Message-ID: <34879CFA.1D51@mailexcite.com>
Date: Fri, 05 Dec 1997 01:19:39 -0500
From: Doug Gale <dgale AT mailexcite DOT com>
Reply-To: dgale AT mailexcite DOT com
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Newsgroups: comp.os.msdos.djgpp
Subject: Un-map physical memory?
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To: djgpp AT delorie DOT com
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I am working on a function that will remap DOS memory into my heap.

I know that this won't work under Win95 (I think), but I am putting it
into my library and I need some suggestions.

First question, am I doing it right? Here's the source:

int	GL_RemapDOSMemory(void **pmode_ptr, void **map_block, unsigned
phys_addr,
		unsigned size)
{
	unsigned alloc_size = size * 2 + 4096;
	void *mapping_block;

	// Allocate memory region to map the dma buffer into
	if (!(*map_block = mapping_block = malloc(alloc_size)))
		return 0;

	// Page align
	if ((unsigned)mapping_block & 0xfffff000)
		*pmode_ptr = (unsigned char *)
				(((unsigned)mapping_block & 0xfffff000) + 0x1000);
	else
		*pmode_ptr = mapping_block;

	// Map physical memory into memory block
	if (__djgpp_map_physical_memory(*pmode_ptr, size, phys_addr) == -1)
		return 0;

	return 1;
}

(I know the comments mention DMA, but don't pay attention to this, it
was a copy/modify of my GL_RemapDMABuffer(...) function that allocates
DOS memory and avoids 64K boundaries) :)
(If you want the source for GL_RemapDMABuffer() just ask! Programmers,
especially DJGPP users, should GIVE GIVE GIVE!)

"pmode_ptr" is what the caller will use to access the remapped memory
from protected mode
"map_block" is the address (returned by malloc()) on the heap where the
memory is mapped in.

If I free() "map_block", the DOS memory is still remapped (isn't it?)

I was thinking of using dpmi calls to undo it, but I don't know what to
pass as a handle/selector because the __djgpp_memory_handle_list is a
mystery to me.

How to I "unmap" the memory. As I said, it's going into a library, and I
would like to provide a function that un-does this. I am also afraid
that I might leave a dpmi server in a weird state when I exit the
program.

BTW, I WILL NOT use __djgpp_nearptr_enable(). I LIKE SIGSEGV! :)

Thanks.