Dear Sir,
We have a serious problem with OMAP-L137 EVM. I intend to check the SNR specification of the audio codec on this board. Focusing on this issue, I generated a sinusoid wave by a signal generator and fed it to the Line in input of the board. Then I use the following command on the ARM to record and play the audio on the Line out:
arecord -d 20 -D 'hw:0,0' -r 96000 -f S32_LE -c 2 | aplay -D 'hw:0,0' -c 2
The input and output waves are shown in Figure 1 and figure 2 respectively. The output is so noisy. The noise is in-band noise. I checked it.
(Figure 1)
(Figure 2)
The audio codec group said that check the MCLK and WCLK clocks of the codec. Figure 3 shows the WCLK clock. It seems to be good.
(Figure 3)
I saw a strange thing happened on MCLK. Figure 4 and Figure 5 shows the MCLK when I start the board for first time.The Linux kernel is loaded. All things seem to be good. HOWEVER, when I start recording and playing with the audio codec, the MCLK changes. Figure 6, Figure 7, and Figure 8 show the MCLK after using Audio Codec. Wowwww! It does not seem to be NORMAL. We have threeOMAP-L137 boards and all have the same problem. The version of our boards is " I ". you can check this Problem easily.
(Figure 4)
(Figure 5)
(Figure 6)
(Figure 7)
(Figure 8)
I would be very thankful if you can help me.
Jack,