National Semiconductor Advanced Audio Interface

The Advanced Audio Interface (AAI) provides a full-duplex, serial, synchronous interface to codecs and similar serial devices. It is the same Advanced Audio Interface proven in high-volume devices from National Semiconductor and is available exclusively from IPextreme as synthesizable IP..

The host interface of the AAI complies with the AMBA 2.0 APB protocol. Control registers provide CPU control of operating mode, data word length, shift clock and frame sync generation, FIFO threshold levels, transmit/receive slot assignment in Network mode, and enabling/disabling interrupts. Status registers provide interrupt and FIFO status.

Transfer of audio data between the AAI and the host system can be either interrupt-driven or through DMA to reduce CPU utilization. When configured for interrupt-driven operation, the AAI buffers the audio data in 16-word receive and transmit FIFOs. When configured for DMA, the AAI buffers the audio data in registers.

The transmit and receive paths can operate either asychronously or synchronously to each other. Each path uses a three-wire serial interface to the external codec: shift clock (STCLK/SRCLK), frame sync (STFS/SRFS), and data (STD/SRD).

In Asynchronous mode, the transmit and receive paths each use their respective shift clock and frame sync signals. In Sychronous mode, the transmit and receive paths both use the transmit shift clock and frame sync signals; the receive shift clock and frame sync signals then function as auxiliary frame sync signals (SFS1 and SFS2) to enable addressing of multiple codecs in Network mode.

To reduce chip-level pin count, the interface signals to the external codec can be shared with other on-chip functions through a General Purpose I/O (GPIO) Controller.