🚀 go-pugleaf

Carsten Schultz writes
| BrianW@SoundS.WA.com (Brian Willoughby) writes:
| ..
| > The differences between audio and data CDs are a little more complicated  
| > than that.  The simplest way I can think of explaining it is that audio CDs  
| > are like  
| [what seems a fine description of CD format]
| 
| Sorry, but I think, this copy protection bit stuff (actually two bits, I  
| think) is really true. Isn't there somethind like CDaudio in the  
| fileystems directory? BTW, does anybody have a not copyprotected audio CD?

The very last paragraph of my previous posting acknowledges the copy protection  
bit, but that is immaterial to the original problem/question of how to get the  
digital audio data into the NeXT - a problem that I would like to see solved.   
I authored that post while sitting in front of a copy of the N.V. Phillips and  
Sony Corporation specifications for CD Digital Audio, CD-ROM, and CD  
Interactive.

I can only speculate about the extent of the support in the CDaudio filesystem  
code, but I can say for a fact that the CPU-541 (the drive used in NeXT's  
CD-ROM drive) will not send any digital audio data to the NeXT through the SCSI  
interface.  I also happen to have a copy of the Sony CDU-541/CDU-6211 SCSI  
Interface Manual and there is no support for reading Digital Audio data.  The  
MODE SELECT command only supports block lengths of 256, 512, 1024, 2048 (CD-ROM  
Mode 1), 2336 (CD-ROM Mode 2), & 2340 bytes of user data.  In order to read  
Digital Audio data into the NeXT, the block size would need to be set to 2352  
bytes, but the manual states that any size not in their list is considered an  
ILLEGAL REQUEST and results in an error.  Perhaps the ROM firmware in the NeXT  
CD could be rewritten to support the transfer of the full block, but the driver  
on the NeXT would probably need to be rewritten as well, and I don't know how  
to do that.

I would suppose that the CDaudio filesystem exists merely to allow the NeXT  
operating system to be happy about an audio CD which is inserted in a drive and  
to allow seeking and playback via the audio-specific SCSI commands.  The  
existence of the CDaudio filesystem does not imply that the actual digital  
audio information can be transferred over the SCSI bus.
-- 
Brian Willoughby	Software Design Engineer, BSEE NCSU
BrianW@SoundS.WA.com	Sound Consulting and Signal Processing Software
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