Specifications

CHAPTER 4

Software Support

78 Gestalt Selector

called at interrupt time with interrupts turned off. It can use registers AX, BX, CX, DX,

DI, SI, ES, and DS.

The completion routine for the MsgPBlk structure returned by the receive procedure is

called at interrupt time and can use registers AX, BX, CX, DX, DI, SI, ES, and DS. You

must save all other registers. ES:BX must also contain a pointer to the MsgPBlk structure.

Removing a Message Handler 4

Message handlers can be called until they are removed. Before your application

terminates, you must remove the handler so that the interface driver will not call it after

the application has terminated.

Removing a Message Handler on the Mac OS 4

To remove a message handler on the Mac OS, your application makes an appropriate

control call to the interface driver and passes the driver a pointer to the handler. The

message control code is rsRemoveMsgHandler = 802.

Parameter block

—> indicates input to the driver

<— indicates output from the driver

Removing a Message Handler on the PC System 4

To remove a message handler on the PC system, your application makes a call to

INT 5Fh with AH = 3 and with a pointer to the MsgRecElem record in registers ES:BX.

Gestalt Selector 4

The Gestalt function enables you to obtain information about software or hardware

components available on your system. The original Gestalt Manager consists of three

functions—Gestalt, New Gestalt, and Replace Gestalt. These functions are described in

Inside Macintosh, Volume VI, in the section “Using the Gestalt Manager.”

12” and 7” cards have an added Gestalt function. This is a Public Gestalt selector that

enables you to determine the state of certain features associated with the PC system. The

longword bit ﬁeld result is a 32-bit four-character selector. The four characters are

—> ioCompletion long Pointer to the completion routine.

<— ioResult word Device driver’s result code.

—> ioRefNum word Device driver’s reference number.

—> csCode word Equals rsRemoveMsgHandler.

—> csParam+0 long Pointer to MsgRecElem.