error: first mismatch at byte 0x7800

Of course you know that the FLASH memory is limited, but in some cases you want to use it up to the last byte that is 0x8000 minus the bootloader.

The bad news is: there are different kinds of bootloaders taking either 2 kBytes or 0.5 kBytes. But nowadays we are used to find the smaller one, called "Optiboot". In rare cases there might be the old one installed, and you will miss some 1500 bytes.

To find out which bootloader is installed you might use the sketch fusebytes.

It will need access to a file called "avr_cpunames.h" which you will find on your harddisk. You probably have to move it to a directory where is will be found by gcc.

If it tells you your Arduino has the 2048 bootloader installed don't hesitate to install the new one. There are many ways to do this.

contact: nji(at)