When a robostix is plugged in and no tweener is used and no serial
adapter is plugged into the gumstix jack, then you need to put a 10k
resistor between 4 of the gumstix adapter and +5 from one of the UARTs
pins. Some people have also had success putting the resistor beteen
pins 3 & 4 of the gumstix connector.
Failing to install the resistor will cause the boot to think that the
user is causing a Break and it will drop into u-boot.
By default, the robostix is held in reset when booting. You can
perform the modifications mentioned on this page to get the robostix
to run as the gumstix is booting:
I thought you only needed to add the resistor if you had a pre J-fab robostix? I received mine about a month ago, so I assumed it was J-fab. I am looking at this page:
Also, I have already performed the modifications to run the robostix when the gumstix boots. Everything seemed to function when I was using a tweener.