From:	kunst AT prl DOT philips DOT nl (Pieter Kunst)
Subject:	Re: Accessing physical addresses again...
To:	mll AT krypton DOT jsc DOT nasa DOT gov (Mark Littlefield)
Date:	Thu, 4 Feb 93 17:18:35 MET
Cc:	djgpp AT sun DOT soe DOT clarkson DOT edu (DJGPP users list)
Mailer:	Elm [revision: 70.30]

Mark L. Littlefield writes:

> Sorry to bring this up again but we've been having mail problems here 
> and apparently I was accidentally dropped from the list for a time so 
> I didn't see any responses from my last query.
> 
> What I need to do is access certain memory locations in the 0xE0000000 
> memory range (>256 > meg).  These locations are mapped to the VME bus 
> that our 486 is attached to. I've look at the docs and the sources and 
> I don't see an obvious way of addressing physical memory in protected 
> mode (all of the memory gets mapped one way or another).
> 
> If there was any discussion on this topic after my last query I would 
> appreciate it if some kind soul would forward the responses to me.
> 


Mark L. Littlefield writes:
> 
> We are planning to run a set of djgpp-compiled programs on a 486
> based, VME bus, PC.  To work with the bus, we need to access
> physical memory above 256 meg (this memory reads and writes directly
> to the bus).  My question is, how do we work with this memory using
> djgpp/go32? 
> 

I've been doing the same thing for a while...
You have to add some code to the GO32 program (DOS extender).
(If anyone shows you how to do it without patching GO32
I would like to know too !)

I had the additonal problem that the access to my VME memory
is paged, i.e. I can't access all memory at the same time.
I therefore wrote some sort of (automatic) page fault handler
specific for the VME memory (but comparable to the video page
fault handler of GO32).

The netto result is that I can access 16 Mb of VME memory
'directly' at location 0xA0000000 using GO32 programs.
(Works fine for me, only requires to redo the patch for every new
release of GO32...)

If some other user has given you a better clue, I would like
to know too. If you are nevertheless interested in the patches
let me know so I can spend a bit more time sending them to you.

--

Pieter Kunst (kunst AT prl DOT philips DOT nl)

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