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Nitrogen is a 96Boards compliant IoT Edition board and is a low cost option for debugging Arm Cortex M support in OpenOCD. This guide provides a quick setup guide for Nitrogen board with the outcome of debugging OpenOCD code related to Arm Cortex M support.

Prerequisite: Set up OpenOCD development environment

Host Environment: Ubuntu version 18.04

Build Zephyr Blinky demo for Nitrogen board:

Zephyr getting started guide^[1] provides a step by step guide to set up Zephyr build environment and build a LED blinking demo for Nitrogen board. Following steps are taken from Zephyr getting started guide and more details can be found here^[1].

Install dependencies:

sudo apt install --no-install-recommends git cmake ninja-build gperf

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 ccache dfu-util device-tree-compiler wget

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 python3-dev python3-pip python3-setuptools python3-tk python3-wheel xz-utils file

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 make gcc gcc-multilib g++-multilib libsdl2-dev

Note: Update cmake version if cmake --version returns < 3.13.1

Setup prerequisites and build Zephyr demo app

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Get Zephyr and install Python dependencies:

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install git 
sudo apt install build-essential ncurses-dev doxygen dfu-util device-tree-compiler

Download zephyr from git mirror:

git clone https://gerrit.zephyrproject.org/r/zephyr

Download zephyr-sdk from the link below:

# Install west, and make sure ~/.local/bin is on your PATH environment variable:
pip3 install --user -U west
echo 'export PATH=~/.local/bin:"$PATH"' >> ~/.bashrc
source ~/.bashrc

# Get the Zephyr source code:
west init ~/zephyrproject
cd ~/zephyrproject
west update

# Export a Zephyr CMake package. This allows CMake to automatically load boilerplate code    # required for building Zephyr applications.
west zephyr-export

# Zephyr's scripts/requirements.txt file declares additional Python dependencies. Install them    # with pip3.
pip3 install --user -r ~/zephyrproject/zephyr/scripts/requirements.txt

Install a Toolchain:

# Download the latest SDK installer:
wget https://github.com/zephyrproject-rtos/

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sdk-

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ng/releases/download/

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v0.

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11.

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3/zephyr-sdk-0.

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11.

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3-setup.run

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# Run the installer, installing the SDK in /opt/zephyr-sdk-0.11.3:
chmod +x zephyr-sdk-<version>0.11.3-setup.run
Sudo ./zephyr-sdk-<version>0.11.3-setup.run 

To use the Zephyr SDK, export the following environment variables:

export ZEPHYR_GCC_VARIANT=zephyr
export ZEPHYR_SDK_INSTALL_DIR=<zephyr-sdk-path>/zephyr-sdk/

To use the same toolchain in new sessions in the future create file ~/.zephyrrc

cat <<EOF > ~/.zephyrrc
export ZEPHYR_GCC_VARIANT=zephyr
export ZEPHYR_SDK_INSTALL_DIR=<zephyr-sdk-path>/zephyr-sdk/
EOF

Build Zephyr Hello World sample application

cd <zephyr_root_path>
. zephyr-env.sh
cd samples/hello_world/
make BOARD=96b_nitrogen

Flashing, Running and Debugging using pyOCD

Install Prerequisites:

sudo apt-get install python-pip python-dev python-yaml minicom gdb-arm-none-eabi
sudo -H pip install --upgrade pip
sudo -H pip install --pre -U pyocd

Verify board is detected by pyOCD

sudo pyocd-flashtool -l

Erase the flash memory in the nRF52832

sudo pyocd-flashtool -d debug -t nrf52 -ce

Flash the Hello World application

cd <zephyr_root_path>
sudo pyocd-flashtool -d debug -t nrf52 samples/hello_world/outdir/96b_nitrogen/zephyr.hex

Run minicom to listen for output

sudo minicom -D /dev/ttyACM0 -b 115200

Press reset button on nitrogen board to verify following output

Hello World! arm

Start pyocd-gdbserver in a new terminal window and launch debug session

sudo pyocd-gdbserver
arm-none-eabi-gdb outdir/96b_nitrogen/zephyr.elf
target remote localhost:3333

Flashing, Running and Debugging using openOCD

Build OpenOCD: 

Follow Getting started with OpenOCD Development to build openOCD from sources.

Spawn openOCD connection to Nitrogen Board:

 -d /opt/zephyr-sdk-0.11.3

Build blinky demo and load it up using GDB via OpenOCD:

# Run from the root of the zephyr repository eg: ~/zephyrproject/zephyr
west build -p auto -b 96b_nitrogen samples/basic/blinky

# Connect Nitrogen board to host computer via micro usb cable
# Wait for the MBED folder to mount automatically
# Run OpenOCD from its source folder
./src/openocd -s tcl/ -f interface/cmsis-dap.cfg -c "transport select swd" -f target/nrf52.cf
arm-none-eabi-gdb outdir/96b_nitrogen/zephyr.elf
target remote localhost:3333
target remote localhost:3333

Adding udev rule:

At this point you might be able to use OpenOCD without any issue. However, chances are that you will face with this error message when you try to use OpenOCD on the terminal.

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Assuming that you have your board connected, this is likely to be caused by the current user not having the right access permission to your board USB HID driver. You can verify this by running OpenOCD as root using sudo. However, if we are planning on using OpenOCD with an IDE (for example Eclipse) or some other development environment, then to make our life a little easier we should add a system rule that will automatically mount the our board usb with an open permission so that any user can use it. To do this, we need to first find out our board USB vendor and product id. We can do this by running the USB list command. However, we may need to run this command a few times with and without the board connected to identify which of the USB devices listed belong to our board.

lsusb

You should get a message like this.

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These are two set of hexadecimal characters that you need to make a note of for your device.

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Using this command we are going to create a new udev rule for our USB device. This command will simply create a new text file in the udev rule.d folder which will be invoked when ever out board is connected.

sudo nano /etc/udev/rules.d/CMSIS.rules

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Type in the following lines into the new file. Make sure that you replace the idVendor and idProduct hexadecimal values between the double quotes with the ones that you noted earlier.

KERNEL=="hidraw*", ATTRS{idVendor}=="0d28", ATTRS{idProduct}=="0204", MODE="0666"
SUBSYSTEM=="usb", ATTRS{idVendor}=="0d28", MODE="0666"
SUBSYSTEM=="usb_device", ATTRS{idVendor}=="0d28", MODE="0666"

...

To save the file, press Ctrl+X. Then Press Y and to accept and exit the editor press Enter. You will need to reboot your computer for the new changes to take effect but apart from that you are ready to start using OpenOCD.

To install the latest development version (master branch), do the following:

pip install --pre -U git+https://github.com/mbedmicro/pyOCD.git#egg=pyOCD

Common Errors:

Flashing an Application to 96Boards Nitrogen:

This example uses the Hello World sample with the pyOCD tools. Use the make flash build target to build your Zephyr application, invoke the pyOCD flash tool and program your Zephyr application to flash.

cd <zephyr_root_path>
. zephyr-env.sh
cd samples/hello_world/
make BOARD=96b_nitrogen

References:

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cfg

# Start gdb and load blinky demo onto Nitrogen board's flash memory
/opt/zephyr-sdk-0.11.3/arm-zephyr-eabi/bin/arm-zephyr-eabi-gdb ~/zephyrproject/zephyr/build/zephyr/zephyr.elf -ex 'target remote :3333' -ex 'monitor halt' -ex 'monitor reset' -ex load

Expected output of OpenOCD console after successfully connecting with Nitrogen board

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Expected output of GDB console after successfully loading blinky demo: 

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References:

1. https://docs.zephyrproject.org/latest/getting_started/index.html
2. https://docs.zephyrproject.org/latest/boards/arm/96b_nitrogen/doc/index.html