Alan Cox alan@lxorguk.ukuu.org.uk writes:
On Wed, 29 Sep 2010 11:55:21 -0400 "Roger K. Wells" ROGER.K.WELLS@saic.com wrote:
I have a RS485 serial device (Quatech SSU2-300) that when plugged into a USB (2.0) port appears to be recognized correctly. dmesg yields:
cp210x 3-1:1.0: cp210x converter detected usb 3-1: reset full speed USB device using uhci_hcd and address 8 usb 3-1: cp210x converter now attached to ttyUSB0
A "C" language program attempting to use this port hangs at the open call.
This same program with the same device worked on a Centos 5.5 install on the same computer.
uname -r : 2.6.34.7-56.fc13.x86_64
The USB device works in Windows XP so I don't think there is a defect there.
Modern kernels properly handle carrier detect and wait so open it with O_NDELAY if you don't want to wait for the carrier line to be asserted and/or set the CLOCAL termios bits if you are not using the carrier and flow control.
One of my pet peeves is people that wire up 3-wire rs-232 (ground, tx, rx) and then wonder why they can't open the port. Carrier detect is a very useful line for detecting if the rs-232 plug fell out of the computer. People should get in the habit of at least looping RTS->CTS, DTR->{DSR,DCD}.
-wolfgang