SS_TXFIFO
readsl(ss->base + SS_TXFIFO, mo.addr + oo, todo);
readsl(ss->base + SS_TXFIFO, mo.addr + oo, todo);
readsl(ss->base + SS_TXFIFO, ss->bufo, tx_cnt);
readsl(ss->base + SS_TXFIFO, data, len / 4);