SEGGER RTT Console
==================

Objective
---------

Sometimes you dont have UART on your board, or you want to use it for
something else while still having newt logs/shell capability. With
`SEGGER's RTT <https://www.segger.com/jlink-rtt.html>`__ capability you
can swap UART for RTT, which is a very high-speed memory-mapped I/O.

.. contents::
  :local:
  :depth: 2

Hardware needed
~~~~~~~~~~~~~~~

You'll need a SEGGER J-Link programmer in order to use this advanced
functionality. You might have an external J-Link programmer you're
already using, or maybe your board has a dedicated J-Link onboard as
some development kits do. Another possibilty is J-Link OB firmware
available for some devices like the micro:bit.

Setup the target
~~~~~~~~~~~~~~~~

We'll assume you have an existing project with some kind of
console/shell like :doc:`Blinky with console and shell <../blinky/blinky_console>`
that we're switching over to RTT from UART.

**Note:** We have tested RTT with J-Link version V6.14h. We recommend
that you upgrade your J-Link if you have an earlier version of J-Link
installed. Earlier versions of J-Link use the BUFFER\_SIZE\_DOWN value
defined in hw/drivers/rtt/include/rtt/SEGGER\_RTT\_Conf.h for the
maximum number of input characters. If an input line exceeds the
BUFFER\_SIZE\_DOWN number of characters, RTT ignores the extra
characters. The default value is 16 characters. For example, this limit
causes shell commands with more than 16 characters of input to fail. You
may set the Mynewt ``RTT_BUFFER_SIZE_DOWN`` syscfg setting in your
target to increase this value if you do not upgrade your J-Link version.

We can disable uart and enable rtt with the newt target command:

.. code-block:: console

    newt target amend nrf52_blinky syscfg=CONSOLE_UART=0
    newt target amend nrf52_blinky syscfg=CONSOLE_RTT=1

Run the target executables
~~~~~~~~~~~~~~~~~~~~~~~~~~

Now 'run' the newt target as you'll need an active debugger process to
attach to:

.. code-block:: console

    $ newt run nrf52_blinky 0
    App image succesfully generated: ~/Downloads/myapp1/bin/targets/nrf52_blinky/app/apps/blinky/blinky.img
    Loading app image into slot 1
    [~Downloads/myapp1/repos/apache-mynewt-core/hw/bsp/nrf52-thingy/nrf52-thingy_debug.sh ~/Downloads/myapp1/repos/apache-mynewt-core/hw/bsp/nrf52-thingy ~/Downloads/myapp1/bin/targets/nrf52_blinky/app/apps/blinky/blinky]
    Debugging ~/Downloads/myapp1/bin/targets/nrf52_blinky/app/apps/blinky/blinky.elf
    GNU gdb (GNU Tools for ARM Embedded Processors) 7.8.0.20150604-cvs
    Copyright (C) 2014 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
    and "show warranty" for details.
    This GDB was configured as "--host=x86_64-apple-darwin10 --target=arm-none-eabi".
    Type "show configuration" for configuration details.
    For bug reporting instructions, please see:
    <http://www.gnu.org/software/gdb/bugs/>.
    Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.
    For help, type "help".
    Type "apropos word" to search for commands related to "word"...
    Reading symbols from ~/Downloads/myapp1/bin/targets/nrf52_blinky/app/apps/blinky/blinky.elf...done.
    0x000000d8 in ?? ()
    Resetting target
    0x000000dc in ?? ()
    (gdb) 

Connect to console
~~~~~~~~~~~~~~~~~~

In a seperate terminal window ``telnet localhost 19021`` and when you
continue your gdb session you should see your output. If you're not
familiar with telnet, when you're ready to exit you may by using the
hotkey ctrl+] then typing quit

.. code-block:: console

    $ telnet localhost 19021
    Trying ::1...
    telnet: connect to address ::1: Connection refused
    Trying fe80::1...
    telnet: connect to address fe80::1: Connection refused
    Trying 127.0.0.1...
    Connected to localhost.
    Escape character is '^]'.
    SEGGER J-Link V6.14e - Real time terminal output
    SEGGER J-Link EDU V8.0, SN=268006294
    Process: JLinkGDBServer

Then you can interact with the device:

.. code-block:: console

    stat
    stat
    000262 Must specify a statistic name to dump, possible names are:
    000262  stat
    000262 compat>