Connect the Arduino Uno to the Arduino Pro Mini as shown below and don't forget to add the 10 ♟ to 100 ♟ capacitor between the reset pin and ground on the Uno.Go to File->Examples->ArduinoISP and flash that sketch to the Arduino. Disconnect everything from the Arduino Uno.There are lots of tutorials online on how to connect an Arduino Uno as ISP. You can buy a cheap one online or use another Arduino. To flash a new bootloader an ISP or In-System-Programmer is needed. Sudo git apply ~/patch.diff Flashing optiboot using another Arduino as ISP cd /usr/share/arduino/hardware/arduino/avr/ You need to restart the Arduino IDE for the changes to take effect. The above patch can be applied with the following commands. +pro.file=optiboot/optiboot_atmega328.hex pro.file=atmega/ATmegaBOOT_168_atmega328.hex Only the path to the bootloader file and the upload speed have to be changed: diff -git a/boards.txt b/boards.txt On Arch Linux the file boards.txt is located in the following directory: /usr/share/arduino/hardware/arduino/avr/boards.txt It is already used for the Arduino Uno boards, so we just have to copy the settings from there. In the meantime you can just patch the file boards.txt to point to the optiboot bootloader. Patching boards.txtĪt the time of writing it is not possible to add optiboot using the Board manager of the Arduino IDE, but it seems that there is work on the way to make this possible in the near future. The obvious solution is to flash optiboot on the Arduino Pro Mini, which is exactly what I did. It turns out, that the Arduino Uno, which doesn't have the issue, by default comes with optiboot as its bootloader, but the Arduino Pro Mini, which uses exactly the same chip, does not. Replacing the Arduino Pro Mini Bootloader The Arduino is stuck in its bootloader and the function void setup() is never executed. Apparently this doesn't happen on the Arduino Pro Mini and the Watchdog times out before the bootloader finishes, which leads to another reset. So the very first thing the bootloader should do is deactivate the Watchdog. The Source of the ProblemĪfter a reset that was initiated by the Watchdog timer, the Watchdog is still active and the timeout period is automatically set to a very short time. The sketch works as intended on the Arduino Uno which uses exactly the same chip. You have to physically disconnect the power to recover the Arduino Pro Mini. You cannot upload a new sketch and the reset button doesn't work. If the bootloader is in this infinite loop, nothing works anymore. Instead it blinks for one second, waits for 8 seconds and then sends the bootloader into an infinite reset loop. So it should blink for a second, go into the infinite loop for 8 seconds, until the Watchdog automatically resets the sketch, and blink again for one second. The call to wdt_enable(WDTO_8S) sets the Watchdog timer to 8 seconds. The statement while(1) creates an infinite loop to simulate a crash. The following simple sketch illustrates the problem. The microcontroller can crash or enter an infinite loop for any number of reasons, so an automatic recovery from these states is an important feature. The Watchdog timer is used to reset the microcontroller, if it is non-reactive for a certain period of time. I have just spent several hours debugging a very annoying issue with the Arduino Pro Minis Watchdog timer, until I finally realized that the fault wasn't in my code, but in the bootloader. How to make the Watchdog timer work on an Arduino Pro Mini by replacing the bootloader Author Andreas Rohner Date Sun Category Electronics How to make the Watchdog timer work on an Arduino Pro Mini by replacing the bootloader My Notebook
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