Decoding Simulink's UDP Packets in Python?

Question

I have a Simulink model sending data via UDP to another program (Blender) where I can receive the packets, but I have not been able to figure out how to correctly decode them. In the Simulink model I just have it sending a value that is based upon a sine wave, nothing fancy, just a single value like 1.452 or something. In Blender I have it spitting out the data it receives from the packet, and I'm receiving stuff like: b'<\\xa6ya\\x05\\x93\\xe3?' I have no idea how to decode this. It seems to have some hex values, but beyond that I'm lost. I'm not even sure what all this data contains. Is it just the value from Simulink, or does it contain information regarding things like the sender and receiver IP addresses, ports, etc...? **UPDATE**: I updated the Simulink model to transmit a constant value via UDP for debugging/investigation. The value is 0.5234, and the data that my Python script is spitting out is: b'\\xab>W[\\xb1\\xbf\\xe0?' Which, when converted into hexadecimal reads (using hexlify): b'ab3e575bb1bfe03f' How would I extract/decode 0.5234 out of that? Thanks for any help!

Answer 1

The value b'ab3e575bb1bfe03f' is a hex representation of the number in float 64 but it is stored in little endian format. https://www.geeksforgeeks.org/little-and-big-endian-mystery/

If you plug 0.5234 into this calculator http://weitz.de/ieee/ (make sure that binary64 is selected at the bottom) you get: 0x3FE0BFB15B573EAB which is the big endian representation of the number.

Incidentally the previous value that you got before you used hexlify

b'\\xab>W[\\xb1\\xbf\\xe0?'

is converted to hex by recognizing that the \\ character represent escape characters in ascii decoding.

\\x means the next byte (2 character) are hex but the rest of the string is ascil http://www.asciitable.com/

So the string can be interpreted as

. hex ascii ascii ascii hex hex hex ascii

b' \\xab > W [ \\xb1 \\xbf \\xe0 ? '

x' AB 3E 57 5B B1 BF E0 3F

Hope this helps.