Int 2F Fn 4B02  - DOS 5+ Task Switcher - Installation Check                [T]

   AX = 4B02h
   BX = 0000h
   ES:DI = 0000h:0000h

Return: ES:DI = 0000h:0000h if task switcher not loaded
   ES:DI -> task switcher entry point (see below) if loaded
       AX = 0000h

Notes: the returned entry point is that for the most-recently loaded task
     switcher; the entry points for prior task switchers may be determined
     with the "get version" call (see below)
   this function is supported by PC Tools v8+ CPTASK

See Also: AX=4A05h,AX=4B03h

Call task switcher entry point with:
   AX = 0000h get version

       Return: CF clear if successful
               AX = 0000h
               ES:BX -> task switcher version struct (see below)
           CF set if unsupported function
   AX = 0001h test memory region
       ES:DI -> first byte to be tested
       CX = size of region to test

       Return: CF clear if successful
               AX = memory type of tested region
               0000h global
               0001h global and local
               0002h local (replaced on session switch)
           CF set if unsupported function
   AX = 0002h suspend switcher
       ES:DI -> new task switcher's entry point

       Return: CF clear if successful
               AX = state
               0000h switcher has been suspended
               0001h switcher not suspended, new switcher must
                   abort
               0002h switcher not suspended, but new switcher
                   may run anyway
           CF set if unsupported function
   AX = 0003h resume switcher
       ES:DI -> new task switcher's entry point

       Return: CF clear if successful
               AX = 0000h
           CF set if unsupported function
   AX = 0004h hook notification chain
       ES:DI -> callback info structure to be added to chain
           (see AX=4B01h)

       Return: CF clear if successful
               AX = 0000h
           CF set if unsupported function
   AX = 0005h unhook notification chain
       ES:DI -> callback info structure to be removed from chain
           (see AX=4B01h)

       Return: CF clear if successful
               AX = 0000h
           CF set if unsupported function
   AX = 0006h query API support
       BX = asynchronous API identifier

       Return: CF clear if successful
               AX = 0000h
               ES:BX -> API info structure (see below) for the
                   client which provides the highest
                   level of
           CF set if unsupported function

Format of task switcher version structure:
Offset Size    Description
 00h   WORD    major version of supported protocol  (current protocol is 1.0)
 02h   WORD    minor version of supported protocol
 04h   WORD    major version of task switcher
 06h   WORD    minor version of task switcher
 08h   WORD    task switcher ID (see AX=4B03h)
 0Ah   WORD    operation flags
       bit 0: set if task switcher disabled
       bits 1-15: reserved (0)
 0Ch   DWORD   pointer to ASCIZ task switcher name
       ("MS-DOS Shell Task Switcher" for DOSSHELL task switcher)
 10h   DWORD   pointer to previous task switcher's entry point or 0000h:0000h

Format of API info structure:
Offset Size    Description
 00h   WORD    size of structure in bytes (000Ah)
 02h   WORD    API identifier
       0001h NetBIOS
       0002h 802.2
       0003h TCP/IP
       0004h LAN Manager named pipes
       0005h Novell NetWare IPX
 04h   WORD    major version \ of highest version of API for which the support
 06h   WORD    minor version / level specified in the next field is provided
 08h   WORD    support level
       0001h minimal support
       0002h API-level support
       0003h switcher compatibility
       0004h seamless compatibility