Bits 10 - 7, AUD3 - 0, are assigned to the audio channels. They are called AUD3, AUD2, AUD1, and AUD0 and are assigned to channels 3, 2, 1, and 0, respectively. This level 4 interrupt signals "audio block done." When the audio DMA is operating in automatic mode , this interrupt occurs when the last word in an audio data stream has been accessed. In manual mode , it occurs when the audio data register is ready to accept another word of data. See Chapter 5, "Audio Hardware," for more information about interrupt generation and timing .