Error with timestamp when write a blf file with BLFWriter and read with BLFReader

[shach934]

Describe the bug

Write a blf file with a start_timestamp like: 1636485425.999908, then read with BLFReader, the start_timestamp cannot be interpreted and assigned to 0.

To Reproduce

Try to save a blf file with start_timestamp like 1636485425.999908. then read it with BLFReader.
The error is caused by the following(function systemtime_to_timestamp()) :

    t = datetime.datetime.fromtimestamp(timestamp)
    return (
        t.year,
        t.month,
        t.isoweekday() % 7,
        t.day,
        t.hour,
        t.minute,
        t.second,
        int(round(t.microsecond / 1000.0)),
    )¨

1636485425.999908 will become (2021, 11, 2, 9, 20, 17, 5, 1000). The microsecond part becomes 1000.
When read with BLFReader(function: timestamp_to_systemtime()):

t = datetime.datetime(
            systemtime[0],
            systemtime[1],
            systemtime[3],
            systemtime[4],
            systemtime[5],
            systemtime[6],
            systemtime[7] * 1000,
        )

An error with the microsecond part: systemtime[7] * 1000 is 1000000 over a valid range 0-99999. The start_timestamp will be 0. Information lost.

Suggest: dont round(t.microsecond/1000), instead use: t.microsecond//1000, to keep the first 3 digits.

Expected behavior

Keep the original timestamp.

Additional context

OS and version: Win10
Python version: 3.9.7
python-can version: 4.0.0
python-can interface/s (if applicable):

Traceback and logs

def func():
    return "hello, world!"

[christiansandberg]

Good catch! Would you be able to make a PR?