Specifications

CHAPTER 4

Software Support

Passing Messages 73

calling the driver with a 32-bit selector that is deﬁned in both applications and with a

count of the number of messages to be used by the applications. The interface driver

allocates a range of messages for that selector and returns the base command number to

the caller. The interface driver makes sure that both the PC application and the

Macintosh application registering messages under the same selector will receive the

same base command number.

Registering Messages From the Mac OS 4

To register your messages from a Macintosh application, make an

rsRegisterMessage control call with the message selector in csParam+0 and the

number of message commands to allocate in csParam+4.

The routine that registers message type is rsRegisterMessage = 803.

Parameter block

—> indicates input to the driver

<— indicates output from the driver

<—> indicates bidirectional transfer (input and output)

The interface driver returns the base command number in csParam+0. If the interface

driver cannot allocate the messages, an error code is returned in ioResult.

Registering Messages From the PC System 4

To register your messages from a PC application, load the 32-bit selector into register

EBX and the message count into register CX. Then call INT 5Fh with AH = 4. The

interface driver returns the base command number in register BX. Register AH contains

an error code if the message could not be allocated.

Sending a Message 4

To send a message, you must pass a message parameter block (MsgPBlk) to the interface

driver. The rsSendMessage routine is always asynchronous. The message control code

for sending a message is rsSendMessage = 800. This routine simply queues the

message parameter block and returns to the caller. The msgResult ﬁeld is set to 1 (busy)

until the message has been sent.

—> ioCompletion long Pointer to the completion routine.

<— ioResult word Device driver’s result code.

—> ioRefNum word Device driver’s reference number.

—> csCode word Equals rsRegisterMessage.

<—> csParam+0 long 32-bit message selector.

—> csParam+4 long Number of message commands to allocate.