Clock Synchronization Mechanism

# FlexRay Fault-Tolerant Midpoint clock synchronisation algorithm
# Per FlexRay Protocol Specification v3.0.1, Section 5.4

def fault_tolerant_midpoint(offset_measurements, g_min_sync=2):
    """
    offset_measurements: list of (node_id, measured_offset_ns) from sync frames
    Returns: clock correction to apply in NIT
    """
    if len(offset_measurements) < g_min_sync:
        return 0  # insufficient sync nodes — no correction

    offsets = sorted([m[1] for m in offset_measurements])
    n = len(offsets)

    # Discard highest and lowest (fault tolerance against 1 faulty sync node)
    if n >= 4:
        trimmed = offsets[1:-1]  # remove 1 from each end
    else:
        trimmed = offsets

    # Midpoint = average of trimmed set
    correction = sum(trimmed) / len(trimmed)
    return correction

# Example: 4 sync nodes measured
measurements = [
    ("ECU_A", 50),    # 50 ns offset
    ("ECU_B", 45),    # 45 ns offset (could be faulty outlier)
    ("ECU_C", 200),   # 200 ns offset — suspicious, will be trimmed
    ("ECU_D", 48),    # 48 ns
]

correction = fault_tolerant_midpoint(measurements)
print(f"Clock correction: {correction:.1f} ns")
# With outlier 200 trimmed and 45 trimmed: average of [50, 48] = 49 ns

/* Read FlexRay global time via AUTOSAR StbM (Synchronized Time-Base Manager) */
#include "StbM.h"
#include "FrIf.h"

StbM_TimeStampType  globalTime;
StbM_UserDataType   userData;
Std_ReturnType      retVal;

/* Read FlexRay-derived synchronized time base */
retVal = StbM_GetCurrentTime(STBM_SYNCHRONISED_TIME_BASE_FLEXRAY, &globalTime, &userData);

if (retVal == E_OK) {
    /* globalTime.seconds + nanoseconds = absolute FlexRay cluster time */
    uint32_t cycle_number = FrIf_GetCycleCounter(FR_CHANNEL_A);
    uint16_t macrotick    = FrIf_GetMacrotick(FR_CHANNEL_A);
    /* Use for timestamping safety-critical events with µs-level accuracy */
}