UART on dev/AMA0 only works when dev/ACM0 is available

[makkes]

Hi !

I have an Atmel ATMega16 connected to the UART header-pins of my RPi-B like this:


To enable UART I altered these files:
/boot/cmdline.txt
/etc/inittab
as seen in many tutorials.
I was following this one:
http://technikegge.blogspot.de/2013/02/ ... asuro.html

And as a matter of fact, this works like a charm as long as I have my ArduinoISP connected to the RPi USB-Port. The ArduinoISP is not connected to my circuit at all, it's only plugged in at the RPi-side.
So to me it looks like plugging in the ArduinoISP (USB) enables something that is needed for the UART.

I am using raspbian,
uname -r returns:
3.12.28+

The ArduinoISP shows as /dev/ACM0, whereas the UART is available as /dev/AMA0.
When I plug off the ArduinoISP, ACM0 disappears, AMA0 is still there, but it's not giving me any output from the AVR.

ArduinoISP:
http://arduino.cc/en/Tutorial/ArduinoISP

Ideas anyone?

makkes

[hansotten]

You have a power supply connected to your Atmega? Or is the ISP powering the Atmega?

[makkes]

Hi,

yes, everything is powered up correctly.

If have absolutely no clue what was wrong, but out of nowhere it suddenly works. I did not change ANYTHING AT ALL. I didn't even reboot the pi.
All I did in the meantime was logging in and out a couple of times via ssh, checking lsmod and lsusb with the Arduino attached/not attached.

makkes

edit:
For sure a setup like this might always have loose connections ...



edit2:
here's the link to the image:
http://postimg.org/image/yod7p93in/[