SCSI ID Prioirty (and SCSI cable question)?

Tempest 2084 · 12 June 2016, 03:06

Dumb question, but is it the higher the number the higher the priority or is it the opposite? I have a GVP HD8+ SCSI card in my A2000 and I'm trying to figure out what to ID to set the hard drive and the CD Drive to. Right now I have the HD set to 2 and the CD to 0 (the board itself is set to 7 per the manual's instruction).

The reason I ask is that I'm getting odd random crashes when I have the CD and the hard drive hooked up together and I'm trying to figure out if there's a conflict somewhere or if it's the cable itself. At the moment I'm leaning towards the cable being the culprit since I got the crashes even when I disconnect the CD drive BUT they went away when I used a short two connector cable to hook up just the hard drive (the other cable is a long 4 connector cable). I'm wondering if I'm running into odd 'SCSI voodoo' issues (sorry, that's an old Mac term, but it seems to apply here).

idrougge · 12 June 2016, 04:24

There is no priority on SCSI IDs on the Amiga. Check your termination.

Tempest 2084 · 12 June 2016, 04:33

Ok that's good to know. I have a cable that has a terminator and the cd rom drive has the ability to terminate. Does it matter which I use? Does the number of connectors on the cable matter?

Daedalus · 12 June 2016, 04:58

Okay, some SCSI basics. No, the number of connectors doesn't matter. No it doesn't matter what you use to terminate the cable. What's important is that there is exactly one terminator at each physical end of the cable. No more, no less. No ifs, no buts. That's the most basic rule. After that, every device needs to have a unique ID including the host (which is frequently ID 7). Once you've got that far, devices will be loaded in order but nothing will get a chance before all devices have been read, so priority doesn't mean a great deal in SCSI land.

There's no magic about SCSI, you just have to follow the rules without any "ah, this might be ok" or "surely this doesn't matter" type ideas. Follow the rules, only the rules and no rumours, and it will work 100%.

Tempest 2084 · 12 June 2016, 05:22

Then I wonder what was causing my crashes then? It has to be something with the termination since as you said, the cable itself doesn't matter. The odd thing was that when it crashed, I didn't get a guru error, I just got a blank screen the same color as the background (like all the graphics went away). I've never seen that before.

idrougge · 12 June 2016, 05:41

TERMINATOR ---- CARD ---- DISK ---- DISK ---- TERMINATOR

(The terminator on your card is usually two or three things looking like this: mmmm)

Daedalus · 12 June 2016, 17:19

It could be an actual fault with the cable. Try hooking up each drive by itself on the 4-connection cable and see if they work by themselves. It could also be an incompatibility of one of the drives' settings for reselection, synchronous etc. To start with, make sure everything's set to asynchronous. It's slower but more compatible, and is usually the default of any controller.

Tempest 2084 · 12 June 2016, 22:16

The new cable seems to work. Must have been a wonky cable or something.

12 June 2016, 03:06	#1
Tempest 2084 Prototype Historian Join Date: Apr 2009 Location: SE MI / USA Posts: 420	SCSI ID Prioirty (and SCSI cable question)? Dumb question, but is it the higher the number the higher the priority or is it the opposite? I have a GVP HD8+ SCSI card in my A2000 and I'm trying to figure out what to ID to set the hard drive and the CD Drive to. Right now I have the HD set to 2 and the CD to 0 (the board itself is set to 7 per the manual's instruction). The reason I ask is that I'm getting odd random crashes when I have the CD and the hard drive hooked up together and I'm trying to figure out if there's a conflict somewhere or if it's the cable itself. At the moment I'm leaning towards the cable being the culprit since I got the crashes even when I disconnect the CD drive BUT they went away when I used a short two connector cable to hook up just the hard drive (the other cable is a long 4 connector cable). I'm wondering if I'm running into odd 'SCSI voodoo' issues (sorry, that's an old Mac term, but it seems to apply here).

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12 June 2016, 04:24	#2
idrougge Registered User Join Date: Sep 2007 Location: Stockholm Posts: 4,362	There is no priority on SCSI IDs on the Amiga. Check your termination.

12 June 2016, 04:33	#3
Tempest 2084 Prototype Historian Join Date: Apr 2009 Location: SE MI / USA Posts: 420	Ok that's good to know. I have a cable that has a terminator and the cd rom drive has the ability to terminate. Does it matter which I use? Does the number of connectors on the cable matter?

12 June 2016, 04:58	#4
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,401	Okay, some SCSI basics. No, the number of connectors doesn't matter. No it doesn't matter what you use to terminate the cable. What's important is that there is exactly one terminator at each physical end of the cable. No more, no less. No ifs, no buts. That's the most basic rule. After that, every device needs to have a unique ID including the host (which is frequently ID 7). Once you've got that far, devices will be loaded in order but nothing will get a chance before all devices have been read, so priority doesn't mean a great deal in SCSI land. There's no magic about SCSI, you just have to follow the rules without any "ah, this might be ok" or "surely this doesn't matter" type ideas. Follow the rules, only the rules and no rumours, and it will work 100%.

12 June 2016, 05:22	#5
Tempest 2084 Prototype Historian Join Date: Apr 2009 Location: SE MI / USA Posts: 420	Then I wonder what was causing my crashes then? It has to be something with the termination since as you said, the cable itself doesn't matter. The odd thing was that when it crashed, I didn't get a guru error, I just got a blank screen the same color as the background (like all the graphics went away). I've never seen that before.

12 June 2016, 05:41	#6
idrougge Registered User Join Date: Sep 2007 Location: Stockholm Posts: 4,362	TERMINATOR ---- CARD ---- DISK ---- DISK ---- TERMINATOR (The terminator on your card is usually two or three things looking like this: mmmm)

12 June 2016, 17:19	#7
Daedalus Registered User Join Date: Jun 2009 Location: Dublin, then Glasgow Posts: 6,401	It could be an actual fault with the cable. Try hooking up each drive by itself on the 4-connection cable and see if they work by themselves. It could also be an incompatibility of one of the drives' settings for reselection, synchronous etc. To start with, make sure everything's set to asynchronous. It's slower but more compatible, and is usually the default of any controller.

12 June 2016, 22:16	#8
Tempest 2084 Prototype Historian Join Date: Apr 2009 Location: SE MI / USA Posts: 420	The new cable seems to work. Must have been a wonky cable or something.

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