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From: tj@kona.cs.ucla.edu (Tom Johnson)
Newsgroups: comp.sys.mac.hardware
Subject: Re: One HD, two Macs
Message-ID: <1991Jan12.012032.23037@cs.ucla.edu>
Date: 12 Jan 91 01:20:32 GMT
References: <130402@jake.encore.com> <130424@jake.encore.com> <130426@jake.encore.com>
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In article <130426@jake.encore.com> mjw@encore.com (Mike Willegal) writes:
>
>On the other hand it probably would be an easy hack to change the ID in
>the driver, if you had a little time.

Actually the SCSI ID of the macintosh is stored in the Parameter Ram.
If you feel particularly adventurous and want to look for yourself, try
the following Think C 4.0 code:

----cut here----
 pascal void ReadXPram()  = {0x201F,0x205F,0xA051};
 pascal void WriteXPram()  = {0x201F,0x205F,0xA052};


main()
{
	char	DelayByte,SCSIid,delayedDrive;
	ReadXPram(&DelayByte, 0x01,1);
	ReadXPram(&SCSIid,0x02,1);
	ReadXPram(&delayedDrive,0x03,1);
}

----and here----
ReadXPram and WriteXPram each take a ptr to the variable, the location
of the value to be read and the number of bytes to read.  I was playing
around with this when we got a couple of 330Mg Wren VI drives which
don't spin up very quickly--we had internal Quantom 170Mg drives in the
machines (the Wrens were external, of course) and we found we couldn't
startup from the Wren from a cold start if both machines had System Folders.
We set the Wren as the startup device, but the mac would time out before
the Wren was ready to go, so it would only boot off of the Quantom. I changed
the DelayByte to 0xC8 and the delayedDrive to the SCSI ID of the Wren and
it worked fine--the mac waited long enough for the Wren to get running.
My source told me of the Mac SCSIid location just as a curiosity.

Have fun, but be aware that I don't take any responsibility for what
you do to your poor macs and drives when you change the scsi ids!!!

Tom


-- 
Tom Johnson      UCLA Computer Science Department 
			3413 Boelter Hall, Los Angeles CA 90024 (213)825-2145
			Internet:  tj@cs.ucla.edu