fixed latency issue with serial port

[astumpf]

This patch fixes the communication timeouts due to increased latency settings in newer Ubuntu kernels. The patch is based on http://projectgus.com/2011/10/notes-on-ftdi-latency-with-arduino/.

[astumpf]

For some reason the programmatic solution does not work on every system. Although the latency timer was set to 1 which can be verified with

cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

it does not influence the system behvoir at all.

However,

echo 1 | sudo tee /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

seems to work always so far. Does anyone know why?

[LeonJung]

@astumpf

Hallo, Alex,
wie gehts es dir

since I'll be in IROS next week,
My handling for this issue will be started from Octover 20th, I guess

entschuldige and I hope that you have patience on it

[astumpf]

Adding udev rule
ACTION=="add", SUBSYSTEM=="usb-serial", DRIVER=="ftdi_sio", ATTR{latency_timer}="1"
works perfectly for now. However, programatic solution is preferred.

[LeonJung]

@astumpf

Hi,
what you said was perfect. I put some description for latency timer settings in the code comments.

[astumpf]

Awesome und vielen Dank!