Reading data from Simulink into Python over UDP?

Question

I want to send data from a Simulink model (running in real time) to a Python script (also running in real time. I am using Simulink's built-in "UDP Send" block, which works, but I don't know how to decode the data I'm getting. This is what my python script looks like: import sys, struct from socket import * SIZE = 1024 # packet size hostName = gethostbyname('0.0.0.0') mySocket = socket( AF_INET, SOCK_DGRAM ) mySocket.bind((hostName,5002)) repeat = True while repeat: (data,addr) = mySocket.recvfrom(SIZE) data = struct.unpack('d',data) print data I've suspected that the data stream should be something like a double, but while it's giving me numbers they aren't meaningful: - If simulink sends a constant "1", I get an output of "3.16e-322" - If Simulink sends a constant "2", I get an output of "3.038e-319" Any ideas?

Answer 1

You're using Simulink's UDP Send block to send a constant (like 1 or 2), and in Python you're using struct.unpack('d', data) — but you're getting weird tiny numbers.

Simulink is likely not packing the data correctly as a double (64-bit float). You're decoding 8 bytes, but those 8 bytes are garbage without proper packing on the Simulink side.

Fix:

In Simulink:

1. Use Data Type Conversion to double

2. Use Byte Pack block:

*Set data type to double

*Set output to uint8

3. Send packed output to UDP Send

In Python:

Make sure you're unpacking exactly 8 bytes:

value = struct.unpack('<d', data[:8])[0] # '<d' = little-endian double