12.4.7.5.2 Low Frequency Drift Fault Injection

To mimic low frequency drift, the selected monitored clock input is purposely divided down by two before being allowed to clock the counter, resulting in lowering the final accumulation value to half the expected figure.

The count value, once captured, is then compared with the contents of the four threshold limit registers to determine its current deviation against the set criteria.

As expected,

  • If BUF[31:0] < LWARN[31:0], LWT interrupt flag is set high with clock warning interrupt output based on the warning threshold limit, active high invoked.
  • If BUF[31:0] < LFAIL[31:0], LFT interrupt flag is also set high with clock failure interrupt output based on fail threshold limit and catastrophic failures invoked.

Low frequency drift Fault injection can be activated by setting FLTINJ[1:0] to 2’b01 at random, subject to LOCK/WREN.

Note:
  1. FLTINJ[1:0] bits are not self-cleared by hardware. They maintain their programmed value until cleared by software to assist the ISR handler with its discovery process.
  2. Detection of this artificial Fault will not occur if the limit tolerances are set too high. The function is for the detection of 50% margin below nominal or tighter.