SSCR0_SCR
reg = SSCR0_SCR(CLOCK_DIV_10MHZ);
sscr0 &= ~SSCR0_SCR(0xfff);
sscr0 |= SSCR0_SCR(CLOCK_DIV_10MHZ);
sscr0 |= SSCR0_SCR(howmany(MAX_CLOCK_RATE, min(MAX_CLOCK_RATE, clock)));