Using ARM Cortex-M Single Wire Output (SWO)

About this document

This document describes how to use Cortex-M SWO to output data from .NET nanoFramework.

Prerequisites

You'll need:

• Target board with SWO pin free and configured in it's reset state (meaning not used by GPIO or any other peripheral and not configured in any alternate mode).
• If using a stock board it's also convenient to check the schematics if any hardware changes are required.
  • STM F429I_DISCOVERY board requires solder bridge SB9 to be soldered
  • STM F769I-DISCO board requires a 0 Ohm resistor on R92 (or just soldering the pads toghether)
• Software capable of driving and outputting data from an SWO source. (ST-Link)[http://www.st.com/content/st_com/en/products/embedded-software/development-tool-software/stsw-link004.html] is an excellent tool for this purpose.
• Set .NET nanoFramework build options to include support for SWO (either setting "SWO_OUTPUT" : "ON" in cmake-variants.json or launching CMake with -DSWO_OUPUT=ON).

Outputting SWO

1. Load the target flash with a .NET nanoFramework image build with SWO option

2. On ST-Link menu choose ST-Link -> Printf via SWO viewer

1. After SWO viewer windows loads, set the Sytem clock to match the target and the Stimulus port to 0.

1. Click the Start button and watch the output in the main window area.