Arduino flasher 3.3v

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This explains how to:

  • Easily lower the voltage of an arduino
  • Use that arduino to flash a coreboot image on a GM45 Thinkpad with a SOIC16 chip

It requires:

  • An AVR Arduino at 5v
  • An USB<->Serial adapter capable of providing enough current to power up:
    • The arduino
    • The flash chip
    • The circuits around the flash chip

It was tested with:

  • An "nano version 3.3"
  • A Sparkfun "FTDI Basic 3v3" (Uses an FTDI FT232R)


  • It requires not to ever connect an USB cable between the Arduino USB port and the computer while the flasher is connected to a flash chip. This would result in the I/O voltage being 5V instead of 3.3V. If you think you may accidentally connect it this way, this flasher isn't the right solution for you.
  • For now it requires to patch frser-duino


In the Atmega328/P datasheet, the "32.3. Speed Grades" chapter describes (pages 368 and 369) the link between maximum frequency of the microcontroller and the voltage. At 3.3v, the maximum frequency is 12Mhz.


Build the code and flash it

Building frser-duino

First download frser-duino:

$ git clone --recursive
$ cd frser-duino

Then modify the F_CPU value in main.h to be 12Mhz instead of 16Mhz: F_CPU will look like that:

#define F_CPU 16000000UL

Change it to:

#define F_CPU 12000000UL
  • Flash the Arduino with frser-duino
$ make ftdi

Flashing the arduino

Before flashing the arduino we want to make sure that we are talking to the right device. To do that make sure that the arduino is not connected to your computer and run:

$ ls -l /dev/ttyUSB0 

If everything went fine it will output something like that:

ls: cannot access '/dev/ttyUSB0': No such file or directory

If instead it looks like that:

crw-rw---- 1 root uucp 188, 0 27 févr. 14:30 /dev/ttyUSB0

then something else is connected to your computer at /dev/ttyUSB0. If you can't figure what's going on by yourself, it's better to get help on the flashrom IRC channel to fix the issue.

Then connect your arduino to the computer and run the same command:

$ ls -l /dev/ttyUSB0 

This time it's supposed to output a line that looks more or less like that

crw-rw---- 1 root uucp 188, 0 27 févr. 14:30 /dev/ttyUSB0

At this point we're pretty confident that /dev/ttyUSB0 corresponds to the arduino, so we can flash it with:

$ make flash-ftdi

Once it is flashed we can now test that everything went fine with:

$ flashrom -p serprog:dev=/dev/ttyUSB0:2000000

This will make flashrom talk to the arduino to verify if everything is fine up to this point.

If everything went fine it will look more or less like that:

$ flashrom -p serprog:dev=/dev/ttyUSB0:2000000
/sys/firmware/dmi/tables/smbios_entry_point: Permission denied
/dev/mem: Permission denied
/sys/firmware/dmi/tables/smbios_entry_point: Permission denied
/dev/mem: Permission denied
flashrom v1.0 on Linux 4.15.2-gnu-1 (i686)
flashrom is free software, get the source code at

Using clock_gettime for delay loops (clk_id: 1, resolution: 1ns).
serprog: Programmer name is "frser-duino"
serprog: requested mapping AT45CS1282 is incompatible: 0x1080000 bytes at 0xfef80000.
No EEPROM/flash device found.
Note: flashrom can never write if the flash chip isn't found automatically.

This is the important line:

serprog: Programmer name is "frser-duino"

It means that flashrom is able to talk to the flasher, which reports itself as "frser-duino" We also have the following line:

No EEPROM/flash device found.

which tells that it didn't find any flash. This is what's supposed to happen since we didn't connect any yet.

Build the programmer

Connect the programmer to the USB<->Serial adapter

To do that:

  • Connect the FTDI adapter to RX and TX of the arduino
  • Connect the 3V3 of the FTDI adapter to the 5V pin of the Arduino
  • Connect the GND of the FTDI adapter to the GDN of the arduino.

Here's a sumarry of the above:

Arduino USB<->Serial port adapter
5v 3.3v
  • You can now check that the programmer is responding with:
flashrom -p serprog:dev=/dev/ttyUSB0:2000000

Since you didn't connect yet a flash chip, it will says it found no flash chips:


  • If you use a clip (Like a SOIC-8 or SOIC16 Pomona clip), connect it to the arduino
  • Connect the chip to the clip, or if you don't use a clip, the chip to the arduino
Arduino pin number Function Flash chip function SOIC8 Flash chip pin SOIC16 Flash chip pin
  • Connect an USB cable between the USB<->Serial adapter and the computer. Never connect the cable between the Arduino USB port and the computer while the flasher is connected to a flash chip. That would result in the I/O voltage being 5V instead of 3.3V.


Run flashrom like that:

flashrom -p serprog:dev=/dev/ttyUSB0:2000000

With some strange macronix flash chip (that are present in the Thinkpad X200) you might need to add spispeed=100k like that:

flashrom -p serprog:dev=/dev/ttyUSB0:2000000,spispeed=100k


Thanks a lot to SwiftGeek on IRC (#libreboot on Freenode) for finding the first workaround to make it detect flash chips at lower voltage. This project would not have been possible without that.

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