Intel PXA255 AC-link Audio Output Frame Sdataout, Supported Data Stream Formats Sheet 2, Sync

AC’97 Controller Unit

Table 13-2. Supported Data Stream Formats (Sheet 2 of 2)

Channel	Slots	Comments
Dedicated	One input slot	Dedicated microphone input stream in support of stereo AEC and
Microphone Input		other voice applications.
I/O Control	One output slot	One slot dedicated to GPOs on the modem CODEC.
I/O Status	One input slot	One slot dedicated to status from GPIs on the modem CODEC.
		Data is returned on every frame.

The ACUNIT provides synchronization for all data transaction on the AC-link. A data transaction is made up of 256 bits of information broken up into groups of 13 time slots and is called a frame. Time slot 0 is called the Tag Phase and is 16 bits long. The other 12 time slots are called the Data Phase. The Tag Phase contains one bit that identifies a valid frame and 12 bits that identify the time slots in the Data Phase that contain valid data. Each time slot in the Data Phase is 20 bits long.

A frame begins when SYNC goes high. The amount of time that SYNC is high corresponds to the Tag Phase. AC’97 frames occur at fixed 48 kHz intervals and are synchronous to the 12.288 MHz bit rate clock, BITCLK.

The ACUNIT and the CODEC use the SYNC and BITCLK to determine when to send transmit data and when to sample receive data. A transmitter transitions the serial data stream on each rising edge of BITCLK and a receiver samples the serial data stream on each falling edge of BITCLK. The transmitter must tag the valid slots in its serial data stream. The valid slots are tagged in slot 0.

Serial data on the AC-link is ordered most significant bit (MSB) to least significant bit (LSB). The Tag Phase’s first bit is bit 15 and the first bit of each slot in Data Phase is bit 19. The last bit in any slot is bit 0.

Figure 13-2shows Tag and Data Phase organization for the ACUNIT and the CODEC. The figure also lists the slot definitions that the ACUNIT supports.

Figure 13-2. AC’97 Standard Bidirectional Audio Frame

Slot # 0 1 2 3 4 5 6 7 8 9 10 11 12

SYNC

OUTGOING STREAMS

TAG

CMD

CMD

PCM

PCM

MDM CDC

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

I/O control

ADR

DATA

LEFT

RIGHT

INCOMING STREAMS

TAG

STATUS

STATUS

PCM

PCM

MDM CDC

MIC

RSRVD

RSRVD

RSRVD

RSRVD

RSRVD

I/O Status

ADR

DATA

LEFT

RIGHT

Tag Phase

Data Phase

13.4.1AC-link Audio Output Frame (SDATA_OUT)

The audio output frame data stream corresponds to the multiplexed bundles that make up the digital output data that targets the AC’97 DAC inputs and control registers. Each audio output frame supports up to twelve 20-bit outgoing data time slots. The ACUNIT does not generate samples larger than 16 bits. The four least significant bits are padded with zeroes.

13-4 Intel® PXA255 Processor Developer’s Manual