Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hpcvca!charles From: charles@hpcvca.CV.HP.COM (Charles Brown) Newsgroups: comp.sys.amiga.tech Subject: Re: Apple SCSI not compatible with standard SCSI? Message-ID: <1410035@hpcvca.CV.HP.COM> Date: 29 Nov 89 02:30:03 GMT References: Organization: Hewlett-Packard Co., Corvallis, Oregon Lines: 75 >>The particular spec involved the time from reset to ready. The >>Commodore will not autoboot if that time is greater than (as I recall) >>four seconds. The Miniscribe appears (from my informal measurements) >>to take about 5 seconds if warm booting with the head on track 2, >>about 8 seconds if warm booting with the head near the middle track, >>and about 14 seconds from power up. > The problem is not the time from RESET to ready, but the time from RESET > to response to commands. Seagate drives have this same problem. When the > drive is spinning up from cold start, it does not respond to selection at > all. This looks to the driver software as if no drive is hooked up. The > solution is to try for selection, if it fails wait a second and try again > up to a timeout limit. That is fine, except that the COMPETITOR's computers will successfully boot from these same disk drives. The customer does not say "what a pity my computer works with this drive when the drive is out of spec". The customer (me) says "I am not happy that the Amiga fails to boot with this drive. The other computer can, why not the Amiga?" > However, SCSI drivers have to check 7 distinct > SCSI bus addresses to see if drives are hooked up (there is a way under > the new RDB scheme to shortcut this check, but that`s not important here). > If the driver were to assume that all drives took at least 5 seconds to > spin up, that would be 7*5 = 35 seconds of dead time on a cold boot. Not true. The Amiga only attempts to autoboot from the first SCSI. So if the delay is extended to 10 seconds, the max wait would be 10 seconds. Notice that a customer would rarely see this delay. The algorithm looks something like: if there is a floppy boot from it no delay else if there is a ST506 boot from it short delay? else loop once a second did the SCSI respond? yes: boot from it delay of 1 to 10 seconds depending on how fast the drive responds no: prompt for a floppy <-- max delay slightly over 10 sec > Since > the majority of drives respond correctly, it does not make sense to > compromise systems with good drives for the few with bad ones (bad meaning > badly behaved). Compromised! The only delay this affects is the time to display the hand, and that delay only occurs if the following is true there is not a floppy in the drive AND there is a 2090A card AND there is not a bootable ST506 drive AND there is not a bootable SCSI drive Realistically, how often is that going to happen? That low probability is what you are balancing against the cost of having a number of drives which will not boot with the current firmware. It looks to me like about 30% of hard drives will not boot because of this spec. The 2090 users's guide (with the addendum) lists 8 that do and 4 that don't autoboot. If I include my data point (Miniscribe 3180S) that works out to 5/13=38% of known SCSI drives which will not autoboot. > This problem has been (sort of) addressed on the A590 and > A2091 by having a "Seagate" jumper on the board. If this jumper is > installed, much longer timeouts are allowed when cold booting the system. > steveb@cbmvax.UUCP (Steve Beats) I bought the A2090A because it was supposed to autoboot. Now it appears I need to buy the A2091 to autoboot. I hope you understand my frustration. -- Charles Brown charles@cv.hp.com or charles%hpcvca@hplabs.hp.com or hplabs!hpcvca!charles or "Hey you!" Not representing my employer.