Adding 3rd party peripherals to a DecStation 5xxx.

[Michael Paddon]

>From article <897 at sibyl.eleceng.ua.OZ>, by ian at sibyl.eleceng.ua.OZ (Ian Dall):
> We are getting a DecStation 5xxx (not sure which one here) but it
> hasn't arrived yet so I can't "look and see" what comes as standard in
> Ultrix. I want to put a QIC-24 compatable SCSI interface tape drive on
> the system. In the future we might want to put other 3rd party SCSI
> devices on it.
> 
> What I want to know, is whether Ultrix device drivers allow this.  On
> at least one other SCSI based system I know of, the minor device no.
> is mapped into SCSI unit numbers so that adding a new tape is just a
> matter of mknod'ing the correct entry in /dev.  We will have one (non
> QIC-24) DEC tape drive so a tape driver will be there.
> 
> How difficult is it to add new device drivers? Is the interface
> between the SCSI interface and the tape and disk drivers well defined?
> Is source for the device drivers supplied?

There is a SCSI tape driver included in Ultrix 4.X. To allow the use of
a tape drive with SCSI address 'X', you must configure a kernel with the
line looking like this in the config file:
	tape            tzX        at asc0      drive X
(at least that's true for my DS5000).

Then all you have to do is mknod (or better yet use MAKEDEV, which
knows which major/minor numbers to use) the correct entry in /dev.

However, there is one slight problem...
Not all SCSI tape drives are created equal. You may have to add an entry
to the tape_opt_tab table in /usr/sys/io/scsi/mips/scsireg.h to describe
the capabilities and SCSI parameters of your particular drive. There is
a fairly detailed comment in that file explaining exactly how to do this.

In general, new drivers are as easy to add to Ultrix 4.X as they have
ever been (ie. straightforward so long as you know what you are doing).
Of course, you don't need to add a new driver for SCSI tape or disk -- they
are already there. Finally, source to these drivers is *not* supplied, but
you can do substantial tweaking via include files.

					Michael

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