Re: BeagleBone Black doesn't boot without serial console (10.0 release)

[Brook Milligan <brook%nmsu.edu@localhost>]

> On Oct 11, 2024, at 9:33 AM, Dr. Nicola Mingotti <nmingotti%gmail.com@localhost> wrote:
> 
> Indeed, disconnecting the serial cable creates troubles to the kernel,
> see here, video i made before reading this message.

In the video it looks like you have a live BBB and then pull off the serial cable.  That absolutely will not work as it changes the levels on the Rx line in particular, which is what the kernel is listening to.  If you can, look at this with an oscilloscope or possibly a voltmeter.

The 10k pull-up resistor I mentioned will prevent the line level changes and the kernel will be happy, even if you connect/disconnect the serial cable from a live BBB.  I added the resistor to solve exactly this problem and it works fine.

> I changed already BBB, powering method (POE , battery), power input plug
> (micro USB / barrel jack), the problem is
> independent from all of those.

This is entirely about the line level change on the serial Rx that occurs when the cable is removed.  Power source, etc. will have no effect.

> I will see, probably better i conclude this project with a RPi3B+ where
> i accumulated already more experience in NetBSD,
> i also found other surprises about GPIO with BBB, i will say in another
> message.

I am using the BBB GPIO pins to controll a bunch of stuff and for input.  They work perfectly well.

By default, different pins have different properties with respect to pull-up/pull-down/input/output/etc.  You need to know what is the nature of the pins you are using to be sure they match the purpose.

Somewhere I have them all mapped out, but you can figure that out pretty easily if you have a 100k resistor and a voltmeter.  For any given pin, place the resistor between the pin and ground, then measure the pin voltage with the BBB powered on.  Repeat for the resistor between the pin and 3.3v.  From the voltages, you can determine if there are internal pull-up/pull-down resistors enabled; from the known resistor you can also determine the value of the internal resistors.  Confirmin input/output is also easy; just enable the pin, read/set it with gpioctl, and see if the voltage corresponds to what you expect.

I don’t expect you really need to switch hardware for these reasons.

Cheers,
Brook