VxD_IO

include vmm.inc

VxD_IO  Port, IOCallback

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.

No return value.

Port: Number of the I/O port to be trapped.
IOCallback: Name of the I/O callback procedure. For information about the callback procedure, see below.

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. In such case, the I/O callback procedure can use the EDX register to determine which port was accessed by the virtual machine.

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
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.
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.
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.
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. (Client_ECX if Addr_32_IO is set.)
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.
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.
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.

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.

The Data parameter is used only when I/O type is for output.

VxD_IO

See Also