Unsigned CRC32 check

Using Arduino Programming Questions
#1

Hi all!

been dealing for a couple of days with this and I’m pretty much stuck. Wrote a simple function on a Python script to interact with an electronic device, this device uses a CRC32 check as part of its serial communication protocol. My current Python function looks like this:

def calculate_crc(payload):
   crc = binascii.crc32(binascii.unhexlify(str(payload)))
   return hex(crc % (1<<32))

So for a desired payload I got the CRC32:

>>> calculate_crc('620004')
'0xb37f0245'

Which is OK as I tested against the device. Now, porting the code to Arduino, I hit a wall when trying to replicate this same behavior.

I’ve tried to use:

Without any luck, no matter what I do, I cannot replicate the same CRC32 I got from the Python script. Aside from that I receive different values, which leads me to think I’m not handling it very well.

The implementation hardware guide says:

CRC32: This is the big-endian 32 bit CRC or all payload bytes i.e. excluding size and CRC. The CRC32 is
implemented as per public domain ‘crc32.c’ (http://www.csbruce.com/software/crc32.c)

Can anyone help me point the right direction?

Thanks in advance

#2

What about porting the code at the website you linked?

EDIT:
What Arduino board are you using? I do see that the static table in that code would take up half of the available RAM on an Uno.

#3

Hi!
Porting the code was one of my ideas, but I'm not such a good programmer so I think I'll mess up all the code before getting it working :stuck_out_tongue:

I'm using an Arduino UNO, and yes, that static table is quite big for the UNO maybe.

What I think I'm missing here is the unhexlify from Python, which converts the 620004 HEX to BIN, then crc32 calculates its crc32.

#4

masterl1nk:
Porting the code was one of my ideas, but I’m not such a good programmer so I think I’ll mess up all the code before getting it working :stuck_out_tongue:

Seems like a good learning opportunity. Get started on it and post here when you get stuck.

#5