Quick-start Guide for Debugging with the Arduino IDE 2

You can turn your Arduino UNO into a hardware debugger that can be used for embedded debugging of classic AVR chips under Arduino IDE 2. Takes less than one hour.

If you want to debug your classic AVR chips without using Arduino IDE 2, consult the alternative quickstart guide for AVR-GDB debugging.

What you need

• Computer running Windows, macOS, or Linux (the host)

• Arduino UNO (will become the hardware debugger)

• USB cable

• ATtiny85 (or any other classic ATtiny or ATmegaX8) as the target

• In order to connect the hardware debugger to the target, you need either:

  • the dw-link probe shield and an ISP cable, or

  • a breadboard together with

    • 11 Jumper wires (male-to-male)

    • 2 LEDs

    • 3 Resistors (10 kΩ, 220Ω, 220Ω)

    • 2 Capacitors (100 nF, 10 µF)

Step 1: Install Arduino IDE 2

You probably already have installed the Arduino IDE 2. If not, download and install it from https://arduino.cc.

Check: Start IDE and check the About Arduino entry under the Arduino or Help menu for the version number. It should be >= 2.3.0.

Step 2: Install new board manager files

Open the Preferences dialog of the Arduino IDE and paste the following Board Manager URLs into the list:

xxxxxxxxxx
https://felias-fogg.github.io/ATTinyCore/package_drazzy.com_ATTinyCore_index.json
https://felias-fogg.github.io/MiniCore/package_MCUdude_MiniCore_index.json
https://felias-fogg.github.io/MicroCore/package_MCUdude_MicroCore_index.json

Close the Preference dialog with OK. Now, we want to install the three cores, ATTinyCore , MiniCore, and MicroCore.

• Select Tools -> Board -> Board Managers ... . This will open the Boards Manager dialog.

• In the search field, type ATTinyCore and install the most recent version.

• Afterward, do the same with MiniCore and MicroCore.

Check: Select Tools -> Board -> ATtinyCore -> Attiny25/45/85 (no bootloader) . The debug button in the upper row (3rd from the left) is no longer greyed out. Check that also for Tools -> Board -> MiniCore -> Atmega328.

Step 3: Install dw-link firmware on an UNO

Download the dw-link firmware. This means you should

• open the webpage https://github.com/felias-fogg/dw-link,

• click on Latest in the field Releases (on the left),

• choose either zip or tar.gz,

• download it to your hard disk,

• extract the firmware from the downloaded archive using unzip or tar -xvzf.

In order to install the firmware,

• first make sure that the auto-reset feature of the UNO is not disabled, e.g., by a shield or a capacitor plugged into the UNO board,

• then connect the Arduino UNO to your computer with a USB cable,

• open the Arduino IDE and select Arduino UNO under Tools as the destination board,

• select the right Port in the Tools menu,

• and load the dw-link sketch into the IDE, which is located at dw-link-x.y.z/dw-link/dw-link.ino.

• Finally, compile and download the sketch to the UNO by either pressing the right arrow button, or by typing CTRL-U or ⌘U. The UNO acts now as a hardware debugger (but needs a bit of additional hardware).

Check: Open the Serial Monitor (under Tools menu), choose 115200 baud, type - (minus sign) into the upper line, and send it. The hardware debugger should respond with $#00.

Step 4: Hardware setup

This description is for debugging an ATtiny85. However, almost any other classic ATtiny or ATmegaX8 would do. Just be aware that when trying to debug an Arduino UNO board, you need to alter the board physically (cut a solder bridge). How to set up an UNO as a target board is described in Section 4.2.2 of the dw-link manual.

When you are the proud owner of a dw-link probe, and you have a development board for the ATtiny with an ISP connector, the setup is as easy as plugging in an ISP cable, as shown below.

If not, you need to set up the hardware on a breadboard and use six wires to connect the ATtiny to your UNO turned hardware debugger.

Note that the notch or dot on the ATtiny is oriented towards the left.

Here is a table of all connections to check that you have made all the connections.

The yellow LED is the system LED, and the red one is the ATtiny-LED. The system LED gives you information about the internal state of the debugger:

1. debugWIRE mode disabled (LED is off),

2. waiting for power-cycling the target (LED flashes every second for 0.1 sec)

3. debugWIRE mode enabled (LED is on),

4. ISP programming (LED is blinking slowly),

5. error state, i.e., not possible to connect to target or internal error (LED blinks furiously every 0.1 sec).

Check: Go through the table above and check every connection. Wrong wiring can often cause hours of useless software debugging!

Step 5: Start Debugging

• Load the sketch you want to debug (e.g., dw-link-x.y.z/examples/varblink/varblink.ino) into the IDE by choosing Open... in the File menu.

• Select ATtiny25/45/85 (no bootloader) as the board under Tools -> Board -> ATTinyCore.

• In the Tools menu, choose 1 MHz (internal) as the Clock Source (assuming that the ATtiny is as it comes from the factory and no fuse has been changed).

• In the Sketch menu, select Optimize for Debugging.

• Compile the code by clicking the Verify button in the upper left corner.

• Open the debug panes by clicking the debug symbol (bug with triangle) in the left sidebar.

• Click the debug symbol in the top row to start debugging. This will start the debugger and the debug server. The activities are logged in the Debug Console and the gdb-server console in the bottom right part of the window.

• You will probably be asked to "power-cycle the target." This means that you need to remove power from the target and then reconnect it, activating the debugWIRE mode.

• After the debugger and gdb-server have been started, the debugger will start executing the program on the target. Execution will stop at the first line of the setup function.

• Now, you are in business and can set breakpoints (clicking left of the line number), continue executing, stop the program asynchronously, inspect and change values, and examine different stack frames. To terminate your debugging session, click the red box in the debug row.

Be aware that after finishing the debug session, the MCU is still in debugWIRE mode! You can change that by typing monitor debugwire disable in the last line of the Debug Console. More information can be found in the dw-link manual.

What can go wrong?

First, you might be unable to start debugging because the debug button is greyed out. This happens for all MCUs that the IDE cannot debug. If you think that this is an error, you might need to install the correct board definition files or choose the Reload Board Data entry in the Tools menu.

Second, the debug-server might terminate early. In this case, you should see an error message in the gdb-server console.

If something does not work as advertised, it is often a simple wiring problem. Other possible sources of errors are installation errors, i.e., that a program is not installed at the right place, does not have the proper permissions, the PATH variable is incorrect, or one has installed the wrong board manager files. When strange error messages appear, it may also indicate that some components have not been installed. Google for the error message! Often, there are hints on how to mitigate the problem. Finally, there is also a troubleshooting section in the dw-link manual, which may be helpful.

The most annoying problem is that an MCU might not be responsive after a debugging session. The reason is that the RESET line, which is used as a communication line during debugging, has not been re-enabled. The command monitor debugwire disable typed into the lasr line of the Debug Console just before terminating the debugger should restore the RESET line functionality. If this does not help, you may have to use a High-Voltage programmer, such as RescueAVR.

If you have found a bug, please post it on issues and fill out the issue form before.

After debugging has finished

So, after everything has been debugged, what do you do with your newly built hardware debugger? You don't have to throw it away. You can also use it as an ISP programmer (STK500 v1). In the Arduino IDE, such a programmer is called Arduino as ISP or Arduino as ISP fast. In the latter case, the upload speed is 115200 instead of 19200.

If you want a more durable hardware debugging solution, the dw-link manual has some suggestions in Section 8, or you can buy the dw-link probe at Tindie. These days, however, the Microchip debugger MPLAP SNAP might be a better deal. You can use it as a drop-in replacement for dw-link, and it is able to do much more!