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Bf548 - LCD and AD1980 noise

Question asked by Ostenn on Sep 27, 2012
Latest reply on Oct 4, 2012 by jobo23

Hi,

We're developing an application that uses both the LCD screen and the AD1980 codec and I'm having small compatibility problems that need to be fixed.

Using the Audio Loopback example coupled with the RGB_Out we have developed an application that displays the audio data on the LCD screen in either the time or frequency domains.

The problem is that there is considerable noise in the audio buffer, the music is somewhat audible but there is noise and almost a phaser and bit-crushing effect happening to the sound, when bass occurs the noise amplitude seems to be higher.
This noise stops when the LCD screen is disabled.

 

First I through perhaps it could be memory allocations, but I experimented putting the audio data in various areas of memory and the problem persists.

 

I have briefly looked at DMA priority and rearranged the DMA priority of SPORT0 (Audio) and EPPI0(LCD) in so that the audio interrupt has priority over the LCD, but this didnt seem to have any affect.


The LCD doesn't uses Loopback and not deferred callback.

I have tested this now on multiple Blackfins.

 

Any suggestions, am I missing something?

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