MicroPython Forum

kevinkk525

Good arguments. Now I'm a bit unsure. Maybe I'll make it configureable :D Let the user decide.. recipe for disaster? :D I guess it could make sense to secure the whole package with a proper crc even if it slows the code down by 4-8ms. Thanks for the crc16 code! When I use that code at 400Bytes it ta...

kevinkk525

Thank you! I'm a bit wary of adding more overhead with an even bigger/more crc since the communication is already slow enough due to processing time. I have a few checks in place: First a START_BYTE is read, then a 6 byte header including the crc8 is being read, which also contains the length of the...

kevinkk525

oh well.. then I would need a crc16 for up to 500Bytes? ... I just want some fast way to recognize garbae on my uart. Shouldn't crc8 be enough for that? Or is it recommended to use crc16?

kevinkk525

This is not the same code as above and you return "width" which is not in the class. You need to return "self.width" as in your first post.

kevinkk525

yeah the message is 4bit vs 8bit but if it takes longer, it won't help the transmission speed. Sending an additional byte takes 80us so it's faster to just send more.

kevinkk525

Thanks a lot! Interestingly this crc4 algorithm needs twice the time of my crc8 lookup table algorithm

On a 400Byte bytearray crc8 takes 2.5ms, this crc4 takes 6ms.

kevinkk525

How do I get to crc4 from this:

Code: Select all

def crc8(*args, initial_value=0):
    _sum = initial_value
    table = _table
    for arg in args:
        for byte in arg:
            _sum = table[_sum ^ byte]
    return _sum

Since you created a script for the tables, you probably have an example code too?

kevinkk525

Yeah I was more busy than I expected :D Yes in many applications the performance might not be too important. In general I'd say the current state will add 50-100ms to communication. Haven't tested it with mqtt_as yet because in the current state there is one major problem: With non-blocking sockets ...

kevinkk525

I do have a working minimal codebase now between 2 esp32 over uart but I'm wondering about the performance. I might have overdone the protocol and the processing time for optimizations takes longer than just sending the frames without optimizations :lol: It was a premature decision coming from ardun...

kevinkk525

Thanks, generated a new table with this! looks good.

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