60.6.3.3.9.3 Tuning Dynamic Detection
The signature refresh rate (signature clock) and the sensitivity of the detection can be tuned in the Dynamic Signatures Tuning register (SECUMOD_DYSTUNE). The tuning is common to all signatures, but each pair has its own independent detection mechanism.
For each pair, once enabled, the detection mechanism increments an error counter after each mismatching pattern detected on the receiver pin. Concurrently, consecutive matching patterns increment another counter. When this counter reaches the threshold programmed in SECUMOD_DYSTUNE.RX_OK_CORREL_NUMBER, the error counter is reset. When the error counter reaches the threshold programmed in SECUMOD_DYSTUNE.RX_ERROR_THRESHOLD, an alarm is generated. The overlapped behavior of these two counters results in the ability of the system to tolerate a pattern error ratio below which no alarm is generated. This ratio derives from the programmed fields though the following formula:
Tolerated Error Ratio = (RX_ERROR_THRESHOLD -1) / RX_OK_CORREL_NUMBER
A great flexibility is given in the programming interface to let the user find the best setting for the application.
The detection algorithm state machine is illustrated in the figure Dynamic Detection Mechanism State Machine. The terms used are as follows:
- Error counter = NBERR
- Consecutive matching patterns counter = PATTERN_OK
- RX_OK_CORREL_NUMBER field = OK_THR
- RX_ERROR_THRESHOLD field = ERR_THR
Various scenarios of state machine operation are illustrated in the figures Dynamic Signature Ongoing, No Error, Dynamic Signature Ongoing, One Error, Dynamic Signatures: Resetting Error Counter After Receiving a Sufficient Number of Good Patterns and Dynamic Signatures: Raising Alarm After Receiving a Sufficient Number of Bad Patterns.