Raspberry Pi I2C Support

[Todd Kolmodin]

Hello all,

I searched for this topic but did not see anything specific regarding the I2C Bus.  I have Pi-3s that run stacked TNC-Pi TNCs from Coastal Chipworks. However I can only run APRX on one of the TNCs as it is running on the serial bus.  To run stacked TNC-Pis you have to run them on the I2C bus.  So right now I cannot run two transmitters on the PI with APRX as I don't see we have support for the I2C bus as of yet.  If I am missing the answer  posted somewhere else, please send me in that direction with my sincere apologies. 

73, Todd N7TRY

SHERWD APRS Digipeater

Sherwood OR (APRX39)

[Jason Buchanan]

hi - 

I have a TNC-Pi - works great.

You have to configure the TNC-Pi to use I2C and you can only do this with one TNC-Pi connected to the Raspberry Pi.  

Here's what I used to move from serial to I2C:

./pitnc_getparams 0 0       # view parameters

./pitnc_setparams 0 0 7 16  # set tnc-pi to address 16 (10 hex)

./pitnc_setparams 0 0 15 2  # reboot tnc-pi

# board should now be readable on i2c bus at address 16 /dev/i2c-1

./pitnc_getparams 1 16

# I pull the power cord from the Rasbperry Pi to fully test the configuration

poweroff

Adjust TXDelay and other values as needed:

./pitnc_setparams 1 16 1 32 # TXDelay 32 - this is radio-specific

./pitnc_getparams 1 16      # view parameters

Hope this helps.

73 Jason N1SU

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[Jason Buchanan]

forgot to mention - each TNC-Pi needs to be on a unique address - you can't put them all on address 16.

Take a look at http://tarpn.net/t/builder/builders_configure_tnc_pi.html - more details there.

[Jason Buchanan]

... and after you configure each board to be on a unique address you can stack them all back together - it's only when moving them from serial to I2C that you have to have only one board connected.  After they each have a unique address you can reconnect them all back in a stack.

[Todd Kolmodin]

Thanks Jason. I am familiar with switching the TNC-Pi between Serial and I2C.  I'm just trying to find out the syntax that would be used

in the aprx.conf for the interfaces.  If I set my two Pis to I2C Bus 1, Devices 16 and 17, how to I call them correctly in aprx interfaces?

73, Todd

On Wed, Jul 3, 2019 at 9:20 PM Jason Buchanan <jason.b...@gmail.com> wrote:

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[Jason Buchanan]

Got it - I use ax25.

$ cat /etc/ax25/axports 

# /etc/ax25/axports

#

# The format of this file is:

#

# name callsign speed paclen window description

#

1 N1SU-3 19200 255 2 TNCX

A snippet of my /etc/aprx.conf:

mycall  N1SU-3

. . .

 <interface>

     ax25-device  $mycall

     tx-ok        true

     telem-to-is  true

 </interface>

 <digipeater>

     transmitter    $mycall

     <source>

         source         $mycall

         relay-type     digipeated

         viscous-delay  5

         ratelimit      60 120

     </source>

     <source>

         source         APRSIS

         relay-type     third-party

         viscous-delay  5

         msg-path WIDE2-2 # gate TX with 2 hops for messages

         via-path WIDE1-1 # gate TX with 1 hop for everything else

     </source>

 </digipeater>

I have some regex-filters and other stuff but these are the highlights.  I use msg-path to help propagate messages for delivery - it improves the "quality of life" for message senders/receivers.

This is what I use to start the interface and aprs as a systemd service:

$ cat aprx_start 

axup=$(ifconfig -a | grep flags | awk -Fflags '{print $1}' | grep ax0)

if [[ -z $axup ]];

 then

  echo "ax0 does not exist - attempting to create it"

  /usr/local/bin/i2ckiss 1 16 1 10.1.1.1

 fi

mkdir -p /var/log/aprx

sudo /usr/sbin/aprx -i

I did a lot of tweaking to reduce writes to the SD card - /var/log is a small 50M mount against tmpfs and I create the log directory for use across reboots.

The start script is used to create the ax0 interface used by aprx.

thanks,

Jason

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