SSCR1_TxTresh
(SSCR1_TxTresh(tx_thres) & SSCR1_TFT);
SSCR1_TxTresh(1) |
SSCR1_TxTresh(TX_THRESH_DFLT);
dma_thresh = SSCR1_RxTresh(RX_THRESH_DFLT) | SSCR1_TxTresh(TX_THRESH_DFLT);
sscr1 |= SSCR1_RxTresh(8) | SSCR1_TxTresh(7);