INT 31H 0800H: Physical Address Mapping

                                                    Compatibility: DPMI 0.9+ 
 Expects: AX    0800H
          BX:CX physical address of memory
          SI:DI size of region to map, in bytes
 Returns: CF    NC (clear) if successful; else AX = DPMI Error Code
          BX:CX linear address usable to access physical memory
    Info: This converts a physical address into a linear address.

          This allows device drivers to access device-defined memory
          addresses above 1 MB such as the Weitek math chip (usually mapped
          at 3 GB) or hardware such as video coprocessors' memory aperture.

See Also: DPMI API
          INT 2fH: Multiplex Interrupt
          DOS Functions