3 Replies Latest reply on Mar 29, 2021 7:09 AM by misaz

    Raspberry Pi OS FTDI channel Cap / limit?

    daemoninformatica

      I'm currently experimenting with a setup where I install a lite version of Raspberry Pi OS on a Pi 4 (8GB version).

      Installation (using NOOBS) and configuration for ssh was painless and so was installing some python3 libraries and utilities.

       

      The problem I run into is the following: Using 2 4-port hubs, I'm trying to connect several (currently 5) FTDI cables. I wrote a simple python script to read the serial input and if any input was there, pass it on over mqtt to a server (in local network. )

      The thing is, this appears to work for 4 channels (FTDI cables) but as I add a second hub with the 5th channel, serial data goes 'missing'. (isn't passed on properly). Each channel has its own identical but separate python serial to mqtt process.

      The processor and memory are basically idleing, so I can't imagine there should be a limit there.

      In recent past, I've tried this setup with a Pi 3, and ran into the same problem. Figuring it had to do with the very limited bridge between CPU and USB / network, I upgraded to the Pi 4 that should have a different architecture (solving the limit)

      But even so: These serial connections aren't passing actually a lot of data (we're talking KB's per minute.)

       

      I was wondering: could there be some cap / limit on serial / USB interfaces in the software (kernel)? During these 'missing data' periods, the device doesn't actually disconnect (or show any other error) according to dmesg.