The FIFO can be read by polling mode and interrupt mode. during interrupt mode, once the fifo water or full interrupt is triggered,there are data in the fifo. the fifo length will not be 0. during polling mode, make sure that the accessing fifo interval is grater than one frame. which mode are you using? can you record the normal working flow by salea logic analyzer then upload to the community? if lucky, better to upload the waveform while issue happens.
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