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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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| Caveats:
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| * 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.
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| * For now it requires to patch frser-duino
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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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| === Build the code and flash it ===
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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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| cd frser-duino
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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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| === Build the programmer ===
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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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| {| class="wikitable" border="1"
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| ! Arduino
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| ! USB<->Serial port adapter
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| |-
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| | RX
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| | TX
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| |-
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| | TX
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| | RX
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| |-
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| | 5v
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| | 3.3v
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| |-
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| | GND
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| | GND
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| |-
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| |}
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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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| {| class="wikitable" border="1"
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| ! Arduino pin number
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| ! Function
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| ! Flash chip function
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| ! SOIC8 Flash chip pin
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| ! SOIC16 Flash chip pin
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| |-
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| | D13
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| | CLK
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| !
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| | CLK
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| |-
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| |}
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| * 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.
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| == Flashing ==
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| Run flashrom like that:
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| flashrom -p serprog:dev=/dev/ttyUSB0:2000000
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| With some strange macronix flash chip (that are present in the Thinkpad X200) you might need to add spispeed=100k like that:
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| flashrom -p serprog:dev=/dev/ttyUSB0:2000000,spispeed=100k
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| == Thanks ==
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| 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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