Does anybody know a website that explains the neccessary steps for uploading a Bootloader program to an AVR?
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Just to "upload" is no different to ISP/JTAG programming any other "normal" code into an AVR. It's just the .hex (or .elf) file involved will have code based at a high address rather than just 0x0000.
While doing ISP (etc) you will probably have to change some fuses too. Almost certainly BOOTRST (activate it) but you might have to adjust BOOTSZ fuses too depending on the starting point of the bootloader code.
There's a fair amount on the Optiboot github wiki page: https://github.com/Optiboot/opti...
(Yes, it's written to be about Optiboot specifically, but a lot of it should be useful as general information.)
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