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From: ced@apollo.uucp (Carl Davidson)
Newsgroups: comp.sys.apollo
Subject: Re: locking object info physical memory
Message-ID: <3c11243b.bf08@apollo.uucp>
Date: 15 May 88 14:35:00 GMT
References: <8805122134.AA04356@richter.mit.edu>
Organization: Apollo Computer, Chelmsford, Mass.
Lines: 44

From article <8805122134.AA04356@richter.mit.edu>, by krowitz@RICHTER.MIT.EDU (David Krowitz):
> I'm writing a device driver for a printer ...
> ... [text deleted]
> Here's my question: is there some way of locking an array, or some
> arbitrary piece of address space, into *physical* memory? ...
> ... [more text deleted]

Yes, but it's not pretty. You can use the "pbu[2]_$wire" calls (there are actually tow calls,
pbu_$wire and pbu2_$wire).

These calls are declared like this (in the Pascal insert files):

PROCEDURE pbu2_$wire (                      { wire an I/O buffer }
            IN  unit : pbu_$unit_t;         { unit number }
            IN  buffer : UNIV pbu_$buffer_t;{ buffer to be wired }
            IN  length : linteger;          { length of buffer (in bytes) }
            OUT status : status_$t          { returned status }
            ) ; EXTERN;

		(In pbu_$wire, the length parameter is 2 bytes instead of 4)

To be able to use these calls, your process must have acquired a pbu device (i.e., a device in the
peripheral bus).  If you don't, the error "unit in use" will be returned.  In cases like yours (it 
sounds like you are really writing a printer driver, not a device driver), you have to go out of 
your way to do this.

What you must do is write a dummy GPIO device driver consisting of a do-nothing initialization routine
nd a do-nothing cleanup routine.  Then specify an unused pbu unit number in the DDF (device descriptor
file) for your dummy device.  Finally, in your print driver, use "pbu_$acquire" to initialize the dummy
device driver prior to trying to wire any buffers with pbu2_$acquire.  Also be sure to call
pbu_$release prior to terminating the print driver.  See the Apollo manual "Writing Device Drivers with
GPI/O Calls", Order NO. 959, for details on the above steps.


If you are actually writing a GPIO device driver, then you will already have a GPIO unit number
allocated.  Then all you have to do is call the appropriate call. I recommend that you always use
"pbu2_$wire", for simplicity's sake (it lets you wire larger buffers).

Hope this helps!
-- 
--Carl Davidson                                 "Science is what you do
  Apollo Computer Inc.                           after  you  guess well."
  Chelmsford, MA 01824                 
  {decvax,mit-eddie,umix}!apollo!ced