Serprog/Arduino flasher

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WARNING, make sure that the Arduino SPI voltages and the flash chip voltages matches: Without any extra resistors or level shifter, the Arduino Uno and Duemillanove SPI pins are at 5V, while most chips operate at 3.3v.

Hardware basics

You'll need to have a supported Arduino, which as of writing are any based on the ATmega328 (/168/88 will work with small changes too), like the Arduino Uno R3. Best performance is available with one with an FTDI usb-serial chip (older ones, sparkfun redboard, etc).

And unless the Arduino is a 3.3V version (rare, and the firmware would need small modifications (like MCU frequency) to run on one), you'll also need a way to convert the 5V logic levels to 3.3V, but check that your flash chip is 3.3V and not 1.8V - that would need level conversion in both directions and is not explained here, yet.

And an SPI flash chip that is supported by flashrom.

There will be some simple schematics included here. The idea is that you pick one version from each part 1 through 3, and connect the pin/net names.

Part 1: The Arduino

ATmega328 based ones:

P1v1 arduino328.png

Part 2: Level translation

There are a few options here, ranging from the simple resistors (v1) to a buffer chip (v3).

Here's the simple resistors:

P2v1 resdivider.png

The part count for the resistor divider is 6 resistors of 2 types or 9 of one type.

Here's one with 5 resistors, the downside is that you'll need to modify the firmware a little:

P2v2 oc cs.png

The 3rd version is using the DIP16 HEF4050 buffer chip:

P2v3 buffer4050.png

Part 3: The SPI Flash chip

The smaller DIL-8 and SOIC-8 versions connect like this:

P3v1 dil8 so8 spi.png

Gallery of some flashers

Alternative: Shield with SPI and LPC/FWH for 5V Arduinos

Firmware and hardware sources Shield PCB shared at oshpark

  • This shield and firmware was built for 5V arduinos with FTDI, variations to that will need adaptations in building the shield and/or in the firmware.
  • This shield uses a different pin for SPI CS than the other circuits on this page, and has LPC/FWH capability, thus different firmware.
  • Note: do check for any incompatibilities between your arduino and the shield, eg. the PD7 used as LPC CLK clashes with BT reset in BT arduinos.
  • For LPC/FWH, current (15/03/25) flashrom trunk will not work, until that is fixed use this branch instead.

Compatibility, software and setup


There are some differences between the various arduinos that are relevant for this flasher:


  • Only the AVR architecture is supported for now, because the code depends on avr-libc. In one hand that makes it portable across other non-arduino AVR boards, but it also makes it incompatible with the arduinos that don't have an AVR.

USB<->serial converter

  • Some Arduinos have an FTDI USB<->Serial converter, we can achieve a very high speed of 2000000 bauds with ir.
  • Some Arduino have a 8u2/16u2 instead: This is an extra microcontroller which does the USB<->serial conversion trough a firmware build on LUFA. While that brings lower cost and more flexibility, the downside is that in our case the default firmware was not written for speed over 115200. To get more speed we would need to write another firmware for it.
  • Some Arduinos don't have an USB<->serial converter, like the arduino leonardo. Instead they have a native USB port.
  • Most/All Arduinos have an accessible serial port on their pins. if you have an extra USB<->Serial converter, you can plug it to theses pins. BE SURE TO CHECK THE VOLTAGE COMPATIBILITY BEFORE ATTEMPTING THAT.


  • Some arduinos are at 3.3v.
  • Some are at 5v. Unfortunately most SPI chips are at 3.3v at the time of writing.


Arduinos Hardware User notes
  • Arduino uno
  • Has a 8u2 or 16u2 for the USB<->Serial converter
  • Uses 5V logic levels.
  • Arduino nano
  • Uses 3.3v logic
  • Has an FTDI
  • using the three wires serial and lowering the speed all problems disappear; the code has to be changed to reflects the new speed (115200); to program the board use "avrdude -c arduino -vv -P /dev/ttyUSB* -p atmega328p -b 57600 -U flash:w:serprog.hex"
  • Arduino Duemilanove
  • Has an FTDI
  • Uses 5V logic.
  • Arduino leonardo
  • Lacks an USB<->Serial converter
  • Arduino Leonardo
  • Untested


Required software

To make it work you need:

  • A recent flashrom with the serprog protocol compiled in (most packaged versions do)
  • frser-duino which runs on the arduino
    • This page used to link to serprog-duino, frser-duino should build in a similar fashion and has better serial buffering and some other features (spi speed setting).
  • The avr toolchain(avr-gcc, avr-libc,make etc...)

Building the software

First get the firmware source:

$ git clone --recursive git://
$ cd frser-duino

Then build it:

For a board with a 8u2 or a 16u2:

$ make u2 && make flash-u2

For a board with an ftdi:

$ make ftdi && make flash-ftdi

Running flashrom

The right flashrom arguments are explained in the, or here:

Available targets:
ftdi, flash-ftdi:
  For the Arduinos with an FTDI
  compatible flashrom arguments: flashrom -p serprog:dev=/dev/ttyUSB0:2000000
  Other boards using an hardware USB<->Serial converter might work too.
u2, flash-u2:
  For the Arduino with a 8u2 or a 16u2
  compatible flashrom arguments: flashrom -p serprog:dev=/dev/ttyACM0:115200

So for a board that has an ftdi that would give:

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


The speed is very dependant on the flash chip used:

  • Its capacity impacts the speed a lot, as you would expect.
  • The chip model as also a huge impact.

With the duemillanove:

# time flashrom -p serprog:dev=/dev/ttyUSB0:2000000 -r duemillanove.rom      
flashrom v0.9.7-r1711 on Linux 3.18.3-gnu-1 (i686)
flashrom is free software, get the source code at

Calibrating delay loop... delay loop is unreliable, trying to continue OK.
serprog: Programmer name is "serprog-duino"
Found Winbond flash chip "W25Q32.V" (4096 kB, SPI) on serprog.
Reading flash... done.
flashrom -p serprog:dev=/dev/ttyUSB0:2000000 -r duemillanove.rom

we have:

4.23s user 0.29s system 8% cpu 56.010 total

With the Arduino uno:

# flashrom -p serprog:dev=/dev/ttyACM0:115200 -r uno.rom                
flashrom v0.9.7-r1711 on Linux 3.18.3-gnu-1 (i686)
flashrom is free software, get the source code at

Calibrating delay loop... delay loop is unreliable, trying to continue OK.
serprog: Programmer name is "serprog-duino"
Found Winbond flash chip "W25Q32.V" (4096 kB, SPI) on serprog.
Reading flash... done.
flashrom -p serprog:dev=/dev/ttyACM0:115200 -r uno.rom

we have:

4.77s user 0.65s system 1% cpu 6:02.43 total

Tested chips

  • SST25VF016B => huge issues, not recognized by the 3.3v version, had to use the 5v version which is over maximum allowed voltage, also had to lower the serial speed to 115200, ultra slow to write(seem related to the chip itself, since that with the openmoko programmer it's even slower...)...
  • W25X80 works well in 3.3v mode(5v works also but it's highly not advised to use 5v)

Advantages and disadvantages

  • The speed isn't that great(about 3 minutes for reading+writing+verifying a 1M chip) Fixed by by Sebastian Parborg.
  • Voltage issues( SPI levels are at 5v, it's problematic for flashing 3.3v chips...)
  • it is made of very commonly available parts(if you can find an arduino uno, you will be able to build it).


  • Find a way to lower the voltage to 3.3v
  • Fix the arduino UNO speed and reliability issues Simply lowering the bauds as advised on the LUFA mailing list long time did fixed it.
  • Write a faster 8u2 firmware
  • Look at other AVR targets
  • Look if it's portable to other architectures (like ARM).