Cubieboard does not boot when UART is connected

[max0ne]

I am trying to use a Cubieboard 2 to communicate to a PIC32 micro controller through UART. 

The Cubieboard is running a Lubuntu os installed onto flash memory.

I disabled the auto-serial-console process at /etc/init/auto-serial-console so that the system does not interfaces with my UART communication, and once that is done I can successfully use the UART channel at /dev/ttyS0 and everything works fine.

However the Cubieboard does not boot to the operating system when I have the UART connected ( have Cubieboard's RX connected to micro controller's TX, Cubieboard's TX connected to micro controller's RX, ground connected together, micro controller powered up ), it gets stuck here:

It boots and operates fine if I connect the devices together after the Cubieboard is finished booting.

Here is how they are connected:

Both devices' UART voltages are 3.3v.

I am guessing the Cubieboard enters a development mode that listens to commands from UART if it finds the UART channel is connected? But I have no idea how to disable this.

Any suggestions?

Thanks

[Kenta]

2014年4月19日土曜日 2時47分30秒 UTC+9 max0ne:

when I used Cubieboard2 installed Cubian,

I had  same issue.

Cubian uses u-boot  for booting. It listens commands by serial console from /dev/ttyS0. Getting any command, u-boot don't boot kernel　but enters u-boot's setting mode.

I could't disabled u-boot listening commands from /dev/ttyS0 in u-boot's setting mode.

Instead of /dev/ttyS0, /dev/ttyS1 and other pins can be used.

[Henrik Nordström]

fre 2014-04-18 klockan 10:47 -0700 skrev max0ne:
> I am guessing the Cubieboard enters a development mode that listens
> to commands from UART if it finds the UART channel is connected? But
> I have no idea how to disable this.

It is the u-boot bootloader. It stops at some input to allow you to
boot another kernel etc. In many ways similar to grub or ntldr on your
PC.

You can disable this in the u-boot settings. See bootdelay setting
<url:http://www.denx.de/wiki/view/DULG/UBootEnvVariables>

Doing these settings is most easily done if you have a serial terminal
allowing you to interact with u-boot. If you don't have this then it
gets a little tricker.

This do not disable messages from being printed on the console port
during the boot process however. If you need the port to be completely
silent then it's likely better to pick another UART port on the
Cubieboard for your device instead of the system console port. Should
be two or three UARTs available on the expansion pins, but some
configuration may be needed to enable them.

Regards
Henrik