Video Helper Functions

VMAN exports a number of helper services that GRADDs may use for common 
required functions.  By using video helpers, a GRADD can avoid operating 
system specific calls.  These helper functions are described below: 

The VHAllocMem helper returns a 32-bit pointer to a piece of memory. The 
caller of this function supplies the byte count required. 

The VHFreeMem helper frees memory that has been allocated via the 
VHAllocMem helper. 

The VHLockMem helper makes code or data segments available for ring 0 
interrupt-time processing. 

The VHPhystoVirt helper converts physical address ranges to linear virtual 
address ranges for processes using VMI. 

The VHMap helper aliases process memory to a global ring 0 context. 

The VHMapVRAM helper converts the physical address of VRAM to linear 
virtual aperture for both process and global ring 0 context.