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

["Dr. Nicola Mingotti" <nmingotti%gmail.com@localhost>]

On Fri-11-Oct-2024 15:58, Brook Milligan wrote:
> > On Oct 11, 2024, at 6:36 AM, Manuel Bouyer <bouyer%antioche.eu.org@localhost> wrote:
> >
> >  From the schematic here:
> > https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fbeagleboard%2FBeagleBone-Black%2Fblob%2Fmaster%2FBBB_SCH.pdf&data=05%7C02%7Cbrook%40biology.nmsu.edu%7C20c9957b85684c02c51408dce9f1823c%7Ca3ec87a89fb84158ba8ff11bace1ebaa%7C1%7C0%7C638642470732586576%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C60000%7C%7C%7C&sdata=IXknH0lQWQWxeS7YvTwVoVFGRoLOaY84J2uZVzkQygc%3D&reserved=0
> >
> > there is a pulldown resitor on UART0_RX input. This means that without
> > a (powered up) USB/serial adapter, UART0_RX sees a logical 0 which
> > is most probably interpreted as a BREAK by the AM335x UART, and causes
> > the kernel to enter DDB.
> >
> > The solution is to either rebuild a kernel without DDB, or tie UART0_RX to
> > a +3.3V pin.
> This agrees with my understanding.  I have had a fair amount of experience with the BBB.  Although I often boot with a serial cable (to be clear: https://ftdichip.com/products/ttl-232r-rpi/), I am sure that I have also done so without and had no problems.  That is, disconnecting the serial cable before powering on the BBB should work fine.
>
> There is, however, a problem with connecting/disconnecting the serial cable on a live BBB; then the signal levels change on the line, which the kernel detects.
>
> I am currently using a 10k pull-up resistor on the Rx line, which allows connection/disconnection of the serial cable on a live BBB without disrupting the kernel.  For example, I can boot the BBB and later connect the serial cable to monitor it without affectiing the kernel.  This works fine for a long-running embedded device.
>
> Cheers,
> Brook


Indeed, disconnecting the serial cable creates troubles to the kernel,
see here, video i made before reading this message.

https://www.dropbox.com/scl/fi/is46koxw4rf95okdney0p/video-hang-bbb.mp4?rlkey=blmueq9qjphw9r7wlbwigfhee&st=usvka65a&dl=0

The quality is xrap but what is going on in is that i connect via serial 
and ssh,
disconnecting the serial broke the ssh connection, the device does not 
answer to ping anymore.

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

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.

bye
Nicola