On Wed, Mar 21, 2012 at 02:47:56PM -0400, Gerald Villemure wrote: > Currently if we want to read the status of the PINs on a serial > port, I need to open the file (e.g. /dev/ttyUSB0) unfortunately in > doing so we *change* RTS/DTR Hm, just opening the port shouldn't change the line settings. Is this unique to the pl2303 driver, or does it also happen on a "normal" serial port as well? > How difficult would it be to extent the usb_serial driver to expose > the pin status like this: > > /sys/class/tty/ttyUSB0/device/RTS (rw, Request To Send) > /sys/class/tty/ttyUSB0/device/CTS (r, Clear To Send) > /sys/class/tty/ttyUSB0/device/DSR (r, Data Set Ready) > /sys/class/tty/ttyUSB0/device/DCD (r, Data Carrier Detect) > /sys/class/tty/ttyUSB0/device/DTR (rw, Data Terminal Ready) > /sys/class/tty/ttyUSB0/device/RI (r, Ring Indicator) > > We could then simply read the file /sys/class/tty/ttyUSB0/device/DCD > and get a 1 if it is high. That would imply that at all times, even if the port is not open, the driver needs to be watching the line settings of the device? For usb to serial devices, this can take a lot of USB traffic to do so, and might make people who care about power usage unhappy. Or we could just do the querying of the device if the sysfs file is open... > We could also control RTS/DTS by using something like: > echo 1 > /sys/class/tty/ttyUSB0/device/DTR > > I realize that if we LIMIT our usage of the serial port to ONLY > serial communication then there is not value is this extension. But > the moment you start using it to drive DIY electronics it would be a > VERY welcomed addition. There is the POSIX interface for serial ports, which we can't ignore, so we need to keep that. But, to extend this to all serial ports, not just USB ones, might be nice for some users. So, care to work on a patch to the tty core that implements this to see if it's even viable? :) greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
