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c4f33e1c9d
- 99-retro-usb-permissions.rules renamed to 90-retro-usb-permissions.rules
- 91-retro-usb-latency.rules: udev rule to enforce low latency for FDTI USB UART
- 92-retro-usb-persistent.rules: udev rule for persistent device names
- Note:
- for all FTDI USB-UART it is essential to set them to `low latency` mode.
That was default for linux kernels 2.6.32 to 4.4.52. Since about March
2017 one gets kernels with 16 ms default latency again, thanks to
kernel patch 9589541. For newer systems it is essential to install the
udev rule which automatically sets low latency.
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
To setup udev rules do
# !! 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'