Re: Raspberry Pi 3?

"John Wiseman" <john.wiseman@...>


I think you’ve missed my point. The Pi3 now has /dev/ttyS0 where
/dev/ttyAMS0 used to be without adding any overlays. But by default its

speed will vary with the GPU clock, and will start out about 40% slower. You
can get get round this by throttling the GPU or by disabling Bluetooth and
putting /dev/ttyAMS0 back where it was.

But as far as I can see, you can’t have the serial port, full performance
and Bluetooth. You’ll have to choose which to sacrifice.


Sent: 09 March 2016 22:01
Subject: Re: [UniversalDigitalRadio] Raspberry Pi 3?


On Mar 6, 2016, at 10:32 AM, 'John Wiseman'
[UniversalDigitalRadio] <> wrote:

There have been some significant changes to the serial port (ttyAMA0 is
now used for Bluetooth, and the new ttyS0’s speed depends on the GPU clock),
so probably not without some work.

I just got a chance to check this out today after clearing some other stuff
from my plate. I don’t yet have an RPi 3 (They should arrive on Friday and
I’ll give another report based on that), but you can access the Mini-UART on
the RPi 2 by using a device tree overlay. Add:


to your /boot/config.txt and you’ll end up with a /dev/ttyS0 that are on the
same pins as /dev/ttyAMA0. Pins BCM14 and BCM15 have both UARTs available on

I did this and hooked up a PiDV to the RPI 2 and ran AMBEserver -i
/dev/ttyS0. I then used Buster to listen to a reflector. No audio dropouts
and everything seems to work fine.

The issues I’ve been seeing around using the Mini-UART are all surrounding
using it as a console, not as a peripheral after boot-time. There are issues
with the clocks being gated correctly and such. The firmware does some
initial setup, and if you’re not careful you can gate the wrong clocks and
really mess up the system. We’re watching the clock code rather closely
because we are using one of the general purpose clocks on the RPi in the
soon-to-be-released UDRC.

But the upshot of this all is that the PiDV should work okay on the RPi 3. I
will post a definitive answer when I get a RPi 3 for testing.


John G8BPQ


Jeremy McDermond (NH6Z)
Xenotropic Systems

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