MU_XFER_OUT
if ((mu->mu_bufdir & MU_XFER_OUT) != 0) {
#define MC_XFER_OUT MU_XFER_OUT /* Map describes outbound xfer */
mu.mu_bufdir = (wr ? MU_XFER_OUT : MU_XFER_IN);
mu.mu_bufdir = MU_XFER_IN | MU_XFER_OUT;