Adding a GPS Module (hat/shield) on a Raspberry Pi

[Shamim Shahriar]

Good morning all

I had been searching for a solution for the last 3 days, and tried 
various different things based on the google results, but so far no 
luck. Hope someone from the list can shed some light and maybe point me 
to the correct direction.

Here is the scenario:

Device: Raspberry Pi B (pi 1 model b, the 512M RAM version, or more 
precisely v1.2)
GPS Module : Ublox hat that sits perfectly on the Pi, with PPS on GPIO-18
FreeBSD version: 11.1 RELEASE for RPI-B

As I understand, the serial ports on the GPIO is activated by default, 
and if I attach "ONLY" a serial console (USB to serial), I can interact 
with the Pi through the console. Remove serial console cable, attach the 
Pi to a display (via HDMI), boot it up -- it works just fine.

If now I add the GPS module/hat/shield, all I get is series of dots 
(depending on how soon the GPS finds the satellites and starts sending 
the data) and the Pi does not boot at all.

Based on
https://forums.freebsd.org/threads/59485/
https://lists.freebsd.org/pipermail/freebsd-arm/2017-March/015845.html
https://vzaigrin.wordpress.com/2014/12/13/liberation-of-the-serial-console-in-the-freebsd-on-the-raspberry-pi/

I have managed to get to the point where I can see that if I have only 
the serial console cable attached, it stops interacting with the boot 
process after a while (the boot continues, and I can see that on the 
HDMI output). But that also stops interacting with whatever signal is 
being sent via that console).

And if I attach the GPS module now, it refuses to boot and drops me to a 
loader> prompt

My understanding (and I might be very very wrong) is, the u-Boot system 
is now being affected and hence cannot boot.

I am not new to FreeBSD, had been using it since the 4.4BSD Lite days, 
but I am seriously baffled by how difficult (nearly impossible) it had 
been to get rid of the serial console (something so easy and taken for 
granted on the i386 or other similar architecture). One of the links I 
found 
(https://www.cryptomonkeys.com/2014/01/freebsd-raspberry-pi-gps-ntp/) 
even suggested that I need to create custom image to get PPS working. 
Well, working PPS comes *after* being able to boot the device with the 
GPS hat/module/shield on -- and I am still stuck at that level.

Any help/pointer/suggestion/direction in this respect is greatly 
appreciated.

Best regards