On Sun, Jul 28, 2019 at 07:37:26PM -0500, hal wrote:
> On 7/28/19 3:57 PM, hal wrote:
> <snip>
> >
> > Some searching says to add "core_freq=250" or "enable_uart=1" but
> > so far still nothing. Any suggestions are appreciated.
>
> I got the serial port working. It's a bit of a task. Apparently the
> bluetooth integration messed up the serial port configuration so
> when you boot, you're actually connected to the bluetooth chip
> on /dev/ttyAMA0. You have to fiddle with /boot/config.txt and
> /boot/cmdline.txt to restore the serial functionality.

Nice to hear that you got it working! As you mention, I remind that
there was something :-) Some time ago, I was going to use the
serial port with an LTE shield. I remind I also had to fiddle
with it to get it working.

Actually, RPi 3 B+ has two UARTs. The usual/default UART is
connected with Bluetooth chip by default, thus the Pins on the
header are not working - as you already found out.

If you want to use Bluetooth and UART: There is another UART
in RPi 3 B+ which can be mapped to Bluetooth instead.

you could be using
core_freq=250
dtoverlay=pi3-miniuart-bt
instead of
dtoverlay=pi3-disable-bt

This additional uart does not support full speed / handshake but fast enough
for bluetooth in any case. I think it only works with fixed clock freq.

cheers,
Andreas