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include vmm.inc
 
VxD_IO  Port, IOCallback
 
The VxD_IO macro adds an I/O callback procedure and I/O port number to an
I/O table. Virtual devices use the macro in conjunction with the
Begin_VxD_IO_Table and End_VxD_IO_Table macros to create a table of I/O
callback procedures for the Install_Mult_IO_Handlers service.
 
Parameter   Description
────────────────────────────────────────────────────────────────────────────
 
Port        Specifies the number of the I/O port to be trapped.
 
IOCallback  Specifies the name of the I/O callback procedure. See the
            Comments section for information about this procedure.
 
Return Value
 
This service has no return value.
 
Comments
 
The I/O table can contain any number of VxD_IO macros. Each macro must
specify an unique I/O port number, but the same I/O callback procedure can
be assigned to more than one port.
 
After a virtual device installs the callback procedures, the system calls a
procedure whenever a program in the virtual machine attempts to access the
corresponding port. The system calls the procedure as follows:
 
mov     ebx, VM             ; current VM handle
mov     ecx, IOType         ; type of I/O
mov     edx, Port           ; port number
mov     ebp, OFFSET32 crs   ; points to a Client_Reg_Struc
mov     eax, Data           ; output data (if I/O type is output)
call    [IOCallback]
 
mov     [Data], eax         ; input data (if I/O type is input)
 
The VM parameter specifies the current virtual machine, Port specifies the
I/O port, and crs points to a Client_Reg_Struc structure containing the
register contents for the current virtual machine.
 
The IOType parameter specifies the type of input or output operation
requested and determines whether the callback procedure receives data in the
EAX register or must return data in the EAX register. The IOType parameter
can be a combination of the following values:
 
Value         Meaning
────────────────────────────────────────────────────────────────────────────
Byte_Input    Input a single byte; place in AL if String_IO not given.
 
Byte_Output   Output a single byte from AL if String_IO not given.
 
Word_Input    Input a word; place in AX if String_IO not given.
 
Word_Output   Output a word from AX if String_IO not given.
 
Dword_Input   Input a double word; place in EAX if String_IO not given.
 
Dword_Output  Output a double word from EAX if String_IO not given.
 
String_IO     Input or output a string. The high 16-bits specifies segment
              address of buffer containing the string to output or to
              receive the string input.
 
Rep_IO        Repeat the input or output string operation the number of
              times specified by the Client_CX field in the
              Client_Reg_Struc structure.
 
Addr_32_IO    Use 32-bit address offsets for input or output string
              operations. If this value is not given, the 16-bit offsets are
              used.
 
Reverse_IO    Decrement string address on each input or output operation. If
              this value is not given, the string address is incremented on
              each operation.
 
In memory, an I/O table consists of a VxD_IOT_Hdr structure followed by one
or more VxD_IO_Struc structures. The first word in the table specified the
number of entries. Each entry consists of a word specifying the port number
and a double word specifying the 32-bit offset of the callback procedure.
 
See Also
 
Begin_VxD_IO_Table, End_VxD_IO_Table, Install_Mult_IO_Handlers
 
 
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