Booting Raspberry Pi with input on serial console

[Ian Lepore]

On Fri, 2017-03-10 at 11:40 +0100, Peter Ankerstål wrote:
> Hi!
> 
> I have a problem that should (?) have a simple solution but I havent
> found one. 
> 
> I have a raspberry pi with a NMEA-GPS constantly hooked up to the
> serial console of the Pi. 
> 
> My problem is that when booting the Pi it will interpet the output
> from the GPS as input to the boot process and the boot will fail. How
> can I have the serial interface of the GPS permanently hooked up to
> the pi without preventing the system to boot?
> 
> Thanks!
> 
> /Peter.

Ideally, the fix for this would be to "setenv stdin nulldev; saveenv",
but unfortunately our copy of uboot is missing the option to include
nulldev in uboot.

I think a viable workaround for your case is probably to create a
uEnv.txt file on the fat partition of the sdcard and put in it:

 bootdelay=0
 stderr=lcd
 stdout=lcd

That will prevent uboot from stopping if the gps receiver sends some
text, and prevent uboot from sending most of its text output to the
serial port, which may confuse the gps receiver (the uboot startup
banner text still appears on the serial port tho).

-- Ian