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Get the firmware

You can either take a pre-built firmware package from or build your own firmware. If you take the prebuilt package, extract it to a directory of your choice.

Three different storage areas

Every microcontroller has three parts that can be flashed (written):

  • Three fuse bytes contains microcontroller specific configuration bits. These should only be set once.
  • The flash memory contains the firmware. It can be overwritten about 10.000 times.
  • The EEPROM memory contains (firmware) configuration data. It is also written to by the device in normal operation. It can we overwritten about 100.000 times.

In general, it's a good idea to only flash what you need to, because of the limited amount of possible write cycles.

Programming fuses

Using a make rule

If you build your binaries by yourself with “make”, your fuse settings should be available as files lfuse.bin, hfuse.bin and efuse.bin in the bin subdirectory of the device you want to flash. You can write these fuses with:

make program_fuses

Be sure about the fuse settings you want to write in your microcontroller. With wrong fuse settings, your microcontroller might not be accessible anymore!

Calling avrdude directly

If you are creating a new or modified SHC device, you may want to write other than the default fuses. You can do so with:

avrdude -p ATMEGA328P -U lfuse:w:0x??:m

(replace ?? by the hex value for the needed fuse settings and use “lfuse”, “hfuse” or “efuse” accordingly).

Strange avrdude error messages

Some fuses only use a part of their bits. If you set such a fuse, avrdude may complain at verification that it read out another value than it wrote.

Writing the EFuse of the ATMega168 or 328 returns a value of only the last 3 bits (upper 5 unused), so a value of xxxxxyyy is read out as 00000yyy. Example:

avrdude: verification error, first mismatch at byte 0x0000
         0xfc != 0x04
avrdude: verification error; content mismatch

Don't worry. The warning is only returned because avrdude does not know that the upper 5 bits are always 1 (as per spec).

Flashing the firmware / eeprom

Using flash scripts

After setting up avrdude, you can flash the firmware by calling the flash scripts

  • flash.cmd / for flashing firmware, eeprom and fuses
  • flash_firmware.cmd / for flashing only the firmware

Using a make rule

If you have the source code on your machine, you can flash the firmware with the following command from the firmware subdirectory:

make program

Calling avrdude directly

If you want to call avrdude by hand you can flash everything with:

avrdude -p m328p -U flash:w:shc_basestation.hex -U eeprom:w:shc_basestation.e2p:r -U lfuse:w:lfuse.bin:r -U hfuse:w:hfuse.bin:r -U efuse:w:efuse.bin:r

(leave one part “-U …” out to flash only a part).

flash_the_atmega.txt · Last modified: 2023/03/01 19:40 by breaker27