I was working on a project build initialy from the Arduino IDE to program an attiny84a (without a bootloader) using the board from https://github.com/damellis/attiny

I got an atmel-ice recently and I was trying to debug the arduino sketch using it.

I installed AtmelStudio (because I know it has an GUI debugger) and found VisualMicro that should help me to compile arduino sketch. Unfortunatly as soon as a set the project to debug I got a compilation error :

'Serial' was not declared in this scope

(I don't have this error in Release mode).

My code doesn't use any serial (because I don't have any pin left), so this was wierd. I still tried to add the SoftwareSerial.h include (just in case) without success.

So I created an empty (I mean with only an empty setup() and loop() methods) and it throw the same error.

I tried to setup different versions of arduino IDE into VisualMicro (1.6.13, 1.8.1, 1.8.5 and 1.9 build 34) without success.

Then after a couple of hours I found the .cpp source generated by VisualMicro and it try to use the member "Serial" for some debugging reason.

I would like an easy way to integrate with arduino (all those library and easy to install library) and to be able to debug as well, what can I look for or do?


2 Answers 2


I found how to disable the vMicro debugging, in AtmelStudio open the "vMicro" menu then click the "Debugger" item and make sure the option "Atmel Studio Debugger" is checked.

1) Change the optimization flag to a usefull state (-Og or -O0) in order to NOT have "Unknown identifier" or "Optimized away" when looking at variable.

I tried:

  • Put -Og in the project property "Extra flags" (vMicro)
  • Before my code I added

    #pragma GCC push_options
    #pragma GCC optimize ("Og")

    then at the end of my code

    #pragma GCC pop_option

ANSWER: I probably fuckup in the rebuild because only the line below is enough (in the .cpp file):

    #pragma GCC optimize ("Og") 
  • Replaced -Os in playform.txt (in this case it didn't work at all)

I saw a size changes in my binary (except for the last point), but when running the simulator I still couldn't see any value.

2) Couldn't start a debugging session (When I try to change the debugging device it always crash AtmelStudio, I think it is because the target IC is force to ATSAM3X8E by the vMicro plugin which isn't supported on my computer, and because it isn't supported I can't change the target IC to attiny84a...)

ANSWER: When creating the project vMicro read the current board selected (yes before you even can select it) to detect if it has to create a 32 bits or 8 bits project

Also you MUST create a project with an .ino (even if it is empty) as the same name as the project in order to be able to compile.

'Serial' was not declared in this scope

This error is not surprising when compiling for ATtiny84 because in Arduino Serial refers to the hardware serial port and ATtiny84 doesn't have one.

But you didn't use Serial in your sketch so why should you get this error? The answer is this magical debug feature of Visual Micro that you desire. It turns out that on AVR microcontrollers such as your ATtiny84 all this actually consists of is Visual Micro automatically inserting various Serial.print() statements into your code, just as we always do manually to debug our code in the good old Arduino IDE:


So in fact your sketch is attempting to use Serial without your knowledge or being able to see it! If you turn off debugging you should no longer get that error.

Visual Micro does allow you to change the debugging output to software serial:


but since you say you have no pins available that may not be any help.

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