Memory mapped devices such as network adapters and displays sometimes have memory mapped at physical addresses that lie outside of the normal 1Mb of memory that is addressable in real mode. Under many implementations of DPMI, all addresses are linear addresses since they use the paging mechanism of the 80386. This service can be used by device drivers to convert a physical address into a linear address. The linear address can then be used to access the device memory.
Some implementations of DPMI may not support this call because it could be used to circumvent system protection. This call should only be used by programs that absolutely require direct access to a memory mapped device.
AX = 0800h BX:CX = Physical address of memory SI:DI = Size of region to map in bytes
If function was successful: Carry flag is clear. BX:CX = Linear address that can be used to access the physical memory If function was not successful: Carry flag is set.