WM8281ECSSLASHR datasheet(198/392 Pages) CIRRUS

198 / 392 page

WM8281

198

Rev 4.0

OUTPUT SIGNAL PATH AEC LOOPBACK

The WM8281 incorporates loopback signal path, which is ideally suited as a reference for Acoustic

Echo Cancellation (AEC) processing. Any of the output signal paths may be selected as the AEC

loopback source.

When configured with suitable DSP firmware, the WM8281 can provide an integrated AEC capability.

The AEC loopback feature also enables convenient hook-up to an external device for implementing

the required signal processing algorithms.

The AEC Loopback source is connected after the respective digital volume controls, as illustrated in

Figure 56. The AEC Loopback signal can be selected as input to any of the digital mixers within the

WM8281 digital core. The sample rate for the AEC Loopback path is configured using the OUT_RATE

within the “Digital Core” section.

The AEC loopback function is enabled using the AEC_LOOPBACK_ENA register. The source signal

for the Transmit Path AEC function is selected using the AEC_LOOPBACK_SRC register.

The WM8281 performs automatic checks to confirm that the SYSCLK frequency is high enough to

support the AEC Loopback function. If an attempt is made to enable this function, and there are

insufficient SYSCLK cycles to support it, then the attempt will be unsuccessful. (Note that any signal

paths that are already active will not be affected under these circumstances.)

The Underclocked Error condition can be monitored using the GPIO and/or Interrupt functions. See

“General Purpose Input / Output” and “Interrupts” for further details.

The AEC_ENA_STS register indicates the status of the AEC Loopback function. If an Underclocked

Error condition occurs, then this bit can provide indication of whether the AEC Loopback function has

been successfully enabled.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R1104

(0450h)

DAC AEC

Control 1

5:2

AEC_LOOPBAC

K_SRC [3:0]

0000

Input source for Tx AEC function

0000 = OUT1L

0001 = OUT1R

0010 = OUT2L

0011 = OUT2R

0100 = OUT3L

0101 = OUT3R

0110 = OUT4L

0111 = OUT4R

1000 = OUT5L

1001 = OUT5R

1010 = OUT6L

1011 = OUT6R

All other codes are Reserved

AEC_ENA_STS

Transmit (Tx) Path AEC Control Status

0 = Disabled

1 = Enabled

AEC_LOOPBAC

K_ENA

Transmit (Tx) Path AEC Control

0 = Disabled

1 = Enabled

Table 69 Output Signal Path AEC Loopback Control

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