HDLCDRV_HDLCBUFFER
ret = !((HDLCDRV_HDLCBUFFER - 1 + hb->rd - hb->wr) % HDLCDRV_HDLCBUFFER);
newr = (hb->rd+1) % HDLCDRV_HDLCBUFFER;
newp = (hb->wr+1) % HDLCDRV_HDLCBUFFER;
unsigned short buf[HDLCDRV_HDLCBUFFER];