Very Computer

by **Simone Navar** » Thu, 27 Jun 2002 15:41:41

I had to allocate a physical memory block to use it as a DMA buffer.
Under plain DOS, no problem ! To do it I use XMS services to allocate
and lock memory but if I try to do it in a Windows Dos Box, the
operating system halts my software when it calls the XMS lock service.
Why Windows don't allow me to do this operation ?

I've heard that VDS services can solve the problem but I don't
completely understand how use it and how it can solve my problem !

Any help will be apreciated....

Simone Navari.

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by **Vinzent Hoefle** » Fri, 28 Jun 2002 04:02:52

>To do it I use XMS services to allocate
>and lock memory but if I try to do it in a Windows Dos Box, the
>operating system halts my software when it calls the XMS lock service.
>Why Windows don't allow me to do this operation ?

Because Windows handles the memory in a virtual (paging) way, it can't
give you a physical address for such a block (it simply does not
exist), what the plain XMS-service normally does. This would mean, it
could not throw out the locked block to the paging file if physical
RAM is needed in another task, the block had to be a complete
contiguous section (not good for paging) and in such a way it would be
easily possible to knock down Windows by using all available memory
from within a DOS-session without any dirty tricks...

Vinzent.

Very Computer

DMA use in a Windows Dos Box (pls help)

DMA use in a Windows Dos Box (pls help)

DMA use in a Windows Dos Box (pls help)