AC’97 Controller Unit

Figure 13-5. AC’97 Input Frame

Tag Phase Data Phase

 

 

 

 

 

 

 

 

20.8uS

 

 

 

 

 

 

 

 

 

 

 

 

(48 KHz)

 

 

 

 

 

SYNC

12.288 MHz

 

 

 

 

 

 

 

 

 

 

 

 

 

81.4 nS

 

 

 

 

 

 

 

 

 

 

BIT_CLK

 

 

 

 

 

 

 

 

 

 

 

 

 

SDATA_IN

Codec

slot(1) slot(2)

slot(12) "0"

"0"

"0"

19

0

19

0

19

0

19

0

Ready

End of previous

 

 

Time Slot "Valid"

 

 

Slot 1

 

Slot 2

 

 

Slot 3

 

Slot 12

Audio Frame

 

 

 

 

 

 

 

 

 

 

 

Bits

 

 

 

 

 

 

 

 

 

 

 

 

("1" = time slot contains valid PCM data)

 

 

 

 

 

 

 

 

A new audio input frame begins when SYNC transitions from low to high. The low to high transition is synchronous to BITCLK’s rising edge. On BITCLK’s next falling edge, AC’97 samples SYNC’s assertion. This falling edge marks the moment that AC-link’s sides are each aware that a new audio frame has started. The next time BITCLK rises, the ACUNIT transitions SDATA_IN to the first bit position in slot 0 (CODEC ready bit). Each new bit position is presented to AC-link on a BITCLK’s rising edge and then sampled by ACUNIT on the following BITCLK’s falling edge. This sequence ensures that data transitions and subsequent sample points are time aligned for both incoming and outgoing data streams.

Figure 13-6. Start of an Audio Input Frame

 

AC '97 samples SYNC assertion here

SYNC

AC '97 Controller samples first SDATA_IN bit of frame here

BIT_CLK

 

 

SDATA_IN

Codec

slot(1) slot(2)

Ready

End of previous

Audio Frame

The SDATA_IN composite stream is MSB justified (MSB first) and the AC’97 CODEC fills non- valid bit positions with zeroes. SDATA_IN data is sampled on BITCLK’s falling edge.

13.4.2.1Slot 0: Tag Phase

In Slot 0, the first bit is a global bit (SDATA_IN slot 0, bit 15) that indicates whether or not the CODEC is in the CODEC ready state. If the CODEC Ready bit is a 0, the CODEC is not ready for operation. This condition is normal after power is asserted on reset, i.e., while the CODEC voltage references are settling. When the AC-link CODEC Ready indicator bit is a one, the AC-link and AC’97 control and status registers are fully operational. The ACUNIT must probe the CODEC Powerdown Control/Status register to determine which subsections are ready.

Intel® PXA255 Processor Developer’s Manual

13-9

Page 461
Image 461
Intel PXA255 manual Sync