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Inside Macintosh: Devices /

Chapter 1 - Device Manager / Device Manager Reference

Device Manager Functions / Controlling and Monitoring Device Drivers

PBControl

You can use the PBControl function to send control information to a device driver.

pascal OSErr PBControl(ParmBlkPtr paramBlock, Boolean async); 

paramBlock

A pointer to a CntrlParam structure of the Device Manager parameter block.

async

A Boolean value that indicates whether the request is asynchronous.

-->	ioCompletion	ProcPtr	A pointer to a completion routine.
<--	ioResult	OSErr	The device driver's result code.
-->	ioVRefNum	short	The drive number.
-->	ioCRefNum	short	The driver reference number.
-->	csCode	short	The type of control call.
-->	csParam	short[11]	The control information.

DESCRIPTION

The PBControl function sends information to the device driver specified by the ioCRefNum field. The value you pass in the csCode field and the type of information in the csParam field are defined by the driver you are calling. For more information, see the appropriate chapters for the standard device drivers in this book and other books in the Inside Macintosh series.

SPECIAL CONSIDERATIONS

Do not call the PBControl function synchronously at interrupt time. Synchronous requests at interrupt time may block other pending I/O requests and cause the Device Manager to loop indefinitely while it waits for the device driver to complete the interrupted requests.

ASSEMBLY-LANGUAGE INFORMATION

The trap macro for the PBControl function is _Control (0xA004). Set bit 10 of the trap word to execute this routine asynchronously. Set bit 9 to execute it immediately.

You must set up register A0 with the address of the parameter block. When _Control returns, register D0 contains the result code. Register D0 is the only register affected by this routine.

Registers on entry
A0	Address of the parameter block

Registers on exit
D0	Result code

RESULT CODES

noErr	0	No error
controlErr	-17	Driver does not respond to this control request
badUnitErr	-21	Driver reference number does not match unit table
unitEmptyErr	-22	Driver reference number specifies a nil handle in unit table
abortErr	-27	Request aborted by KillIO
notOpenErr	-28	Driver not open

SEE ALSO

For information about the high-level function for controlling device drivers, see the description of the Control function on page 1-75. For an example of how to send control information to a device driver using the PBControl function, see Listing 1-5 on page 1-23.