On Wednesday 16 March 2005 10:25, Eric Shibata wrote: >Hi Gene, >Do you mean interrupts? >When I look at my /proc/interrupts I know I have other things there > with my scsi adapter from BusLogic. > >-------------------------------------------------------------------- >---------------------------------------------- CPU0 > 0: 70937522 XT-PIC timer > 1: 200 XT-PIC i8042 > 2: 0 XT-PIC cascade > 8: 1 XT-PIC rtc > 11: 368831 XT-PIC BusLogic BT-930, uhci_hcd, eth0 > 12: 4778 XT-PIC i8042 > 14: 90206 XT-PIC ide0 > 15: 212674 XT-PIC ide1 >NMI: 0 >ERR: 0 >----------------------------------------------------------- >Let's just say it was a cabling problem. When I insert the tape, it > makes sound like it's rewind the tape. Would it be able to do that? Yes of course it would. The drive is fairly smart, and the first thing its going to do when it senses that a tape has been inserted is to rewind it, then inspect the header to determine what kind of a tape it is, and if it has internal options to drive that legacy tape if its say, a dds3 tape being loaded into a dds4 drive. So it will make some noises all by itself while doing this. Now, I hate re-teaching how to re-invent a wheel here, the wheel thats called 'scsi cableing, care and feeding' or some such silly attempt at being a smart-ass on my part. I have done a nomogram like this before, on this list, but not recently. I am a broadcast engineer, where transmission line termination errors can easily cost us $50,000 or more in stuff burned up. But here goes anyway. Bear with me folks. lecture mode on 1. A scsi cable is a transmission line, and as such absolutely must be properly 'terminated' at both ends of the cable, and only at the ends. As little as 6" of unused cable hanging from one end or the other, past the connectors that are in actual use, is enough to setup some echo conditions in the signal transmission that will wreck any chance of data integrity being attempted to be sent over the cable. Therefore, the card must have its terms enabled unless there are cables on both the internal connector and the external connector. Said another way, if the card has an external connector, but it is not in use, then the cards terms must be turned on. This can be in older cards, done by plugging in the 3 termination resistor packs in the SIL sockets provided on the card, or in later cards, possibly by a software option accessable via the cards own bios extensions that you see flash up on screen for a few seconds during the machines post. 2. Likewise, the far end termination must be done at the physical end of the cable, not at some socket in the middle of the cable. No unused cable is allowed to be hanging off the last used connection. Drives also vary these days in how they handle the termination, with far more drives requireing the resistor packs to be installed than not, although there is motion toward the use of what we call active terminations in this field too. If the drive isn't terminated, its not going to work UNLESS its not the last drive on the cable, in which case its perfectly legal for it not to be terminated. Its the last device that must be terminated. 2a. These terminations are the only 'loads' on the cable. The drive itself, and the cable, are all designed in a wired OR configuration, where the terms provide the logic one pullup voltage, and any device on the bus can turn on a transistor and pull that data line to ground. When they are 'off', the devices present a very small loading on the cable so that many devices can share a cable. There is extensive collision avoidance built into the protocol, so that when more than one device does this, its detected and dealt with. Silently, transparently, and often with no more than a couple of milliseconds delay in completing the data exchange the device requested. 3. There are extant, many cards whose term voltage isolation diodes are common power type silicon diodes. Some, and I have no idea if the buslogic is among them, have used a schotkey diode for this, cutting this voltage loss by about 2/3rds. The reason for the diode is to prevent the case where the computer psu is turned off, but an external drive enclosure is not, and that drive enclosure is also supplying termination power to run these resistor packs to the 'TP' line in the cabling. In that event, the computer would then be powered from the drive exclosure if it weren't for this diode preventing it. Where the type of the diode becomes a factor is when one is dealing with a cable that despite so-called proper termination on both ends, is still allowing some ringing on the edges of the signal transitions. When the term supply is reduced from its designed value of 5 volts because of losses in this diode, then the logic one noise margin fades away from its designed value of having the logic one resting voltage, wholly established by these terminators, fall from the designed value of 600 millivolts above that voltage which is guaranteed to be a logic one (2.4 volts), to as little as 100 millivolts, at which point it doesn't take much ringing to get a dip down into the voltage range that is officially defined as 'indeterminant', and you have a detected logic error, not often correctly reported in the logs, just a coverall, sometimes meaningless, error that its not working. This has become a much smaller consideration where the so-called active terms are in use. But lets talk 'transmission lines' a bit, at the physical level of the cable you've had in your hands already. That cable, when a length of it is inspected with the measureing tools available, and considering that every alternate wire in the cable is a ground wire (unless the cable is being used in an hvd or lvd system), will have a characteristic impedance of about 122 ohms, give or take 10 or so due to tolerances in the ribbon cables manufacture. Now, if that cable has a 122 ohm load on both ends, a signal traveling down its length will be absorbed in these resistors, and nothing will come back like an echo, but then superimposed on the new voltage level this signal represents. The signals ring in other words, if looked at with a sufficiently broadband oscilloscope. A 100mhz scope is barely adequate. To achieve this termination way back in time 35 years ago, and still in use today, it was common to use these resistor packs, which consist of a 220 ohm resistor with one end tied to the term power supply of nominaly 5 volts, the other end connected to the data line being terminated, and a 330 ohm resistor is also tied to this data line with the far end of it being grounded, those values being used because thats what the resistor makers had to offer at Orville Redenbacher's "popcorn" prices. This establishes a termination resistance value by the normal rules for paralleled resistances of around 132 ohms. Moderately close, and given correct noise margins, a generally workable scheme. But, what happens when that 5 volts is reduced by the nominally .6 to .75 volt drop of the silicon diode in series with that voltage? Well, the expected 3 volts for a logic one can drop, often to the point that this resistive scheme so carefully worked out 35 years ago, actually presents only a 2.58 volts logic one level, and only 180 millivolts of the 600 millivolt noise margin is left. Then couple that with the fact that the psu itself may be sagging and the 5 volt line is only 4.85 volts at the connectors where the drive is drawing power from. Then you have a logic one voltage of only 2.4 volts, the noise margin has all been used up and no amount of virgins sacrificed is going to make it work. Ever. When the terminations are made 'active', this is marketing speak for having a seperate 3 volt regulator set up on the card, and possibly the drive, with enough 120 ohm resistors coming off of it to feed every data line in the cable by its designed 3 volts, and it comes closer to actually matching the impedance of the typical ribbon cable to boot. And it has the added advantage of only drawing power when the bus is active, unlike the resistor packs, which drew 320 milliamps from a sometimes scarce power resource when resting, and proportionatly more when active, in portable applications this became a major source of power loss to be gotten rid of. In short, active terminations beat passive any day of the week when the variations of the real world are plugged into the formula. In your case, I suspect the drive is not terminated at all, and the cable is, electrically speaking, ringing like a bell. Or that you have the drive connected at a cable plug that is not the last one on the cable. The quality of the terminations can only be assessed with high bandwidth oscilloscopes, but a very very good idea can often be had just by measuring the resting voltage of a data line with everything powered up and that can be done with a $20 dvm from radio shack. If its above 2.9 volts on the cable with first one end unplugged, then plug that one back in and unplug the other and recheck, then the chances are you are pretty good and have other hardware problems. No, or very little voltage when one end of the cable is unplugged means the device the cable is still plugged into isn't terminated and this must be fixed. If its only 2.65 to 2.75, its going to be a problem child occasionally. Below 2.5 and its likely its not going to work until the proper voltage is re-established. I haven't dealt with the logic zero noise margin considerations because its a zero if the line is pulled down to less than .6 volts, and I've not seen the scsi bus driver yet that couldn't pull the line to well below 25 millivolts, hence its generally not a problem. If it can't, the driver chip is toasted, go get someone who knows which end of a soldering iron gets hot. I do, but I've yet to have to replace one because of that. Now, I hope I've helped to clarify this thing called a 'scsi bus'. lecture mode off > This is my first time setting up a tape drive, it didn't sound like > it should be this difficult. >Thanks, >ERS > >On Tuesday 15 March 2005 12:14, Eric Shibata wrote: > >HELP! > >I can't even get the status. No matter what I do I get the > > following error. > > > >/dev/tape: Input/output error > >/dev/st0: Input/output error > > > >Tape drive: HP SureStore T4i > > > >ERS > >That sounds a bit like cabling and or termination problems. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) 99.34% setiathome rank, not too shabby for a WV hillbilly Yahoo.com and AOL/TW attorneys please note, additions to the above message by Gene Heskett are: Copyright 2005 by Maurice Eugene Heskett, all rights reserved.
