SAMA5D4 Xplained Ultra with a Wolfson WM8904 Codec

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brian_
Posts: 15
Joined: Mon Jan 09, 2017 11:59 am

SAMA5D4 Xplained Ultra with a Wolfson WM8904 Codec

Mon Feb 27, 2017 6:04 pm

Hi All,

We are currently trying to use a Wolfson WM8904 Codec with our SAMA5D4 Xplained Ultra devkit and are running in to a few issues - hopefully someone has some input for the following:

Our settings are as follows:

recording settings: arecord -t wav -c 2 -f S16_LE -r 28000 -d 10 grab.wav
input to ADC: Tone generated by a signal generator

When we try to record audio using alsa, the record seems to succeed, however on playback we get some audio anomalies. These anomalies seem to only occur at recording frequencies below 28khz.

The symptoms are as follows:

1) During the recording we can see 3 distinct steps in the frequency of BCLK. During playback of the recording this distorts the tone. During this time we do not see any communication via i2c.

2) After a random time, during either recording or playback, we lose the i2c comms with the wolfson codec. We get i2c timeout errors, and it appears the WM8904 is holding the bus during this time. A restart of the codec seems to clear the issue temporarily, without a restart of the SAMA5D4.



We also have a question regarding the interrupt line that we can see on the schematic for the SAMA5D4-EK dev kit (that has the WM8904 included):

3) On the dev kit there is a interrupt line coming from the codec (Pin 1, IRQ/GPIO1) to the SAMA5D44 on the SAMA5D4-EK board. We do not see any activityof the interrupt pin on the codec when we are using it with the SAMA5D4 Xplained Ultra - is this pin necessary? We also do not see it referenced in the driver.
blue_z
Location: USA
Posts: 1507
Joined: Thu Apr 19, 2007 10:15 pm

Re: SAMA5D4 Xplained Ultra with a Wolfson WM8904 Codec

Wed Mar 01, 2017 1:10 am

brian_ wrote:These anomalies seem to only occur at recording frequencies below 28khz.
That's poorly worded, and therefore confusing.
Is this "frequency" you refer to the sampling rate or the frequency of the (sinusoidal?) waveform being sampled?
brian_ wrote:We also have a question regarding the interrupt line that we can see on the schematic for the SAMA5D4-EK dev kit (that has the WM8904 included):

3) On the dev kit there is a interrupt line coming from the codec (Pin 1, IRQ/GPIO1) to the SAMA5D44 on the SAMA5D4-EK board. We do not see any activityof the interrupt pin on the codec when we are using it with the SAMA5D4 Xplained Ultra - is this pin necessary? We also do not see it referenced in the driver.
You need to read the Wolfson datasheet on use of this interrupt.
It's not needed for basic playback or recording.

Regards

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