Video Manager Interface (VMI)

The VMAN component relies on a special protocol, called the Video Manager 
Interface (VMI), to receive requests from the translation layers.  VMI 
consists of a small set of operations, each identified by a unique 
function number.  Separate function numbers are required for each 
operation because VMAN exports only one entry point for the translation 
layers to communicate with VMAN. This exported function is called 
VMIEntry.  VMIEntry expects four parameters from each function call it 
receives from a translation layer. 

Because the VMIEntry function receives many different types of requests 
from the translation layers, the gid provides an ID number that identifies 
the GRADD to receive the operation and the ulFunction provides a function 
number that identifies the requested operation.  The last two parameters 
(pIn, pOut) pointer to input and output data structures that are unique to 
each VMI function. 

Most of the requests VMAN receives from a translation layer are passed 
directly to the appropriate GRADD. Each GRADD has its own exported 
function, called HWEntry, which is the same function type as VMIEntry (see 
Graphics Adapter Device Drivers for more information about GHI protocol).