Details:

The internal 10MHz RC oscillator serves as a safety monitor for the XTAL clock, detecting its presence or absence as described in the Limp Mode section of the TRM. In the event of XTAL failure, the device automatically switches to RC_CLK to maintain operation of the CPU and peripherals. Since the RC oscillator's accuracy is not comparable to the XTAL, it can only detect whether the XTAL clock is present (toggling) or absent—it cannot verify the accuracy or frequency precision of the XTAL clock.

Enabling Limp Mode:

• Limp Mode is disabled by default and must be explicitly enabled by software
• XTAL clock loss detection: Set LIMP_MODE_EN_XTALCLK_LOSS_EN bits in MSS_TOPRCM_LIMP_MODE_EN register.

Workaround(s):

If monitoring the accuracy of the XTAL clock or PLL clock is required, an external high-accuracy reference clock must be provided to the MCU. The DCC (Dual Clock Comparator) module can then be configured to use this external reference clock to verify the accuracy of the XTAL or PLL clocks.