wfjm.w11/tools/sys

This directory contains udev rule files which ensure that

• FTDI based USB UARTs are operated with low latency
• Digilent FT2232C style FPGA boards receive a persistent device name

Each Digilent FT2232C style FPGA board has a unique serial number of the USB interface. This can be used to assign a human readable alias of the form /dev/fpga_... to a board. The file 92-retro-usb-persistent.rules contains example rules valid for the boards of the author. This file must be adopted to the available boards before it is used. Use

    udevadm info -q all -n /dev/ttyUSB1
    #
    # /dev/ttyUSB1 is correct if the FPGA board is the only USB tty device.
    # If you have other USB tty devices adopt to your needs
    #

to determine the ID_SERIAL_SHORT and create rules for your boards.

To set up udev rules do

    cd $RETROBASE/tools/sys
    # !! adopt 92-retro-usb-persistent.rules to your needs !!
    sudo cp -a 91-retro-usb-latency.rules    /etc/udev/rules.d/
    sudo cp -a 92-retro-usb-persistent.rules /etc/udev/rules.d/
    sudo chown root:root /etc/udev/rules.d/*-retro-usb-*.rules
    ls -al /etc/udev/rules.d/

    sudo udevadm control --reload-rules

to verify whether usb device has low latency use

    # --> deterime the /dev/ttyUSB* device of interest
    cat /sys/bus/usb-serial/devices/ttyUSB1/latency_timer
    # --> should show '1' and not '16'

and to verify whether persistent device name are applied use

   ls -al /dev/fpga_*
   # output like
   #  lrwxrwxrwx 1 root root 7 2020-03-15 13:55 /dev/fpga_arty -> ttyUSB1