Fix timestamp offset bug in BLFWriter

[pierreluctg]

In the BLF files, the frame timestamp are stored as a delta from the "start time". The "start time" stored in the file is the first frame timestamp rounded to 3 decimals. When we calculate the timestamp delta for each frame, we were previously calculating it using the non-rounded "start time".

This new code, use the "start time" as the first frame timestamp truncated to 3 decimals.

This code can be used to test if the written timestamps are the same that we read back from the BLF file.

import time

import can

messages = [
    can.Message(arbitration_id=_, is_fd=True, is_extended_id=False, timestamp=time.time() + _) for _ in range(10)
]


def main():
    can_log_files = [
        "logfile1.blf",
    ]

    for file_name in [None] + can_log_files:
        with can.Logger(file_name) as logger:
            for message in messages:
                logger(message)

    for file_name in can_log_files:
        print("Reading", file_name)
        with can.LogReader(file_name) as reader:
            for message in reader:
                print(message)

    for timestamp_delta in [1.0e-3, 1.0e-4, 1.0e-6]:
        print(f"timestamp_delta={timestamp_delta}")
        for file_name in can_log_files:
            with can.LogReader(file_name) as reader:
                for i, message in enumerate(reader):
                    assert message.equals(messages[i], timestamp_delta=timestamp_delta, check_channel=False), (
                    messages[i], message)
        print("OK")


if __name__ == "__main__":
    main()

[zariiii9003]

That makes sense. Maybe add a code comment, so this does not get "optimized" away in the future.

[pierreluctg]

That makes sense. Maybe add a code comment, so this does not get "optimized" away in the future.

I have also updated/fix the unit tests test data to avoid hitting this issue in the future.