The SmartFusion2 devices, except M2S050, have an auxiliary crystal oscillator dedicated to real-time clocking as an alternative source for the 32 kHz clock. The RTC can take its 32 kHz clock source from the auxiliary crystal oscillator when the main crystal oscillator is being used.
Similar to the main crystal oscillator, the auxiliary crystal oscillator can work with an external crystal, ceramic resonator, or an RC circuit to generate a high-precision clock in the range of 32 kHz to 20 MHz. There are two I/O pads for connecting the external frequency source to the auxiliary crystal oscillator: XTLOSC_AUX_EXTAL and XTLOSC_AUX_XTAL. The output frequency range, operating modes, and characteristics for the auxiliary crystal oscillator are the same as those for the main crystal oscillator.
For detailed information, see UG0449: SmartFusion2 and IGLOO2 Clocking Resources User Guide.