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  • It appear the new UNOs use the optiboot bootloader. Optiboot check if the reset button is pressed (or reset it pulled low via the DTR signal), and if not, will runs your sketch immediately (removing the 3 second delay). So I don't think these pieces of code will work. Commented Jul 31, 2020 at 12:43
  • @Gerben, Uno always used Optiboot. version 4 as bundled with the core package Commented Jul 31, 2020 at 12:45
  • Thank you for the reply. ((FLASHEND-512)>>1) gives 16127, which is 0x3EFF. The bootloader starts in the next flash word (0x3F00), so I don't think jumping to 0x3EFF will work. And, as I said, I already tried jumping to 0x3F00. :/ Commented Aug 1, 2020 at 1:46
  • @Nuno, sorry. jumping to 0x3F00 with Optiboot 8 will work. github.com/Optiboot/optiboot/blob/… Commented Aug 2, 2020 at 8:49
  • @Juraj I see, if I change the bootloader to Optiboot 8 it may work. Thanks! I'll give it a try when I have some free time. I'm not sure if the bootloade can replace itself, so it'll take a little more effort as the arduino pins for SPI flashing are currently inaccessible. Commented Aug 3, 2020 at 2:13