The driver will halve dmaBuffSizeConfig when in mono mode in dual phase type.

This results in the interrupts being fired 2x as often as expected.

From the TRM:

"Mono: I2S:AIFWMASKx.MASK = 0x01

• Input: Left (0) channel is stored to memory.

• Output: Left (0) channel is fetched from memory and is repeated for the right channel"

This means we shouldn't need to halve the buffer size because only useful samples will be stored by DMA. So the driver should take full advantage of whatever is set in  fixedBufferLength. The h/w will handle ignoring the other samples for us.