Physical memory access with SystemV/AT

[wtr at moss.ATT.COM]

In article <1019 at sdcc12.ucsd.EDU> mp1 at sdcc12.ucsd.EDU (Leroy Dorman) writes:
>In article <185 at focsys.UUCP>, larry at focsys.UUCP (Larry Williamson) writes:
>> I would like to do something like:
>> 	shmcreate 0x800000 800000 1048560
>> to create a 1Meg shared memory segment at the 8meg address location.

>Unless Microport put in a peek/poke-style function in to V/AT,
>(the Rel 1.0 from At&t didn't have one)
>there's no way to access physical memory from u-space.

>You're right, it sure would be nice to assign a physical memory
>location to a segment selector so you can get at it in
>large-model user space programs.

>Eric Dorman

eric -

"what we have here is a failure to communicate" :-)

microport V/AT allows root (via a shell script executed at bootup)
to reserve specific memory locations as a shared memory resource.
this allows you (the user) to access such wonderous areas as the 
display memory DIRECTLY!  i currently am working with a set of 
graphics primatives that write directly to the screen, and you dont
have to be root to do it, nor are there any nasty drivers to play
with.


larry-

the only thing that i can suggest, since the [not really] large
model supports only 64k arrays is to make 16 reserved sections
of 64k memory to use for your 1 megabyte display buffer.  
probably use an array of 16 pointers to move this monster 
around.  

i don't have the manual here right now, so this is a standard
disclaimer to quench any "you don't know what the &^*% you're..."
postings which may follow.  i believe that the above suggestion
will work, and i can think of any better method.

good luck!

=====================================================================
Bill Rankin
Bell Labs, Whippany NJ
(201) 386-4154 (cornet 232)

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