Path: utzoo!attcan!uunet!lll-winken!ames!mailrus!purdue!decwrl!labrea!polya!kaufman
From: kaufman@polya.Stanford.EDU (Marc T. Kaufman)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Apple HD SC 80 does not support Asynch i/o.
Message-ID: <6006@polya.Stanford.EDU>
Date: 10 Jan 89 17:06:29 GMT
References: <11605@dartvax.Dartmouth.EDU> <271@berlin.acss.umn.edu> <27318@ucbvax.BERKELEY.EDU> <13271@cup.portal.com> <5958@polya.Stanford.EDU> <13369@cup.portal.com>
Reply-To: kaufman@polya.Stanford.EDU (Marc T. Kaufman)
Organization: Stanford University
Lines: 18

In article <13369@cup.portal.com> ts@cup.portal.com (Tim W Smith) writes:
>Apple means not to poll from interrupt level ( such as vertical retrace
>tasks ).  These can interrupt while another SCSI operation is in
>progress.

>The hard part is that there are people out there that assume that
>they are the only ones going against Apple recommendations.  If all
>the people that had to poll at interrupt time got together, we could
>agree on some convention to avoid wiping each other out.

I first thought that it would be sufficient to check for BUSY status before
doing a SCSIget, but I see that an interrupt could occur between the check and
the Get.  I haven't tried to trace SCSIget, but I think that an indivisible
check-and-get (i.e. with interrupts off), that returned busy status if the
bus was already in use, would work.  Is this worth a system patch? or does
SCSIget already check for busy?

Marc Kaufman (kaufman@polya.stanford.edu)