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