*BSD News Article 18252


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From: guest@nemesis.UUCP
Date: 11 Jul 93 16:29 CDT
Newsgroups: comp.os.386bsd.questions
Subject: Re: mitsumi CD-ROM drive
Message-ID: <-21066809@nemesis>
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Nf-From: nemesis.UUCP!guest    Jul 11 16:29:00 1993
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[0]>	Is there a drivre for the Mitsumi CD-ROM drive and if so where can I
[0]>	get one, or can someone mail me one??

[1]The driver is being worked on.  Holger Veit is working on the data part,
[1]and I'm working on the audio part.  My code should be done shortly
[1](probably over the weekend).  I don't know how long Holger will take,
[1]but I don't expect it to be very long as he was working on DMA transfers
[1]last I heard.
[1]
[1]After that, we'll probably want to test it for a bit.  I don't know if
[1]Holger has anyone lined up for alpha/beta testing, but I'll see about
[1]adding your name to the list.

Beware.  Speaking as someone who had access to actual Mitsumi source code and
drive specifications, I cannot advise anyone to seriously consider any of
Mitsumi's current or earlier CD-ROM drive offerings.  By this I mean the
clamshell version (push-click-pull tray, raise lid, either 850 or 390 msec
versions), or the motorized tray version (seen with BSR plate from DAK or
in Tandy VIS system, 1,300 msec (yes, 1,300 msec!)).  All of these drives
are frequently seen with various brand-name labels on them, including
Acer, BSR and Tandy, and can be found for $175 to $299, depending on the shop.

The Mitsumi MTBF (mean time between failure) on these drives is listed
at under 9000 hours, well below what you would find on any other
drive out there.  There are several reasons for this low MTBF:
(1) Brush-style DC motor on optic transport (some models also have one on
the spindle too, which must be equipped with a spin-down-when-idle function
to avoid burning out too quickly)  and, (2) rubber band drive belt for
optical pick-up transport on some models, a nylon wormgear on others.  

The clamshell model can also damage discs if the door is opened too
quickly and the disc is still spinning.  This should be impossible with
the motorized tray, but every now and then it will open the tray with
the disc still spinning and scraping around the tray.

There are also numerous firmware revisions, none of them fix all the bugs.
Command and functions appear in one and disappear (or quit working in the
next.)   Finding a single driver that works on every iteration is probably 
impossible.  Mitsumi has not managed that yet for DOS.

The DOS driver(s) they provide is a massive joke, obviously written by someone
who had never written 80x86 assembly before.  Did you know you must always
CLC before doing an ADD?  And AX is the only register that conditional
operations can be done in?  Whoever wrote that code thought so.

The drive provides R-W subcodes (nice feature), but a massive amount of code
is required to de-interleave, error correct, and get around bugs in the
firmware.

The drive interface is also pretty efficient, according to the Microsoft
benchmark.  The motoroized drive had 8% CPU overhead on a 12MHz 286 system,
while a popular drive from another vendor had 30% CPU overhead on a 25MHz
486SX computer.  The difference is mainly DMA vs non-DMA, with many drives
being non-DMA.  Both Mitsumi models can fo 150K/sec streaming data
transfers, but the motorized version is highly sensitive to ground loops
between data, power cables and the frame.  The presence of a ground loop
can drop the data rate to as low as 23K/sec.

There is also a bug in the Mitsumi firmware (ALL VERSIONS to my knowledge)
that if you have a mixed-mode disc (track 1 data, track 2-n audio) and
you attempt to read a file or block within about 40K of the end of
Track 1, it will get read errors and start playing music out the D-to-A.
We had to master all our disc with a large file (or oversized partition )
that was never accessed in the last part of track 1 to avoid this problem.

If its just a HS/ISO disc, the dead space is still required or else the
drive will get read errors trying to read-ahead into the lead-out area.

Finally, at last report, Mitsumi still doesn't have a drive that would do
multi-session photo CD correctly.   Tandy gave up and stopped using Mitsumi
drives last in Spring 1992 for computers and switched to a LMS (Philips
in America) drive.

Bottom line, you pay for what you get.   :-(