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| == Introduction ==
| | {{#externalredirect: https://www.flashrom.org/supported_hw/supported_prog/serprog/arduino_flasher_3.3v.html }} |
| This explains how to:
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| * Easily lower the voltage of an arduino
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| * Use that arduino to flash a coreboot image on a GM45 Thinkpad with a SOIC16 chip
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| It requires:
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| * An AVR Arduino at 5v
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| * An USB<->Serial adapter capable of providing enough current to power up:
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| ** The arduino
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| ** The flash chip
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| ** The circuits around the flash chip
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| It was tested with:
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| * An Arduino.org "nano version 3.3"
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| * A Sparkfun "FTDI Basic 3v3" (Uses an FTDI FT232R)
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| == Theory ==
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| In the [http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42735-8-bit-AVR-Microcontroller-ATmega328-328P_Datasheet.pdf 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.
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| == HOWTO ==
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| First download frser-duino:
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| git clone --recursive https://github.com/urjaman/frser-duino.git
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| Then modify the F_CPU value in main.h to be 12Mhz instead of 16Mhz:
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| F_CPU will look like that:
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| #define F_CPU 16000000UL
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| Change it to:
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| #define F_CPU 12000000UL
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| * Flash the Arduino with frser-duino
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| # make ftdi
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| # make flash-ftdi
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| * Connect the FTDI adapter to RX and TX of the arduino
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| * Connect the 3V3 of the FTDI adapter to the 5V pin of the Arduino
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| * Connect the GND of the FTDI adapter to the GDN of the arduino.
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| * Get an USB cable and don't connect it to the computer
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| * Connect it to the FTDI adapter
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| * If you use a clip (Like a SOIC-8 or SOIC16 Pomona clip), connect it to the arduino
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| * Connect the chip to the clip, or if you don't use a clip, the chip to the arduino
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| * Connect the USB cable to the computer.
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| == Flashing ==
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| * Run flashrom like that:
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| flashrom -p serprog:dev=/dev/ttyUSB0:115200
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| == Research and thanks ==
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| * At 3.3V setup doesn't work with frser-duino default settings (make ftdi && make flash-ftdi)
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| * Thanks a lot to SwiftGeek on IRC (#libreboot on Freenode) for finding and explaning to me how to workaround it
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| * 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.
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