Topic: Kernel change for faster USB serial?

Osman Eralp of the HomeBrew Robotics Club and I are working on a balancing robot that has gyroscope reading coming in over an FTDI USB serial link.  The problem is that the reading come in every four milliseconds but the select loop returns every 16 milliseconds having accumulated four readings.  We need to get the reading on the 4 ms edges when they come in.   We have already changed the kernel tick rate from 100 HZ to 1 KHz and this change seems to work fine.  The same application code works fine on a PC so we know it is something in the Chumby.

What kernel config parameter sets how long the USB subsystem will hold onto data before posting it via a select() call?


Re: Kernel change for faster USB serial?

is the /sys entry to control the latency of the FTDI serial driver.  Setting this from its default value of 16 to  2 solved the problem.

Bob Smith

Re: Kernel change for faster USB serial?

Cool trick, thanks!