Servicing McASP with FIFO and no DMA

I am trying to transmit data to the McAsp using the FIFO but without DMA. I am able to configure and enable the FIFO and even fill it with 64 words of information. But when I enable the McAsp, it immediately generates an underun error. I verify that the FIFO is full, but nothing I have tried will get the McAsp to use the FIFO data. Any ideas?

Thanks,

Michael