Inside Macintosh: Sound /

Chapter 3 - Sound Input Manager / Sound Input Manager Reference

Application-Defined Routines / Sound Input Interrupt Routines

MySIInterruptRoutine

A sound input interrupt routine has the following syntax:

PROCEDURE MySIInterruptRoutine;

DESCRIPTION

A sound input device driver executes the sound input interrupt routine associated with an asynchronous sound recording whenever the driver's internal buffers are full. The internal buffers contain raw samples taken directly from the input device. The interrupt routine can thus modify the samples in the buffer in any way it requires. After your sound input interrupt routine finishes processing the data, the sound input device driver compresses the data (if compression is enabled) and copies the data into your application's buffer.

SPECIAL CONSIDERATIONS

If your sound input interrupt routine accesses your application's global variables, it must ensure that the A5 register contains the address of the boundary between the application global variables and the application parameters. Your application can pass the value of the A5 register to the sound input interrupt routine in the userLong field of the sound input parameter block. For more information on ensuring the validity of the A5 register, see the chapter "Memory Management Utilities" in Inside Macintosh: Memory.

ASSEMBLY-LANGUAGE INFORMATION

Sound input interrupt routines are sometimes written in assembly language to maximize real-time performance in recording sound. On entry, registers are set up as follows:

Registers on entry
A0	Address of the sound parameter block passed to SPBRecord
A1	Address of the start of the sample buffer
D0	Peak amplitude for sample buffer if metering is on
D1	Size of the sample buffer in bytes

If you write a sound input interrupt routine in a high-level language like Pascal or C, you might need to write inline code to copy variables from the registers into local variables that your application defines.

Because a sound input interrupt routine is called at interrupt time, it must preserve all registers.