Int 2F Fn 0802  U - Driver.sys Support - Execute Device Driver Request  (Cont.)

       Note:   must be called in the context of the process which
             called CritEnter on the semaphore

Note:  the DWORD pointing at the request queue must be allocated by the driver
     and initialized to 0000h:0000h.  It always points at the next request
     to be executed

Format of character queue:
Offset Size    Description
 00h   WORD    size of queue in bytes
 02h   WORD    index of next character out
 04h   WORD    count of characters in the queue
 06h  N BYTEs  queue buffer