Arduino flasher 3.3v

Introduction

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

HOWTO

First download frser-duino:

git clone --recursive https://github.com/urjaman/frser-duino.git

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
# make flash-ftdi

• 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.
• Get an USB cable and don't connect it to the computer
• Connect it to the FTDI adapter
• 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
• Connect the USB cable to the computer.

Flashing

• Run flashrom like that:

flashrom -p serprog:dev=/dev/ttyUSB0:115200

Research and thanks

• At 3.3V setup doesn't work with frser-duino default settings (make ftdi && make flash-ftdi)
• Thanks a lot to SwiftGeek on IRC (#libreboot on Freenode) for finding and explaning to me how to workaround it
• I still need to understand why it works when lowering the clock, it is probably related to the crystal. I need to look in the atmega328P datasheet to understand.