I am currently looking at using the RTC 32KHz oscillator on an LPC11u68 to run the main clock and when I switch the system PLL source to SYSCTL_PLLCLKSRC_RTC32K the system hangs and I need to use ISP reset to clear the device to reconnect. I have initially got the system running off an external oscillator (also works from IRC oscillator) and then when I try to switch to the slow clock things break.
I am using the LPCOpen library with the following code to switch the main clock:
Chip_Clock_EnablePeriphClock(SYSCTL_CLOCK_RTC); Chip_Clock_EnableRTCOsc(); Chip_Clock_SetMainClockSource(SYSCTL_MAINCLKSRC_PLLIN); Chip_Clock_SetSystemPLLSource(SYSCTL_PLLCLKSRC_RTC32K);
I am using the call to void Chip_SetupXtalClocking(void) to set the initial clock (that seems to work fine).
Is there something I am missing? According to the datasheet, this is all I need to do to use the RTC 32 KHz oscillator for the system clock.