Int 2F Fn 4A10  - Smartdrv V4.00+ - Status                                 [c]

   AX = 4A10h
   BX = 0003h
   BP = drive # (0=A, 1=B, etc.)
   DL = subfunction
       00h only get information
       01h turn on read cache
       02h turn off read cache
       03h turn on write cache
       04h turn off write cache

Return: AX = BABEh if OK
   DL = status
       bit 7  not cached
       bit 6  write-through (not write-cached)
       bit 5  ???
       bits 0-4 drive # (0=A, 1=B...)
   DL = FFh if drive does not exist

Notes: If the read cache is off, reads will not be cached, but writes will
     continue to be cached if the write-cache is enabled.
   this function is also supported by PC-Cache v8.0.

See Also: AX=4A10h/BX=0000h