NCO_CTRL
HSET4(sc, NCO_CTRL(idx), NCO_CTRL_ENABLE);
HCLR4(sc, NCO_CTRL(idx), NCO_CTRL_ENABLE);
ctrl = HREAD4(sc, NCO_CTRL(idx));
HWRITE4(sc, NCO_CTRL(idx), ctrl & ~NCO_CTRL_ENABLE);
HWRITE4(sc, NCO_CTRL(idx), ctrl);