Question: What happens if the external XTAL clock settings in the .cydwr settings and the actual external crystal oscillator frequency are considerably different?
To counter this situation the CPU gets stuck in the Clock Startup procedure. The ClockSetup() phase is associated with a timeout window exceeding, which results in calling the CyClockStartupError().The CPU gets stuck in an infinite while loop within this routine. The routines can be found in cyfitter_cfg.c. Figures 1 and 2 depict the same.
Figure 1. Clock Setup Routine Executed During Startup
Figure 2. Clock Startup Error Routine; by Default This Would Run into an Infinite While Loop