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From:	shwonder AT gmail DOT com
Newsgroups:	comp.os.msdos.djgpp
Subject:	How to unmap memory, mapped by __djgpp_map_physical_memory
Date:	Thu, 21 Jun 2007 06:40:24 -0700
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To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

Hi, All

I map device memory into virtual address space using
__djgpp_map_physical_memory(). Is there a way to unmap it back. For
example:

void* AllocateDeviceMemory(unsigned long physicalAddress, unsigned
long size)
{
    /* disable interrupts */
    bool bInterrupts = disable();

    /* align size to page boundary */
    (size += 0x0FFF) &= ~0x0FFF;

    /* allocate page aligned buffer in a heap */
    void* virtualAddress = valloc(size);

    /* Has valloc succeed? */
    if (!virtualAddress) return NULL;

    /* map virtual buffer to physical memory */
    if (__djgpp_map_physical_memory(virtualAddress, size,
physicalAddress) == 0) {
        __dpmi_meminfo info;
        info.address = (unsigned)virtualAddress +
__djgpp_base_address;
        info.size = size;
        /* lock region */
        if (__dpmi_lock_linear_region(&info) == 0) {

            /* restore interrupts flag */
            if (bInterrupts) enable();

            return virtualAddress;
        }
    }
    /* free allocated buffer */
    /* NOTE, virtual memory still remains mapped to device
address !!!!! */
    /* HOW CAN WE AVOID THIS ??? */
    free(virtualAddress);

    /* restore interrupts flag */
    if (bInterrupts) enable();

    return NULL;
}

void FreeDeviceMemory(void* virtualAddress)
{
    __dpmi_meminfo info;
    info.address = (unsigned)virtualAddress + __djgpp_base_address;
    info.size = size;
    /* unlock region */
    __dpmi_unlock_linear_region(&info);

    /* free allocated buffer */
    /* NOTE, virtual memory still remains mapped to device
address !!!!! */
    /* HOW CAN WE AVOID THIS ??? */
    free(virtualAddress);
}


How can we restore page mappings, for mapped pages (see
FreeDeviceMemory() for example) ?

Thanks.

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