ATmega328P-PU 12MHz bootloader

It took me an embarrassingly long time to get a 328 with a 12MHz crystal working so that it would allow a normal (serial / FTDI) upload from the Arduino IDE.

There are a few older guides around but I didn’t find one that used the newer optiboot bootloader.

If you don’t want to compile the bootloader yourself, you can download the compiled optiboot_at328mega_12.hex file from this link (right-click and and Save (link) as…) just copy it to your optiboot folder before editing your “boards.txt” file as described below.

If you want to compile the hex file yourself here’s how:

Edit the Makefile in your optiboot folder. On my (Windows 7 64bit) machine using Arduino 1.0.5-r2 this folder was C:\Program Files (x86)\Arduino\hardware\arduino\bootloaders\optiboot

Add this section. I put it in after the existing atmega328 sections and before the Sanguino section  (note that the -W1, … shouldn’t be on a separate line – it’s a continuation of the LDSECTIONS line, but this blogging software seems to want to wrap it onto a new line):

atmega328_12: TARGET = atmega328
atmega328_12: MCU_TARGET = atmega328p
atmega328_12: CFLAGS += '-DLED_START_FLASHES=3' '-DBAUD_RATE=115200'
atmega328_12: AVR_FREQ = 12000000L
atmega328_12: LDSECTIONS  = -Wl,--section-start=.text=0x7e00 -Wl,--section-start=.version=0x7ffe
atmega328_12: $(PROGRAM)_atmega328_12.hex
atmega328_12: $(PROGRAM)_atmega328_12.lst

atmega328_12_isp: atmega328
atmega328_12_isp: TARGET = atmega328
atmega328_12_isp: MCU_TARGET = atmega328p
# 512 byte boot, SPIEN
atmega328_12_isp: HFUSE = DE
# Low power xtal (12MHz) 16KCK/14CK+65ms
atmega328_12_isp: LFUSE = FF
# 2.7V brownout
atmega328_12_isp: EFUSE = 05
atmega328_12_isp: isp

This is just a copy of the atmega328. section with:

  • the name changed from atmega328. to atmega328_12.
  • the f_cpu parameter changed from 16000000L to 12000000L
  • the two (PROGRAM) lines changed so that the .hex and .lst filenames also have the “_12” addition
  • the comment about the 16MHz crystal frequency changed to 12MHz

Run a command shell as administrator and navigate to the optiboot folder.  Enter the following command to compile the new 12MHz optiboot bootloader:

omake atmega328_12

Now edit your boards.txt file.  On my machine this was located at C:\Program Files (x86)\Arduino\hardware\arduino  Add this new section at the end – again this is just a copy of the ‘uno’ section with the few obvious edits for frequency and bootloader file.

##############################################################

atmega328bb12.name=ATmega328 12MHz crystal
atmega328bb12.upload.protocol=arduino
atmega328bb12.upload.maximum_size=32256
atmega328bb12.upload.speed=115200
atmega328bb12.bootloader.low_fuses=0xff
atmega328bb12.bootloader.high_fuses=0xde
atmega328bb12.bootloader.extended_fuses=0x05
atmega328bb12.bootloader.path=optiboot
atmega328bb12.bootloader.file=optiboot_atmega328_12.hex
atmega328bb12.bootloader.unlock_bits=0x3F
atmega328bb12.bootloader.lock_bits=0x0F
atmega328bb12.build.mcu=atmega328p
atmega328bb12.build.f_cpu=12000000L
atmega328bb12.build.core=arduino
atmega328bb12.build.variant=standard

Now launch Arduino, select “ATmega328 12MHz crystal” as your board and “Burn Bootloader” from the Tools menu.

That’s it, and you should be up and running with the normal hardware serial port working correctly with the ‘Serial’ commands and serial uploading from the Arduino IDE also working correctly.  I’ve seen comments that not all of the timing functions (microsecond delays etc.) work accurately when using a 12MHz crystal and the standard Arduino libraries.  I’ve not investigated that yet; and so far I’ve not tried using software serial with a 12MHz crystal – that also may require some tweaking…

 

 

4 thoughts on “ATmega328P-PU 12MHz bootloader”

  1. For the chineese version of Arduino Uno, many people using default uno, so they brick board. Thank you for your instruction, But newest version of Arduino Ide, board.txt should be like this :

    atmega328bb12.name=ATmega328 12MHz crystal
    atmega328bb12.upload.protocol=arduino
    atmega328bb12.upload.maximum_size=32256
    atmega328bb12.upload.speed=115200
    atmega328bb12.bootloader.low_fuses=0xff
    atmega328bb12.bootloader.high_fuses=0xde
    atmega328bb12.bootloader.extended_fuses=0x05
    atmega328bb12.bootloader.file=optiboot/optiboot_atmega328_12.hex
    atmega328bb12.bootloader.unlock_bits=0x3F
    atmega328bb12.bootloader.lock_bits=0x0F
    atmega328bb12.build.mcu=atmega328p
    atmega328bb12.build.f_cpu=12000000L
    atmega328bb12.build.core=arduino
    atmega328bb12.build.variant=standard
    atmega328bb12.bootloader.tool=arduino:avrdude
    atmega328bb12.upload.tool=arduino:avrdude

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