PREV_RX
#define PREV_RX(i) (((i) - 1) & (SEEQ_RX_BUFFERS - 1))
#define PREV_RX(num) (((num) - 1) & (RX_RING_SIZE - 1))
#define PREV_RX(num) (((num) - 1) & (RX_RING_SIZE - 1))
#define PREV_RX(num) (((num) - 1) & (RX_RING_MAXSIZE - 1))