Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-lcc!ames!think!ephraim
From: ephraim@think.COM (Ephraim Vishniac)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Apple HD SC 80 does not support Asynch i/o.
Keywords: Hall of Shame entry?
Message-ID: <35212@think.UUCP>
Date: 6 Jan 89 14:35:15 GMT
References: <11605@dartvax.Dartmouth.EDU> <271@berlin.acss.umn.edu> <872@lts.UUCP> <315@taniwha.UUCP>
Sender: news@think.UUCP
Reply-To: ephraim@think.com (Ephraim Vishniac)
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 23

In article <315@taniwha.UUCP> paul@taniwha.UUCP (Paul Campbell) writes:

>By the way the IWM doesn't generate interrupts either, I guess it
>probably uses VBLs while the hardware is seeking.

You're half right, and I was half right.  (I had earlier asserted that
the floppy driver was interrupt driven, and that the IWM did generate
interrupts.)  Looking at IM II-197, I see that the Disk Driver (i.e.,
.Sony since this is IM II we're reading) is blessed with exclusive use
of VIA timer 2.  No interrupt slot is shown for the IWM.

So, things look like this:

	. The floppy driver uses interrupts, but
	. There are no IWM interrupts, but
	. There is a VIA timer reserved for the floppy driver, so
	. The floppy driver doesn't use a VBL task.


Ephraim Vishniac					  ephraim@think.com
Thinking Machines Corporation / 245 First Street / Cambridge, MA 02142-1214

	"He shook his head to clear a momentary system error."