Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utcs!wagner From: wagner@utcs.UUCP Newsgroups: comp.sys.amiga Subject: Re: Amiga Multi-tasking Overhead Message-ID: <1986Dec21.165050.4430@utcs.uucp> Date: Sun, 21-Dec-86 16:50:50 EST Article-I.D.: utcs.1986Dec21.165050.4430 Posted: Sun Dec 21 16:50:50 1986 Date-Received: Sun, 21-Dec-86 17:35:20 EST References: <1986Dec2.102542.4658@utcs.uucp> <1085@cbmvax.cbmvax.cbm.UUCP> <1986Dec11.185731.13459@utcs.uucp> <926@midas.UUCP> Reply-To: wagner@utcs.UUCP (Michael Wagner) Organization: University of Toronto Computing Services, general purpose UNIX Lines: 29 Checksum: 41098 In article <926@midas.UUCP> jacc@midas.TEK.COM (Jac Colby) writes: >When I was trying to figure out how to add my own external disks, >I noticed that the select lines went active once every second if a >disk was not present in a drive. When a disk is placed in a >drive, its presence is always detected within one second, and the >validator is run. However, the select lines *continue* to be >pulsed, and at an even higher rate. I presume that this is done >to check for disk removal. The disk-removed signal is active low, >so detection of disk removal or insertion must be done by polling. >An obvious question, though, is why doesn't the trackdisk.device >just check for disk-removed prior to each disk access? A very interesting observation, that sent me scurrying for my manuals. In the RKM (part2), the discussion of the trackdisk.device includes the command TD_REMOVE. This nominates your routine to get control when a disk is removed. I guess you could use this support to put up a requestor and say PUT THAT BACK! or something. Sounds marginally useful. The trackdisk driver promises to check and tell you, in any case, when you go to do I/O. So, you ask, how does it do this? Well, the hardware manual claims there is a signal. However, it doesn't interrupt at the point of removal. Rather, 'the drives that support this signal latch it until the next time the heads are stepped'. Is it perhaps stepping the heads on a regular basis to see if the disk got removed? If so, could it be induced to be a little less eager? Michael