[mod.computers.sequent] Balance 8000 Answers

info-sequent-request@im4u.UUCP (12/16/85)

From: sequent!parsons@ut-sally.UUCP (Ron V. Parsons)

The following are answers to some of the questions that have been posted
to info.sequent:


DO THE TAPE DRIVES OVERHEAT?

	The Cipher tape drive used on a Balance 8000 at one site did 
overheat.  Cipher investigated the problem, replaced the drive,  and 
issued an Engineering Change Order for the drive's microcode.  The change 
keeps the unit's fans on longer.  This solves the problem.

HOW DO I GET TO THE MULTIBUS ADDRESS SPACE?

	If you want to write to a Multibus address, you have two techniques
you can use.  The first is to write a device driver.  The Multibus(es)
appear in the machine's physical address space just like memory.    There
is a good write-up on it in the 'Balance 8000 Technical Summary,' which
is a part of the manual set.  It happens to be used as a sales tool, so
being nice to a Sequent salesman is one route to acquiring a copy.  The
manual 'Guide to Writing Device Drivers' that comes with the Balance 8000
gives the details of the data structures involved.

	The second technique is to map to the Multibus address space from
inside a user-mode program.  This is done with the mmap system service.
It is normally used for creating shared memory, however it also supports
physical address mapping.  It creates virtual address space for you and 
puts it anywhere in the physical address space you might like.  You can
then address the Multibus address space without going through a driver.
Be REAL CAREFUL to use only byte and word instructions when referencing
the Multibus.  If you try to move 32 bits in one instruction, the machine
will get real excited about it.

HOW DO I AVOID CSR ASSIGNMENT CONFLICTS?

	If you do the 'dmesg' command on a Balance 8000, it will show you
the messages generated by DYNIX during the last bootstrap.  Included is
a listing of every device out on the Multibus and the address of it's
csr.  Using this, it's easy to avoid address conflicts.  The big disk
controllers start at 100,  the asynchronous multiplexers start at 200,
the tape controllers start at 300.  So, if you start at, say, 800, you
will be OK.