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From: mattd@Apple.COM (Matt Deatherage)
Newsgroups: comp.sys.apple2
Subject: Re: Two questions
Message-ID: <44644@apple.Apple.COM>
Date: 9 Sep 90 19:04:26 GMT
References: <1990Sep8.073212.2278@wrkof.incom.de>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 54

In article <1990Sep8.073212.2278@wrkof.incom.de> spock@wrkof.incom.de (Martin Georg) writes:
>   
>1) One friend tried to use a Laser 800KB Unidisk-compatible disk drive
>connected via the UCD on his IIgs under GS/OS (System 5.02).  On boot-
>up, the System popped up a message stating something like: Unidisk re-
>quires a driver. Please install driver and reboot system". He did that
>and rebooted but the message still popped up. Of course the driver was
>turn on (active) using the Finder's IconInfo dialog. 
>Does someone use this configuration on his IIgs??? Is there a special
>driver needed (I think the system will use a generated driver if no
>special driver is available...). Is there a special Laser 3.5"-driver
>available???
>  
This is partly Central Point's fault and partly Apple's fault, and partly the
fault of copy-protected programs.

For every SmartPort device there is a type and a subtype.  The type identifies
the generic type of device connected (such as "3.5 disk" or "SCSI hard disk").
Unfortunately, there's no place in the definition to identify the *specific*
kind of device (such as "Unidisk 3.5" or "Apple 3.5 drive").  What some people
did, encouraged by faulty Apple documentation, is look at the "subtype" byte
which is really a byte of flags.  Bit 7 is set if the device supports Extended
SmartPort, bit 6 is set if the device supports disk-switched errors, etc.

You can probably see this coming - you can't use the same byte as an ID byte
and as a byte of flags.  For example, the built-in drive in the IIc Plus has
characteritics that make its subtype be $00.  That's the same as the documented
subtype of the Unidisk, but the IIc Plus drive does not support the Unidisk
device-specific calls.

Central Point deliberately chose to return subtype $C0 for Apple 3.5 drives 
attached to the UDC so copy-protected programs looking for the $C0 subtype
byte would run correctly.  Unfortunately, their interface doesn't support the
Extended SmartPort protocol one of those bits says is present.  When GS/OS
tries to use it, the system crashes.

The UniDisk driver adds more disk-switched detection to what's in the drive and
as such will only work when attached to the internal port (GS/OS slot number
$0005).  As the generated drivers are created (which one would be for something
attached to a UDC, as it can't be in internal slot 5), the Device Dispatcher
tries to kick out generated drivers for Apple peripherals that it knows need
loaded drivers.  The UniDisk is one of these - without a loaded driver you
will eventually confuse the drive, miss disk switches and probably write
cached information (like directories) to the wrong disk.

What Central Point needs to do is write a generic 3.5" driver that claims
all the 3.5" drives attached to the UDC and handles them appropriately.

-- 
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Matt Deatherage, Apple Computer, Inc. | "The opinions represented here are
Developer Technical Support, Apple II |  not necessarily those of Apple
Group.  Personal mail only, please.   |  Computer, Inc.  Remember that."
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