[HH] Burn custom art on a DVD

[Greg London]

I did asic design on CD and DVD burners for a number of years
but it was years ago and before lightscribe was an option,
so I can't really compare burning data to a disc to lightscribe.

I don't know as much about the physical process
but I don't know what is meant by "test grooves". My understanding
is that burning a cd doesn't actually put grooves on it like
a vinyl record but rather turns the transparent polycarbonate
dark so that it does not reflect light from the aluminum disk
underneath.

So that would be the first issue/question, whether the physical
process will actually do what they want to do.

The second question is one of synchronization between the
laser and the spinning disk. I worked on the CD read section
of the chip, taking a stream of high speed data, de-interleaving
it and running it through a 10b8 error recovery block, so
I'm not as familiar with DVD's as CD's but I'm not sure that
there is any sort of "index hole" marker on the CD to physically
align the head back to the same spot.  audio CD's are one big,
long spiral of data starting from the inside and working out.
DVD tracks are concentric circles with sectors and whatnot.
But  I don't know of there is any kind of index hole so that you
could put down a stream of 1's on one track, move the head out,
and then put another stream right alongside the previous stream.

If the only requirement is to create a specific pattern
on a single track, it should be possible. But if you
want to lay down data on different tracks and have them
be physically aligned with each other, I'm not sure
that's even possible.

The other bit of weirdness is that the RPM changes as you move
the head to different tracks. The goal is to achieve constant
linear speed over the track which gives you constant data
rates coming off the head.

Back in the day, audio CD drives were built with only very
small data buffers in silicon, usually just enough to perform
de-interleaving, 10b8 error correction on one block (48 bytes)
while receiving the next block. So, as the head spiraled further
out from the center, the disk would be spun at slower and slower
rpm's.

I think DVD's generally follow this Constant Linear Velocity
approach, which means you've got more data in a track as you
move further out from the center. This doesn't make it impossible
but if you want a couple of "test grooves" to lay side by side
then they'll default to being the same linear length, not the
same arc of rotation.

Lastly, based on how our chips worked, I can't even imagine
getting direct control of the heads through software.
Maybe other chips let you have more direct control, but
there is so much data flying that most of it is automatic.

By the time the serial data comes off the disc, its already
run through serial de-interleaving, 10b8 error correction,
and a bunch of other hardware blocks before the software
ever sees it. prior to that point, its just moving too fast
for software to keep up.

I think the best you could hope for is to work within the
existing DVD format and simply try to control what track
the head is on and then give it a block of data to write.

And even then I don't think there is any way to align one
track to the track next to it.

Anyway, this is all very fuzzy recollections of stuff
I worked on a long, long time ago, in a galaxy far away.

Someone more current might be able to do it no problem.

Greg






> My son-in-law got this from his boss. I assume he wants to burn art into a
> lightscribe DVD. The place of business is in East Cambridge, his wife used
> to live 2 doors away from me while she was married to someone else.
>
> -------
> The objective is to burn many grooves on the DVD that will NOT be holding
> any data or pictures.  Imagine that you have a pattern template that you
> have drawn using some drawing tool and you want to burn  "grooves" on the
> DVD using the DVD writing head.  There are "artist" specific software that
> do this however, they are not precise enough for my friend's purposes
> which is to create "test grooves" to test various organic compounds using
> low voltage electricity.
>
> So I guess what I am looking for is someone that can write a firm ware to
> move the head AND provide a "crude" user interface to draw simple straight
> lines (for the template) and use the DVD writer to etch the grooves along
> the lines created by the user.
>
> Here is the device:  HP CDDVDW TS-L633N 0300 195 (LightScribe)
>
> They will pay good money for an electrical engineer that can do that.
>
> I hope this is helpful.  This will not be used in any commercial capacity.
>  It is only for testing in a laboratory environment.  Thanks.
> -------
>
> --
> Jerry Feldman <gaf at blu.org>
> Boston Linux and Unix
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