How can I get physical address memory from logical address memory?

Hi!
I need to allocate memory and I used malloc, but the problem is that I get only the logical address of memory. How can I get the corresponding physical memory?

Thanks
Pedro Fernandes

You can't, because it's virtual memory in modern OS. Why you need it at all?

My problem is that I have to configure DMA of the DS3134 (Chateau - Channelized T1 and E1 And Universal HDLC Controller) and it only works with the physical address memory. I can't pass logical addresses to it.

You have to be in kernel mode and use corresponding functions. malloc isn't appropriate for you( I suppose, that we are speaking about NT )

If you really want to access physical memory on
your system, use this method. This code is sure
to break your program if you do not know 100% how the physical
circuitry of your computer works.
If you know the physical address of the memory buffer, you must obtain an address that you can physically access.Windows NT is a virtual memory operating system, requiring us to map the physical address. This is a two-step process


m_nBufferMemorySize = 4 * 1024 * 1024;
m_pLAW = (unsigned char *)VirtualAlloc(
0,
m_nBufferMemorySize,
MEM_RESERVE,
PAGE_NOACCESS);
VirtualCopy(m_pLAW,
(LPVOID)(m_nLAWPhysical>>8),
m_nBufferMemorySize,
PAGE_READWRITE|PAGE_NOCACHE|PAGE_PHYSICAL);

First, reserve space in the virtual address space for the size of the mapped region, in this case 4MB, using VirtualAlloc. This is equivalent to saving a contiguous range of addresses within the 4GB virtual address range. Next, use the function VirtualCopy to set the page table entries to map the physical frame buffer address in m_nLAWPhysical into the reserved address range. The variable m_pLAW can now be used to directly access the frame buffer and memory-mapped registers on the chip. You can now read and write to physical RAM.

The library that contains the VirtualCopy function is not available on all
releases of Visual C++. So look around for it.

You may consult the Articles in the Win2000 Device Driver Kit:
Virtual Device Drivers\...\Memory-Mapped IO, and
Virtual Device Drivers\...\DMA

clem