DevHelp VirtToPhys

This service converts a selector:offset pair to a 32-bit physical address.

Syntax

C

USHORT APIENTRY DevHelp_VirtToPhys( PVOID   SelOffset,
                                    PULONG  PhysAddr)

Assembler

LDS   SI,address              ; Virtual address:
                              ; selector:offset
MOV   DL,DevHlp_VirtToPhys

CALL  [Device_Help]

Parameters

C

SelOffset (PVOID) 

Virtual address (selector:offset)

PhysAddr (PULONG) 

Physical address to be returned.

Assembler

LDS   SI,address              ; Virtual address:
                              ; selector:offset

Return Code

C

Success Indicator: 0

Returns 32-bit physical address.

Possible errors: None.

Assembler

 'C' Clear if successful.
       AX:BX = Physical address:  32-bit number.

Remarks

If the segment is not already known to be locked, the virtual address should be locked using the DevHlp_Lock before this service is called. VirtToPhys is typically used to convert a virtual address. The virtual address is supplied to the physical device driver by a process (through a generic IOCtl), to a physical memory address so the memory can be accessed at interrupt time.

Example Code

C

#include  "dhcalls.h"

USHORT APIENTRY DevHelp_VirtToPhys( PVOID   SelOffset,
                                    PULONG  PhysAddr)