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Inside Macintosh: Networking /

Chapter 5 - AppleTalk Data Stream Protocol (ADSP) / ADSP Reference

Routines / Maintaining an ADSP Connection and Using It to Exchange Data

dspAttention

The dspAttention routine sends an attention code and an attention message to the remote connection end. You use the PBControl function to call the dspAttention routine. See "Routines" on page 5-43 for a description of the PBControl function.

-->	ioCompletion	ProcPtr	A pointer to a completion routine.
<--	ioResult	OSErr	The function result.
-->	ioCRefNum	Integer	The driver reference number.
-->	csCode	Integer	Always dspAttention for this function.
-->	ccbRefNum	Integer	The CCB reference number.
-->	attnCode	Integer	The client attention code.
-->	attnSize	Integer	The size of attention data in bytes.
-->	attnData	Ptr	A pointer to attention data.

Field Description

csCode

The routine selector, always dspAttention for this routine.

ccbRefNum

The connection control block (CCB) reference number that the dspInit routine returned.

attnCode

The 2-byte attention code that you wish to send to the remote connection end. You can use any value from $0000 through $EFFF for the attention code. The values $F000 through $FFFF are reserved for use by ADSP.

attnSize

The size in bytes of the attention message you wish to send.

attnData

A pointer to the attention message. The attention message can be any size from 0 through 570 bytes. There are no restrictions on the content of the attention message.

DESCRIPTION

The dspAttention routine sends an attention code and message. Attention codes and attention messages can have any meaning that your application and the application at the remote connection end both recognize. The purpose of attention codes and messages is to allow clients of ADSP to send messages outside the normal data stream.

For example, if a connection end on a mainframe computer is connected to several connection ends in Macintosh computers being used as remote terminals, the mainframe computer might wish to inform the remote terminals that all connections will be terminated in ten minutes. The mainframe application could send an attention message to each of the remote terminals informing them of this fact, and the terminal emulation programs in the Macintosh computers could then display an alert message on the screen so that the users could prepare to shut down.

ASSEMBLY-LANGUAGE INFORMATION

To execute the dspAttention routine from assembly language, call the _Control trap macro with a value of dspAttention in the csCode field of the parameter block.

RESULT CODES

noErr	0	No error
errAttention	-1276	Attention message too long
errState	-1278	Connection is not open
errAborted	-1279	Request aborted by dspRemove or dspClose routine
errRefNum	-1280	Bad connection reference number