ZYNQUART_RING_SIZE
#ifndef ZYNQUART_RING_SIZE
u_int zynquart_rbuf_size = ZYNQUART_RING_SIZE;
u_int zynquart_rbuf_hiwat = (ZYNQUART_RING_SIZE * 1) / 4;
u_int zynquart_rbuf_lowat = (ZYNQUART_RING_SIZE * 3) / 4;