Newsgroups: comp.sys.mac.hardware Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!oxtrap!oxtrap!time From: time@oxtrap.oxtrap.UUCP (Tim Endres) Subject: Re: Sharing the SCSI bus? In-Reply-To: mclow@telesoft.com's message of 20 Nov 89 04:49:02 GMT Message-ID: Sender: time@oxtrap.aa.ox.com (Tim Endres) Reply-To: time@oxtrap.UUCP Organization: Oxtrap - Ann Arbor, MI References: <1240@key.COM> <602@telesoft.com> Date: 27 Nov 89 14:04:27 In article <602@telesoft.com> mclow@telesoft.com (Marshall Clow @telesoft) writes: From: mclow@telesoft.com (Marshall Clow @telesoft) In article <1240@key.COM>, perry@key.COM (Perry The Cynic) writes: > ... Intro > > ... a discussion about SCSI ... > > Can the Mac's SCSI chip and manager (esp. > the manager!) cope with a second talker on the bus? I.e., can the PC card > talk to the CD-ROM player while the Mac talks to a harddrive? Am I expecting > much too much of the poor weak-brained SCSI manager? It won't work. As you surmised, the Mac's SCSI manager wants to be the only "initiator" on the bus. If you want to get technical, _SCSISelect ( or whatever the trap is called ) will fail if the Mac cannot get control of the bus. ( i.e, if two other devices are communicating ). Sorry bout that. It would be a neat hack. Marshall Clow mclow@telesoft.com Sorry, Marshall, but it will work. In fact it is done all the time! Talk to anyone with an Ensoniq EPS. Yes, _SCSISelect() can fail, but most programs deal with this. Further, other initiators on the bus does not necessarily mean that SCSISelect() will fail. The probability of a timeout on select increases, but this does not translate into failure. In fact, the opposite tends to be true, the Select almost never fails. Multiple initiators is an *important* aspect of SCSI. I wish more people would excersize it to be sure Apple keeps it functional. Disclaimer: Anything can be done. It is a matter of cost.