednesday, 27 March 2019 15:44:52 UTC, Volker Bartheld  wrote:
>> or reading Gianluca Carri's excellent book "Spectrum Shadow ROM
>> Disassembly" which used to be available via 
> I don't actually need to download these - I have a hardcopy of both this,
> and the Complete ROM Disassembly

Probably everyone who was decently into software development bought these,
back then. Together with Rodnay Zak's "Programming the Z80" which I can
highly recommend to anyone wanting to learn machine code development or
understand what makes a CPU tick. IIRC that book is also available online.

> - though I did download them for convenience :-)

Sure. Same here. You never know...

Greets,
Volker

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#4742

Volker Bartheld wrote:
> If you are sure your cartrdiges, IF-1 and Microdrive work correctly, you
> might want to give
> http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip

Warning: Infected with Win32:Malware-gen

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#4743

On Tue, 16 Apr 2019 15:44:22 -0700 (PDT), jgh@mdfs.net wrote:
> Volker Bartheld wrote:
>> If you are sure your cartrdiges, IF-1 and Microdrive work correctly, you
>> might want to give
>> http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip
> Warning: Infected with Win32:Malware-gen

It isn't. False positive. Avast sucks. Trust me on that.

MD5 Sums:
ad0b449e7768786d9c18c808fa8ea31e *bas2tap.exe
31eb5c369132026f052063cea10aeeb1 *BinTap.exe
d2e5115a4c11b1fc6f6f3da135d30101 *mdv2img.exe

All binaries - including bas2tap.exe which is the offending file - built
with MSVS 2012 from included sources.

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#4755

On 4/16/2019 6:44 PM, jgh@mdfs.net wrote:
> Volker Bartheld wrote:
>> If you are sure your cartrdiges, IF-1 and Microdrive work correctly, you
>> might want to give
>> http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip
>
> Warning: Infected with Win32:Malware-gen
>


Humm, Interesting it is Jun 11 and I too got this flag after clicking
the above referenced link

So,  I went one step at a time

www.worldofspectrum.org

then found and clicked	pub

then found and clicked	sinclair

then found and clicked	tools

then found and clicked	pc

then found and clicked	mdv2img.zip

That Failed to download   'The connection was reset'  was the indication
I got  Rather then 'infected'

Your experience might differ

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#4756

On Tue, 11 Jun 2019 18:45:07 -0400 da kidz on comp.sys.sinclair were rappin'
to MC hp:

> On 4/16/2019 6:44 PM, jgh@mdfs.net wrote:
> > Volker Bartheld wrote:
> >> If you are sure your cartrdiges, IF-1 and Microdrive work correctly, you
> >> might want to give
> >> http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip
> >
> > Warning: Infected with Win32:Malware-gen
> >
> 
> 
> Humm, Interesting it is Jun 11 and I too got this flag after clicking
> the above referenced link
> [...]
> That Failed to download   'The connection was reset'  was the indication
> I got  Rather then 'infected'
> 
> Your experience might differ
> 

Virustotal seems to think it's fine.
https://www.virustotal.com/old-browsers/url/e0994387f30c4a7193fa7d4848dc2b0852848f354d04abdf216e450a57866ec4

Chris


-- 
Tw: @AwakeInBeds (Get with the future, people, it's 1987!)
+---------------------------------------------+
| Unsatisfactory Software    @_unsatisfactory |
|   http://www.unsatisfactorysoftware.co.uk   |
| Your Sinclair: A Celebration  @YourSinclair |
+-- http://www.yoursinclair.co.uk ------------+

DISCLAIMER: I may be making all this stuff up again.

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#4757

On 17 Jun 2019 23:30:30 +0100, Chris wrote:
> On Tue, 11 Jun 2019 18:45:07 -0400 da kidz on comp.sys.sinclair were rappin'
> to MC hp:
>> On 4/16/2019 6:44 PM, jgh@mdfs.net wrote:
>>> Volker Bartheld wrote:
>>>> http://www.worldofspectrum.org/pub/sinclair/tools/pc/mdv2img.zip
>>> Warning: Infected with Win32:Malware-gen
>> Humm, Interesting it is Jun 11 and I too got this flag
> Virustotal seems to think it's fine.
> https://www.virustotal.com/old-browsers/url/e0994387f30c4a7193fa7d4848dc2b0852848f354d04abdf216e450a57866ec4

Folks, it's just a fricking .zip file. Grab it and check yourself. Just in
case courious minds want to know - this it the content:

mdv2img.zip
¦   bas2tap.c
¦   bas2tap.vcproj
¦   Bintap.cpp
¦   BINTAP.H
¦   BINTAP.TXT
¦   BinTap.vcproj
¦   debug.cpp
¦   debug.h
¦   errx.h
¦   getargs.cpp
¦   getargs.h
¦   helper.h
¦   mdv2img.bas
¦   mdv2img.bat
¦   mdv2img.cpp
¦   mdv2img.h
¦   mdv2img.sln
¦   Mdv2Img.txt
¦   mdv2img.vcproj
¦   mdv2img.z8a
¦   recycler.cpp
¦   recycler.z8a
¦   tstdlibs.h
¦
+---Doc
¦       BINTAP.TXT
¦       Config_1.png
¦       Config_2.png
¦       Config_3.png
¦       Config_4.png
¦       MC_Loader.png
¦       Mdv2Img.txt
¦       Operation.png
¦
+---Release
¦       bas2tap.exe
¦       BinTap.exe
¦       mdv2img.bin
¦       mdv2img.exe
¦       MDV2IMG.SNP
¦       mdv2img.tap
¦
+---Test_Data
        Games_01.bin
        Games_01.bin.log
        Games_01.mdr
        test_00.bin
        test_00.bin.log
        test_00.mdr

So, if you've got access to MSVC2012 or better, alternatively GCC and are
willing to spend plenty of leisure time, just ditch the evil \Release
folder that I have prepared for the ones who don't suffer an acute case of
paranoia and compile their Linux kernels themselves.

'coz the rest is plain boring text files, Z80 assembler and some C++ source
code pr0n.

Since you probably don't have access to a working Speccy with Interface 1,
Microdrive and some cartridges that didn't have their content eaten away
by the dreaded magnetic print through issue and are willing to solder a
RS232 cable or want to contribute some insights on how to harvest raw data
from the drive head with an instrumental amplifier and digital scope, I'm
wasting my time with futile explanations anyhow.

That being said: Have fun. Or just leave it alone.

Cheers,
Volker

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