🚀 go-pugleaf

In article <1992Sep29.070357.23292@CS.ORST.EDU>, @prism.cs.orst.edu writes:
> I need to allocate two 64k buffers in ram from a 16bit device driver. Each of
> the buffers must be completely contained in a segment. They cannot cross a
> segment boundary. Does anyone know of a way to do this?
> 
> Thanks
> 
> Keith

Well, It sounds like you need a DMA buffer. You can use DevHelp VMAlloc
to allocate a large block of virtual memory( Specify non-swappable ).
Allocate at least 192K( you will waste a total of 64K if you want to allign
it on a 64K boundary, there will be some wasted above and below the range that
you want). The address that you get back will be Linear, so use DevHelp
LinToPagelist to get the physical address. take the Physical address you
recieve and adjust it to align on a 64K boundary. Then do a PhysToVirt of
the adjusted physical address to obtain a 16:16 addressable address of each 
block

The physical memory you want will look like this:

 ___________________________________________________ 
| Low           |            |           |  High    |
| Wasted 	| Block #1   | Block #2  | Wasted   |
| Area          |  =64Kb     |  =64Kb    | Area     |
| < 64Kb        |            |           |  < 64Kb  |
-----------------------------------------------------
                |            |           |
               64K          64K         64K
	    Boundary    Boundary     Boundary


Low Wasted Area + Block#1 + Block#2 + High Wasted Area = 192Kb

(size < 64K )   + 64K 	  + 64K	    + ( size < 64K ) = 192Kb

	
I hope that this help you. You may want to read up on VMAlloc, LintoPageList,
and PhysToLin in the IBM Physical Device Driver reference manual.

Michael Kupka
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(Happy Father of an OS/2 QIC-40/80 Driver)
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