Analog Discovery I2S Analyzer Trouble Shooting

[Wayne Chen]

Hi Sirs,

Good Day! I am a new user of Analog Discovery 2. I hit a roadblock when learning the process to acquire I2S with the following steps. 

1. Sent 0dBFS, 1kHz sinewave with 48kHz sample rate, 24bit, 64*fs (3.072MHz BCLK) from Audio Precision APX500 to Analog Discovery 2.

     
 

2. Programmed AD2's DIOs to correspond I2S format. However, the reconstructed signals were discontinuous and distorted.  

      

    

    

     
3. According to the recorded stream, the sample rate of LRCK looked unstable. It was not helpful by increasing sample rate from 10MHz to 20MHz. 

    

    

    

Would you please provide tips to acquire I2S data stream properly and advise the maximum I2S speed does AD2 support? I assumed that the AD2 can reconstruct 1kHz sine waves.
Was it a hardware limitation or my software configuration problem? Please do not hesitate to inform me if there is any missing or mistake.

Thank you and Best regards,

Wayne Chen
06/04/2020  

[attila]

Hi @Wayne Chen

In order to capture the highest frequency signal you need at least double of capture sample rate.
If your bit clock is 3.072MHz (32bit word * 2 * 48kHz) you will need at least 6.25MHz sample rate.

At such high continuous signal rate the AD2 can only be used in Repeated mode.
The Record mode needs to stream data over USB and it can do at most at 1-2MHz continuous signal rate.
For burst signals (UART,SPI...) the data compression helps to be able to record at higher rates, but not in case of continuous I2S stream.

In device manager you can select the 4th device configuration to have more device buffer for Logic Analyzer.

[Wayne Chen]

Hello Attila,

Thank you for supporting. I can get better waveforms with the 4th configuration:

    

However, I saw a GUI problem with reconstructed wave forms which needs a workaround:

I specified data format of "Decimal" to Channel Left and "Signed" to Channel Right.
Data format of "Signed" is important for us to reconstruct I2S signals, however, we cannot see valid wave forms as the pictures below: 

    


    
 
The GUI plots redundant tri-angles on non-used slots which makes the wave forms hard to read.The GUI should keeps reconstructed signal flat in those non-used slots.  
 
     

      

If you have any comment, please do not hesitate to inform me.

Thank you and Best regards,

Wayne Chen
06/05/2020

[attila]

Hi @Wayne Chen

Probably the data format is the commonly used Two's complement signed. The simple Signed format refers to MSB sign | value.
Could you attach or send to me a workspace with captured data?

The latest beta version fixes the zigzag in analog curve for signed formats:
https://forum.digilentinc.com/topic/8908-waveforms-beta-download/

 

[Wayne Chen]

Hello Attila,

Thank you for your advise. I saw zigzag problem with 2's complement signed as well. Test result of beta version 3.13.18 will follow.

My test was done by WaveForms Ver 3.12.2

Attached files are my work space and acquisition stream of 1kHz, 0dBFS sine wave. Left = Decimal format, Right = 2's complement format

Thank you and Best regards,

Wayne Chen
06/05/2020

 

I2S Acquisition Project.dwf3logic.zip I2S_Test_Acquisition.dwf3logicacq.zip

[attila]

Hi @Wayne Chen

The data is Two's complement.

[Wayne Chen]

Thank you for your advise, Attila.

I can get good reconstructed I2S signals with the newly GUI ver 3.13.18 now.



Wayne Chen
06/05/2020