8mm and 1/4" SCSI addressing problem

8mm and 1/4" SCSI addressing problem

Post by Victor Gru » Tue, 23 Oct 1990 10:43:09

Just a small contribution to the net...

We've noticed that customers getting both the 8mm and 1/4" tape drive
options on their systems are getting both devices configured with
SCSI address 2.  Tapes will read a bit from these drives with
conflicting addresses, then give you the old "read error, assuming
zeros" message.  This should've been the first thing I checked, but it
wasn't and I wasted a good bit of time before I noticed it.

This is easily fixed by changing the address of one of the drives to a
free SCSI address by rotating the address knob on the back of the

Victor Grund


IBM Cleveland &                 | uunet!cwjcc!pyrite!grund
Case Western Reserve University | RISC System/6000 ---> Catch the Wave...
Cleveland, Ohio                 | Home of the Cleveland Orchestra!


1. "Kernel logical address" vs "Physical address"

 I have a fairly basic question about "Kernel logical address" and "Physical

In the book about Linux Device Drivers from Alessandro Rubini I read:

"Logical addresses make up the normal address-space of the kernel. . On most
architectures, logical and their associated physical addresses differ only
by a constant offset." __pa() is used to go from logical address to Physical
address; __va() the other way round.

I have been working on a PPC platform, running Linux 2.2. This platform has
a register where you can enable different options and where you can control
several LED's. The vendor mentions that this register is mapped in memory at

When I write (in a driver)

char *p=0xFA40000;

*p = ..; (I know I should use writeb to be more portable.)

it seems to work; the leds can be manipulated. But as FA400000 is a physical
address, I thought that it had to be *p=__va(0xFA40000);

Who can help me out? Where do I find a nice document about this?



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