Switching CD images without external tool (using BlueSCSI with a DTS 6D)

[nehalem501]

Hello,
I would like to use my BlueSCSI with less mainstream hardware: a DTS 6D.
This device is used in movie theaters to read a digital soundtrack from CD-ROMs when projecting a 35mm film. Synchronization is done using a time code that is present on the film.

It is read using a special reader mounted on the film projector and data is fed through some kind of serial connection. Each film (or trailer, logo, ad, ...) has a unique ID on its time code track that the device uses to find the appropriate file on the inserted CD-ROMs.

The device itself is a custom-made DOS PC with some special ISA cards and SCSI optical drives (some units have IDE drives, but these are connected through IDE-SCSI converter boards to the motherboard anyway). Think AT stuff with either a 386 or 486 and 1MB of RAM.

Here is a video of it booting up after putting a VGA card into one of the ISA slots for those curious.

First, the good news is that the current BlueSCSI firmware works with this device. With an appropriate ISO image assigned to the SCSI ID of the optical drive it is replacing, it can read the disk.

The problem is that because CDs are not big enough to fit the data for 5 channel audio even with their compression codec, a full length movie needs 2 discs. And trailers were generally using a 3rd disc (this is why the device has 3 drives, so it could be operated unattended).

I would like to avoid replacing all 3 optical disk readers with BlueSCSIs and figure out a way to do everything with only one. The problem is that the DTS device is not meant to be operated with a keyboard and a screen. If you didn't put one yourself, it doesn't even have a VGA card (and AT-PS/2 adapters and ISA VGA cards are not the kind of thing people operating these devices usually have lying around). From the point of view of the user, this is a glorified CD player where the only user input possible, apart from turning it on or off, is inserting or ejecting disks with the optical drives.

I saw that it is possible to switch CD images with some graphical apps for Mac or other OSes. Is it possible to do it directly on the BlueSCSI with a button or something?
I could build a PCB with buttons and a small OLED screen to list and choose the images, but how could it communicate with the BlueSCSI? Are there some unused pins left on the Pi Pico?

[erichelgeson]

Thanks for the report on a working system! Currently no there is no button (but I do have code to do this, i really just need to wrap it up, maybe this will be the push) - I am also working on a web interface as well so you can switch just via your phone's browser or computer.

But maybe there is an easier option - BlueSCSI can emulate up to 7 devices - so it can emulate all 3 CDROM drives just like you have shown. For example name the files CD0 - Movie part1.iso, CD1 - Movie part2.iso and CD3 - trailers.iso - all 3 would be active at the same time on SCSI ID's 0, 1, and 3 (as an example)

HTH let us know how it goes!

[stinkerton18]

Do you know, or have you investigated, whether the software for fetching/playing the sound off the CDs is using Unit Numbers (SCSI ID), volume name, or drive letter to map the incoming unique ID/play request to the disc in the drive to play?

Off the cuff I would imagine the BlueSCSI presented devices will have to be the same as the original hardware CDROM drives (IE can't mix/match). DOS doesn't really have a "shortcut" or symbolic link ability in file/drive paths.

[nehalem501]

You mean how it identifies if the disc is for the film ID coming from the time code? It has nothing to do with drive IDs. It's a simple 16-bit unsigned integer contained in the header of the audio files on the disc. See here.

[stinkerton18]

So the software agent is just blind scanning all the disks to find one that has a file with the desired 16-integer? The reason I'm asking is the case has each drive labeled as A, B, and C. So to me, that implies that "Trailer disc goes in A." or some other sort of specific drive A/B/C is used for trailer disc, Drive B is for 1st half of movie, Drive C is for second half.

If it doesn't matter what disc goes in what drive, then yeah the software/TSR agent must be doing some kind of scan/indexing of a disc when the drive is closed and storing that info into a lookup table in memory. Thus, it wouldn't matter what the IDs are of the BlueSCSI drives.

[nehalem501]

Well that's kind of the idea. The DTS discs contain an EXE and the audio files. I don't know if the device uses the EXE to check the metadata or if it uses its own program for this. (I will need to hook it up with an actual 35mm projector to understand more how this works). But if I remember well, the order in which you put the discs in the 3 optical drives is not important, it figures out what it needs to play by itself.

There also a newer version of this device called the DTS XD10 that uses modern hardware and runs Linux which copies the data of the discs to its hard drive and creates additional files to store the metadata to know which file to play when it receives a valid time code signal. This newer device doesn't need to use the EXE contained on the CDs for that.

[stinkerton18]

Ahhh! If there's an EXE with the disc, that's probably the TSR that's looking for/responding to the time stamps and paying the files on its disc. Knowing it doesn't matter what disc is in what drive makes it a lot easier to add a BlueSCSI and test it out.