using UNO R4 Wifi with IDE2.3.4 in Windows 11. I can upload my blinky sketch just fine from the IDE. When I try to run the following line from the command line, tho, I get "No device found on COM3". Even tho the arduino IDE uses COM 3 also. Here is the line and error:
C:\Windows\System32>"C:\Users\RobertOujesky\AppData\Local\Arduino15\packages\arduino\tools\bossac\1.9.1-arduino5/bossac" -d --port=COM3 -U -e -w "C:\Users\RobertOujesky\AppData\Local\arduino\sketches\9144B9EB1CD4BF9BEC21C2EBE1773425/AP1.ino.bin" -R
No device found on COM3
Here is the output window from the arduino IDE
Performing 1200-bps touch reset on serial port COM3
"C:\Users\RobertOujesky\AppData\Local\Arduino15\packages\arduino\tools\bossac\1.9.1-arduino5/bossac" -d --port=COM3 -U -e -w "C:\Users\RobertOujesky\AppData\Local\arduino\sketches\9144B9EB1CD4BF9BEC21C2EBE1773425/AP1.ino.bin" -R
Set binary mode
version()=Arduino Bootloader (SAM-BA extended) 2.0 [Arduino:IKXYZ]
Hi @roujesky. The UNO R4 WiFi must be put into a special mode before it can accept an upload via bossac. As @sterretje mentioned, Arduino IDE automatically puts the board into this mode before running the bossac command. It does this by momentarily opening the serial port of the UNO R4 WiFi board at 1200 baud (this is referred to as the "1200 bps touch).
There is code in the "Arduino UNO R4 Boards" core that runs in the background of your sketch program and recognizes this "1200 bps touch" as a special signal that the board should be put into the boot mode.
There is an alternative method for putting the board into that mode. You do it by pressing the "RESET" button on the board twice quickly. After you do that, you will see the "L" LED on the board start pulsing to indicate it is in the boot mode.
Do that and then try running the bossac command again. Hopefully it will be successful this time.