cu port always busy on Mac

Question

I'm going bonkers here. I'm using a Macbook Pro with Yosemite. Connected to the MKS Gen-2Z V1.1 reprap board (ATmega 2560).

The Arduino IDE only shows the cu port being available and not the tty.

Any attempts at opening the CU port show it as being busy. This is also true when I open the port using PronterFace (3d printer software). Yet, the PronterFace shows the tty port and gladly opens it and communicates. I downloaded Arduino 1.0.6 and the tty is available in the dropdown menu and it will open the port. But my 3D printer firmware will fail building on any Arduino IDEs prior to 1.6.0.

I found a few suggestions on creating a file "lock" in /var/ and then changing the r/w permissions. Also doing the same for /var/spool/uucp. Changing both of those permissions did nothing for me.

I may just have to build it and use AVRdude directly so I can use the tty port, but I have no idea why the cu would be busy all the time. Any suggestions?

Here's the Arduino output when I try to upload:

avrdude: ser_open(): can't open device "/dev/cu.usbserial-AL00YS9R": Resource busy
ioctl("TIOCMGET"): Inappropriate ioctl for device
ioctl("TIOCMGET"): Inappropriate ioctl for device
avrdude: ser_send(): write error: Bad file descriptor
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

Answer 1

Can't you see what's hooking the serial port with sudo lsof -n | grep cuaU0 ? If so, sudo kill -9 12345, where 12345 is the offending PID. Your FTDI chip may need a driver, try sudo dmesg after pluggibg it in, or use systemprofiler.

Answer 2

JRobert - I'll have to try the csrutil suggestion. The problem I see with that is the board I am trying to interface with has a genuine FTDI chip, the 232RL. The answer posted was to install a driver for a chinese USB chip.

Gerben - I do have a /dev/tty.usbserial-AL00YS9R. The Arduino IDE is only showing the cu ports.