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.
- 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)
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.
Open the Preference
dialog of the Arduino IDE and paste the following two Board Manager URLs
into the list:
https://felias-fogg.github.io/ATTinyCore/package_drazzy.com_ATTinyCore_plus_Debug_index.json
https://felias-fogg.github.io/MiniCore/package_MCUdude_MiniCore_plus_Debug_index.json
Close the Preference
dialog with OK
. Now, we want to install the two cores, ATTinyCore
and MiniCore
.
- Select
Tools
->Board
->Board Managers
... . This will open the Boards Manager dialog. - In the search field, type
MiniCore
and install the most recent version (or upgrade to the most recent one), which has a+debug-2.X
suffix. - Afterward, do the same with
ATTinyCore
.
Check: Select Tools
-> Board
-> ATtinyCore
-> Attiny25/45/85 (no bootloader)
. Then check whether there is an entry Debug Compile Flags: "No Debug"
when you click on Tools
again. Check that also for Tools
-> Board
-> MiniCore
-> Atmega328
.
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
ortar.gz
, - download it to your hard disk,
- extract the firmware from the downloaded archive using
unzip
ortar -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
underTools
as the destinationboard
, - select the right
Port
in theTools
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
.
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 a UNO as a target board is described in Section 4.5.2 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.
ATtiny pin# | Arduino UNO pin | component |
---|---|---|
1 (Reset) | D8 | 10k resistor to Vcc |
2 (D3) | ||
3 (D4) | 220 Ω resistor to target (red) LED (+) | |
4 (GND) | GND | red and yellow LED (-), decoupling cap 100 nF, RESET blocking cap of 10µF (-) |
5 (D0, MOSI) | D11 | |
6 (D1, MISO) | D12 | |
7 (D2, SCK) | D13 | |
8 (Vcc) | D9 | 10k resistor, decoupling cap 100 nF |
RESET | RESET blocking cap of 10 µF (+) | |
D7 | 220 Ω to system (yellow) LED (+) |
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:
- not connected (LED is off),
- waiting for power-cycling the target (LED flashes every second for 0.1 sec)
- target is connected (LED is on),
- ISP programming (LED is blinking slowly),
- error state, i.e., not possible to connect to target or internal error (LED blinks furiously every 0.1 sec).
Note that state 2 (power-cycling) will be skipped in our configuration, where the debugger provides the power supply to the target via a GPIO line and does the power-cycling for you.
Check: Go through the table above and check every connection. Wrong wiring can often cause hours of useless software debugging!
- Load the sketch you want to debug (e.g.,
dw-link-x.y.z/examples/varblink/varblink.ino
) into the IDE by choosingOpen...
in theFile
menu. - Select
ATtiny25/45/85 (no bootloader)
as the board underTools
->Board
->ATTinyCore
. - In the
Tools
menu, choose1 MHz (internal)
as theClock Source
(assuming that the ATtiny is as it comes from the factory and no fuse has been changed). - In the
Sketch
menu, selectOptimize for Debugging
. - Compile the code by clicking on 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 thegdb-server
console in the bottom right part of the window. - After the debugger and debug-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, 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.
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 can be that an MCU might not be responsive anymore 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. While a regular exit of the debugger restores the RESET line, the debugger may be terminated without restoring it. An easy cure is to enter the debugger again and leave it regularly (after connecting to the target chip) with the command quit
. 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.
So, what do you do with your newly built hardware debugger after everything has been debugged? 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.