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From: berger@datacube.UUCP
Newsgroups: comp.unix.wizards
Subject: Very Large Framestores on Sun: addr
Message-ID: <106600006@datacube>
Date: Thu, 5-Mar-87 18:16:00 EST
Article-I.D.: datacube.106600006
Posted: Thu Mar  5 18:16:00 1987
Date-Received: Sun, 8-Mar-87 05:41:08 EST
Lines: 38
Nf-ID: #N:datacube:106600006:000:1648
Nf-From: datacube.UUCP!berger    Mar  5 18:16:00 1987


Sun  tech  support  can't  help  me,  maybe  someone on  the net can!

I want to map a very large chunk of physical memory (32  Meg of video
frame-store) into my user process's virtual address space.  

We have a Sun 3/75 connected to  an external  VME chassis  with a bus
repeater capable of repeating a full  A32 /  D32 bus  to the external
VME chassis.  

In this chassis we have a very large frame store that takes up 32 Meg
of physical memory.  

We have been told that the only way to map the physical memory of the
frame-store  into  a user  program is  to first  do a  valloc which I
presume reserves pages in the MMU for a chunk of memory,  and then an
mmap which maps the physical memory into the  reserved virtual memory
chunk.  This is how frame-store's are usually mapped in on the sun.  

The  problem  is  that  the valloc  actually allocates  the amount of
memory you are requesting.  If you don't have enough swap space free,
the valloc fails.  Thus not allowing you to get  a chance  to map the
physical to virtual address.  

They  say  that this  will be  changed in  version 4.0  of Sun OS....

There must be  a more  sane way  to tell  the operating  system / MMU
hardware to do an explicit mapping  today!   What good  is having A32
VME  bus addressing  if you  can't talk  to large  chunks of physical
memory?  I consider this a major failing if its  true that  a Sun can
not do this.  

				Bob Berger 

Datacube Inc. Systems / Software Group	4 Dearborn Rd. Peabody, Ma 01960
VOICE:	617-535-6644;	FAX: (617) 535-5643;  TWX: (710) 347-0125
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