DAQP_FIFO_SIZE
while (nbytes > DAQP_FIFO_SIZE * 3 / 4)
threshold = DAQP_FIFO_SIZE / 2;
outb((DAQP_FIFO_SIZE - threshold) & 0xff,
outb((DAQP_FIFO_SIZE - threshold) >> 8, dev->iobase + DAQP_AI_FIFO_REG);