The Problem and Fix
How to use a usb/serial adapter



THE PROBLEM AND FIX

I was having the following problem with the pl2303 usb serial
driver. (For example, I have been using it with an model GUC232A
USB/Serial adapter to connect to a SV203 servo controller board.
  http://iogear.com/main.php?loc=product&product_id=154
  http://www.pontech.com/products/sv200/)

The serial driver would throw away the CR/LF after the first
line and then freeze. This problem is also documented on the
RedHat site: 
  http://www.redhat.com/archives/redhat-list/2004-February/msg01052.html

I got the driver to work by adding a 1 msec delay at the end of the
pl2303_write function. (500 usec didn't work.) I don't know why this
worked and will probably not investigate. 1 ms is a long time. 
USB sends out a frame of packets every ms.

The folks at Ohio State have been using this driver and I 
don't know why it was working for them before this fix. So keep
the original pl2303.o around in case the new one doesn't work
in your environment.



HOW TO USE A USB/SERIAL ADAPTER

* Copy the new pl2303.o into
      /lib/modules/2.4.19.../kernel/drivers/usb/serial

* Load the USB serial modules by executing the USB serial startup script
      /etc/rc2.d/K94loadserial

* Plug in the USB/serial adapter

* To test send a string to a serial device
      cat > /dev/usb/tts/0